Continued from Part I

New entries indicated by ***

Of late I have been observing primarily with my 8” f/5.9 reflector.  After collimation, I check the seeing via visual observation at moderately high power on tight and/or magnitude contrast doubles—this is how I happened on this pair of doubles in Draco.

STT 312AB and STF 2054AB appear to the naked eye as the single star Eta Draconis.  Starting in Ursa Minor, a straight-line path from Kochab through Pherkad gets me to Eta as shown in the annotated Cartes du Ciel screenshot below.

 

 

I like to start with the fainter pair, STF 2054AB which is  a mere 12’ due North of Eta Draconis.  In 2017 this mag 6.2/7.1 pair had a separation of 0.943”, which is in line with historical speckle data.  At 345x, I saw two whitish stars of slightly uneven magnitude that were clearly split with dark space between the stars.  I gauged the seeing by estimating how often the image sharpens to two distinct discs.

The 2nd Ed. of CDSA lists STF 2054 as a (2) + 1 triple, meaning the A component is really AaAb.  Stelle Doppie informs the AaAb pair is CHR 138AaAb with a separation of 0.222” (1990)—perhaps those with larger glass can see this as oblong?

Moving on to the brighter object, Eta Draconis or STT 312 AB is where the fun starts.  This mag 2.8/8.2 pair has a separation of 4.68” as measured by Gaia satellite (2015.5)  Using the same eyepiece you used for STF 2054AB, try to find the faint secondary without prior position angle knowledge.  It will be quite small and about 4.5x farther than the distance between the stars comprising STF 2054AB. 

My first attempt at detecting STT 312 B required almost a half hour of moving my eye from averted to direct vision before I definitively saw the tiny speck of light corresponding to the companion.  On a subsequent night, I found the secondary right away because I knew where (and how) to find it.  The more steadily the diminutive B presents as a dot of light, the better my seeing.  Of course, darker skies will also aid your efforts for seeing the faint companion. 

STF 2054AB and STT 312AB help me gauge my local seeing and are fun to look at.  Have you looked at these stars lately?

Nucleophile(Austin, Texas, USA): from an online thread entitled, Fun in Draco: Proximal Pairs STT 312AB and STF 2054AB

Perhaps the aforementioned objects are too easy and you desire a greater challenge; if so, head about 11 degrees due south of Eta Draconis to Hu 149

This pair of ~matched magnitude 7.5 stars has a separation of 0.66″ (last precise in 2017 = 0.665″; my own measure in 2017 = 0.662″)  The pair are slowly widening:  Burnham (1978) lists the separation at 0.5″

Using my 8″ reflector, I observed this object last night and logged the following observations:

345x:  image transforms from elongated to notched (snowman) about 30% of the time; both stars are light orange-yellow

460x:  now seen as sitting on the border of resolved to two discs and split with the tiniest of black space between the discs

Below is an inverted image of Hu 149 I assembled in 2017 using my 15″ reflector and an ASI178MC camera at f/23 operating in mono mode.

 

Nucleophile(Austin Texas, USA), from an online thread entitled; Fun in Draco: Proximal Pairs STT 312AB and STF 2054AB

Attached are some recent pictures of these double stars.  In all cases, N is up and E is left.

I obtained the images using my 15″ reflector and an ASI 290MM cooled CMOS camera.  An imaging train of Paracorr type 1 (setting 5), Powermate 2.5x and a Baader Orange filter gives an f ratio of 13.3  Images were collected using either SharpCap or Firecapture. 

Measures were made with Speckle ToolBox.  Composite images were assembled in Registax.

First up is STF 2054AB

Dear Mark,

Thanks a lot for your interesting and well-documented presentation of a pair of doubles so well suited to gauging seeing  all year round. Last night I made these my first port of call with a 140mm Maksutov (an OMC 140 made by Orion UK, a good instrument). The physics suggest that the separation of 0.943” which you state for STF 2054AB is at the physical limit possible with this aperture, so I was keen to find out how I would fare.

The day had been hot, seeing was mediocre. I know from experience, though, that the air may calm down in certain phases of the evening, so I just hoped I would catch a good moment. At 75x I saw no hint of a companion of Eta Draconis, but STF 2054AB was definitely elongated. At 130x still no sign of Eta’s companion, but the elongation of STF 2054 became even more evident and it was clear at which end the weaker component stood. Encouraged by this, I went up to 210x. Now STF 2054 was a stretched figure-8 that popped apart into separate discs in better moments of seeing. Somehow quite charming!

I had gone in without PA knowledge and estimated this at 330°. Stelledoppie says 351°. So deviation <10%, that’s OK.

After having trained the eye in this manner, I turned my attention to Eta Draconis at 210x. All I could spot was a disc within a wildly dancing diffraction pattern. Although the B component, with its separation of 4.68”, is more than 4.5x further than the distance between STF 2054 A and B, it is evidently much harder to spot. This was an interesting lesson in the effect of Delta-Mag.

I find STF 2054 quite charming and Eta quite challenging, and will certainly be returning to them often. So thanks again, Mark.

CS, Christopher

C.Hay(Germany), from an online thread entitled; Fun in Draco: Proximal Pairs STT 312AB and STF 2054AB

Finally, here is Hu 149

I measured this one 21 times over three nights in order to gauge repeatability of the measuring protocol.  The current measure matches very well what I obtained a few years back.

rugby, on 19 Jun 2019 – 06:11 AM, said:

I just finished observing STF 2054 AB and STT 312 in Draco using an  SW 120 ED and a Meade LX 10. A very bright moon with Jupiter brightened the eastern horizon.  Unfortunately these pairs lie directly above my house and thus suffer from heat rising from the roof.

What I saw was surprising. 2054 was elongated but not separated in the 120 at 200x.  I had not expected anything because it is on the edge of this scope’s capabilities. I did not try the 8 inch.

STT 312 AB was exceedingly difficult. Without prior knowledge of PA I kept seeing flashes of a tint dot south south preceeding the primary. I used the 120 at 200x. The view in the 8 inch was too turbulent for any resolution.

I am notoriousy poor in estimating position angle.

Hi Rugby,

Give ’em a try with your 8″–I think you will like the views!

Nucleophile( Austin Texas, USA), from an online thread entitled; Fun in Draco: Proximal Pairs STT 312AB and STF 2054AB.

Last night was about my 10th try to find that little bugger hanging out in the diffraction ring. I had tried repeatedly and without success with my 120mm ED. I’ve tried before with my 8″ [Newtonian], even on an EQ platform a few nights ago. This time I managed to see it with the 8″ at an ungodly 498x without the EQ, so constant nudging and then allowing it to drift (if the drifting was near rapids) . I would call it my “great white whale”, but it’s more like a tiny white pimple.

You’d expect the 8″ should easily split it, if I could just get improved seeing.

Chesterguy

Chesterguy( Stillwater, Oklahoma, USA), from an online thread entitled: Zeta Herculis…finally!

 

I just made a 7 inch aperture stop today for my 18. Worked great tonight. I’ve made them many times before but it’s been a while. Seeing tonight was so good the better views were at full aperture..

Darren Drake(Chicago, USA), from an online thread entitled Aperture Mask

DavidC, on 19 Jun 2019 – 03:41 AM, said:

I am making an off axis aperture mask for my 10 inch lightbridge, but using a single 4 inch hole. I got the idea from san francisco sidewalk astronomers, but they had it as plans for a solar filter. I’m making it for planets and double stars. I’ve been told by stepping the aperture down to 4 inches, planets won’t be as bright, therefore I can use more power on them. At 1270 mm focal length, I’m hoping for impressive views on planets by using more power. Am I thinking this correctly?

 

Thanx, David

Waste of time IMO. I have a 10” LB with a very good mirror set. I also have excellent 100 and 120 mm ED refractors. If seeing is equal, the 10” reflector slaughters the excellent refractors in planetary detail.

SteveG(Seattle, Washington, USA), from an online thread entitled: Aperture Mask

Vla, on 20 Jun 2019 – 2:55 PM, said:

Smooth edges have more of a cosmetic effect. Rough edges don’t induce aberrations, because they don’t affect wavefront shape, and unless the edge is ridiculously rough, the diffraction effect will be negligible. As an illustration, effect of a 2-inch focuser protruding into the light path of a 200mm diameter mirror. As much as 1 inch into the light path will take only about 1% of the energy out of the central maxima (which, expectedly, becomes somewhat elongated, because the vertical mirror diameter is effectively shorter).

Yes indeed! The effects are diffractive and tiny, not what we optics guys call aberrations. I also like your focuser signature there… Fourier Transform (impulse-response) says it all.

Masks roughly-cut with scissors or a knife are perfectly fine. The one thing to try to avoid is long straight edges. Those will give noticeable spikes. The three straight edges of the focuser there… do a little bit of that.

On the tech/theory side… there are infinitely many wavefronts that will produce the same impulse response. That’s because the sensor (eye or camera) detects only amplitude, but not phase. So you can’t inverse-transform back to the wavefront by processing on the one image of a star… unless you use two or more (ideally many) focus positions’ images. And that is what we call ~phase diversity analysis~ (what was used to assess Hubble’s flaw). And what is implicitly involved in the various casual ~Sar Tests~ that we often talk about here. 

Tom Dey(Springwater, New York, USA), from an online thread entitled: Aperture Mask

Deep13, on 14 Dec 2018 – 06:56 AM, said:

In my mind, the ideal planet telescope is a 10 or 12″ EQ Newt (split ring?) in a permanent location with a clear view of the south and overhead. Add a good binoviewer, pairs of long ZAOs, and an easy way to reach the EP, and I’d be all set. In reality, it would be too expensive and I have no place to set it up permanently. So-o-o-o, I’ve arranged to buy a used 8″ f/8 EQ-mounted Newt. I’ll need to have some servicing done on the mirrors. I’m thinking that within the realm of likely possibility, this may very well be my ideal set-up. Right now it has no fan and a tall R&P focuser, so I may change those things. And I’ll built a cart for the Meade RG mount. I already have a tall adjustable chair and a Denk II with pairs of TV Ploessls.

 

Any thoughts? What’s your ideal planet scope?

 

I had both a very good 8″ Zambuto f-7.5 and a 10″ Waite f-5.8 on an EQ mount, the 8″ I had rotating rings but still a very big pain in the rear to use on an EQ mount. I am considering a slightly different set up 10″ f-5.3 through f-5.5 for a shorter tube and mounted on an EQ-AZ mount, in AZ mode viewing will be far more easier as the EP will be on one side and accessible.  At the focal lengths mentioned as long as you get a premium mirror and build it well you can achieve 50x per inch with sharp image on the planets, and you can use a 1.83″ secondary, CO 18.3%. good luck.

dag55(Hamburg, Illinois, USA), from an online thread entitled; Ideal Planetary Scope

The Orion 4.5 in f/8 dobsonian could be an option. Seems to get good reviews on the optics here on CN. Lightwieght. I believe the focuser is plastic, but, it should be ok with normal weight 1.25in eps.If the moon with a 4 -5 in reflector is the ojective, this little scope should do a decent job.I have not used the Orion, however, I do have a 4.5in f/8, and I think they are capable little scopes.

Good viewing,

dmgriff, from an online thread entitled, 4-5” reflector recommendation

 

+1 on the AWB OneSky.

I was surprised at how well it works. At 14 pounds total, it might be just what you’re looking for.

Havasman( Dallas, Texas, USA), from an online thread entitled: 4-5” reflector recommendation

The AWB One Sky is fine for the money but its burdened with an very poor helical focuser, preferable is the Lightbridge 130 , discontinued but still available from some dealers, the Zhumell 130, the best of the bunch IMHO or the slightly smaller Zhumell 114 , very similar to the Orion Starblast but less money, the Zhumell is also sold as the Edmund Astroscan Millenium, D.

Binojunky, from an online thread entitled: 4-5” reflector recommendation

 

The Onesky is a fine scope. I have no problem with the focuser.,and the mount is quite stable.,Some of my best spent astro money.,cheers.,

 

Clearwaterdave(Western Maine, USA), from an online thread entitled: 4-5” reflector recommendation

How is a 4″ apo a “no brainer” when the OP specificly asked about a reflector? The OP has other scopes and seems to have some idea of what he’s lookin for.,What scope you think would do a better job for doubles or planets is not what he asked about. If you have used and liked a 4-5″ reflector of any type and you want to share your experience here that would be helpful to the OP.,

Clearwaterdave(Western Maine, USA), from an online thread entitled: 4-5” reflector recommendation

I have had the OS up next to a 102ed and “to my eyes” the views are too similar for me to say either one was “better”.,And there are many many very happy OS owners.,So yes.,you can expect a quality reflector for $200.,That’s the no brainer.,and the OS isn’t the only one.,there are a few good quality 5″ reflectors out there for $200.,YOMV.,

Clearwaterdave(Western Maine, USA), from an online thread entitled: 4-5” reflector recommendation

Thank you again for all the great responses. I’m always pleasantly surprised at the information you guys have and your experience. Yes, optics are my primary concern for the scope, but I haven’t really read one bad review concerning them so I think the OneSky is what I’ll go with. I have a pretty large back deck with a decent view to the south so it will be easy to track the moon every night, even if only for a few minutes. Concerning refractors: the truth is I have little experience with them (I know they’re not hard to figure out) and my comfort level, if you will, is with Dobsonian type reflectors. I have a neighbor down the road who has a 4” Takahashi (I think), and the views through it are really something else. Then he told me the price tag and my mind went to how how big of a Renegade or Teeter I could get for the same price. Plus someone told me that owning a refractor will lead you down to the perilous and very expensive road of astrophotography.
The reason I don’t put the 8” out on the back deck is that I use it specifically for planetary viewing now. I have it in the garage ready to load up for a quick drive into the foothills next to the house. The view is better and I get away from all the house and street lights. At f/7 that 8” gives just wonderful views of the planets. I was also able to complete the AL double star program with. If you haven’t looked at that program, I recommend it as it was one of my favorites to do. The 8” was the first scope I ever owned and I had to rebuild it out of disassembled parts, which I found at a flea market. That was a journey, let me tell me you. But now it’s dialed in with a great mirror and I’ll have it forever.
And with the 10”: that’s my deep-sky, dark site, fall into the heavens scope. I try to get out there at least once, if not twice, a week. It too has great mirror and makes it hard for me to financially justify a larger scope given there’s so much to see with it.
Back to the OneSky. Hopefully it will be what I’m looking for. I have perfect cover and place for it, it won’t get dirty, and when I’m out enjoying the late evening and want a quick peak, it’ll be right there.

Mick Christopher, from an online thread entitled: 4-5” reflector recommendation

One of my all-time favorite 4ish inch scopes is the Orion XT4.5, mentioned by Dave and Ed earlier. It’s a very nicely engineered and accessorized product, and provides sharp high power views with very minimal focus wiggles and immediate dampening times. The long focal length makes the scope forgiving of the somewhat imprecise focuser, which works quite well. It’s also very easy on simple eyepieces, which is handy. It’s not a do-all scope, owing to the focal length and 1.25″ ep limitation, but it’s still capable of providing pleasant low power views, yet shines at moderate and high powers. Add a 5 gallon bucket, inverted, as a “chair” (which can pull double duty as a caddy for charts, ep case, and binos) , and the scope works well for adults without the need to raise the scope on a platform.

KerryR( Midwest Coast, Michigan, USA), from an online thread entitled: 4-5” reflector recommendation

 

If the OP can handle the extra size and cost the Orion XT6″F8 is a fine scope, I picked mine up last years for $300 Canadian brand new shipped to my door, take it out in two pieces, plonk it on the ground and away you go, D.

Binojunky, from an online thread entitled: 4-5” reflector recommendation

 

This report is the third installment of a series of observational investigations I have made using an 8 inch f/5.9 reflecting telescope. 

Check out this link for goals and methods used in this study:

https://www.cloudyni…-and-monoceros/

Corvus
Bu 920 (12158-2321) mags 6.86/8.22; pa = 308°; sep = 1.934”, 2016 (solid data)
345x:  well split with secondary a bit smaller; both stars are yellow; well above resolution limit

B 1716 (12247-2004) mags 9.42/9.42; pa = 230°; sep = 0.701”, 2014 (solid data)
345x:  single star
460x:  a bit elongated, but never resolved despite best efforts; below resolution limit; important data point to set lower limit for fainter stars

Hydra
STF 1273 AB, C (08468+0625) mags 3.49/6.66; pa = 310°; sep = 2.824”, orbital estimate for 2019.3 (solid data)
345x:  easily split to two yellow stars of widely varying magnitude; above resolution limit

Bu 587 AB (08516-0711) mags 5.75/7.41; pa = 121°; sep = 1.186”, 2017 (solid data)
345x:  blur of light that sharpens to a small secondary that is just split
460x:  spit 100% of time; above resolution limit

Bu 219 (10216-2232) mags 6.70/8.52; pa = 186°; sep = 1.773”, 2015.5 (Gaia DR2, solid data)
345x:  split 100% of time; secondary is much smaller and both stars are white; above resolution limit

A 3064 (08403-1518) mags 9.15/9.00; pa = 357°; sep = 0.681”, 2015.5 (Gaia DR2, solid data)
345x:  just resolved to two tiny discs 40% of time; just above resolution limit; important data point to helps set minimum value of rho for faint, equal mag pair

A 338 (08207-0510) mags 8.83/9.39; pa = 17°; sep = 0.569”, 2015.5 (Gaia DR2, solid data)
345x:  slightly pointy
460x:  slightly elongated, but never resolved; well below resolution limit

HJ 4478 (11529-3354) mags 4.67/5.47; pa = 52°; sep = 0.578”, 2015 (data needs confirmation)
627x/orange filter:  elongated that becomes notched 10% of time; just below resolution limit; difficult due to low altitude; requires re-measure to firm up separation value

B 1175 (10582-3540) mags 8.25/9.23; pa = 251°; sep = 0.61”, 1998 (data is old, scant)
345x:  resolved 50% time to two similar magnitude yellow stars; a bit above resolution limit; separation likely greater now; requires newer measures of separation and delta mag

B 218 (12002-2706) mags 9.11/9.69; pa = 340°; sep = 0.472”, 2015.5 (Gaia DR2, scant data)
627x:  very faint; rod shaped at times, but no hint of resolution or notch; well below resolution limit; requires re-measure to firm up separation data

HWE 72 (12136-3348) mags 6.48/8.55; pa = 159°; sep = 1.231“, 2016 (solid data)
345x:  just split 30% of time to two white stars; secondary is much smaller; above resolution limit

Bu 411 (10361-2641) mags 6.68/7.77; pa = 303°; sep = 1.33”, 2017 (solid data)
345x:  just split 100% time to two light yellow stars of somewhat dissimilar magnitude; above resolution limit

Bu 219 (10216-2232) mags 6.70/8.52; pa = 186°; sep = 1.773”, 2015.5 (Gaia DR2, solid data)
345x:  split 100% time; secondary is much smaller and both stars are white; above resolution limit

Leo Minor
STF 1406, aka STT 211 (10056+3105) mags 8.37/9.42; pa = 219°; sep = 0.728”, 2017 (solid data)
345x:  just split from resolved 30% time; stars are faint, white, and seem to be of similar magnitude; above resolution limit; a newer delta mag measure desired

Lynx
STT 159AB (06573+5825) mags 4.45/5.50; pa = 236°; sep = 0.704”, orbital estimate for 2019.3 (solid data)
345x:  single star
460x:  possibly pointy
627x:  at times elongated showing secondary as smaller, but never resolved; below resolution limit; it is unclear why this is so difficult—perhaps there is a ‘brightness’ factor that needs to be incorporated?  Revisit next year using orange filter and get a new measure.

COU 2607 (07441+5026) mags 5.33/8.43; pa = 164°; sep = 0.973”, 2012 (data is a bit old but is considered solid)
460x:  secondary pops into view as just split 50% of time; just above resolution limit

STT 174 (07359+4302) mags 6.62/8.26; pa = 92°; sep 2.170“, 2015.5 (Gaia DR2, solid data)
345x:  split 100% of time; both stars are white and secondary is much smaller; fine mag contrast double; well above resolution limit

Hu 850 (08094+3734) mags 9.42/9.23; pa = 349°; sep = 0.57“, 2016 (scant data)
345x:  viewed for an extended period of time using averted vision shows the pair exhibiting a notch just past extended a mere 10% of the time; never resolved and is considered below the resolution limit; a re-measure of separation is needed

Ursa Major
STT 232AB (11151+3735) mags 8.02/8.90; pa = 243°; sep = 0.623”, 2015.5 (Gaia DR2, solid data)
552x (Pentax 2.5XO/Paracorr Type 1, setting 1):  pointy about 25% of time, but never a hint of being resolved; below resolution limit

STT 235AB (11323+6105) mags 5.69/7.55; pa = 44°; sep = 0.949”, 2019.3 (orbital estimate, solid data)
345x:  on the resolved/split border with secondary seen as much smaller
460x:  cleanly split; primary is yellow, secondary is light orange; above resolution limit

STF 1770 (13377+5043) mags 6.93/8.18; pa = 128°; sep = 1.722“, 2015.5 (Gaia DR2, solid data)
345x:  cleanly split; primary is light yellow while the smaller secondary is light orange—a fine pair; above resolution limit

STT 200 (09249+5134) mags 6.53/8.57; pa = 337°; sep = 1.251”, 2015.5 (Gaia DR2, solid data)
345x:  close split (AV helps to see fainter secondary)
460x:  easily split to two stars of unequal magnitude—very nice; above resolution limit

STT 232AB (11151+3735) mags 8.02/8.90; pa = 243°; sep = 0.623“, 2015.5 (Gaia DR2, solid data)
552x (Pentax 2.5XO/Paracorr Type 1, setting 1):  pointy about 25% of time, but never a hint of resolution; below resolution limit—important data point for calculator development

A 1346 (09591+5316) mags 8.84/9.66; pa = 179°; sep = 0.624“, 2019.3 (orbital estimate; data is incongruent between orbital estimate, historical speckle and Gaia DR2)
345x:  slightly elongated; very difficult
460x:  moves past elongated to notched <10% of time
627x:  possibly seen as resolved 10% of time with averted vision; just below resolution limit; requires re-measure to firm up separation value

STT 229 (10480+4107) mags 7.62/7.92; pa = 254°; sep = 0.63“, 2019 (estimate from 4th Interferometric Catalog; data incongruent between historical speckle, orbital estimate and last precise)
345x:  moves past pointy to resolved 30% of time showing secondary as a bit smaller versus the primary
460x:  persistent snowman shape that sharpens to nearly split 30% of time; just above resolution limit; re-measure of separation needed for this important data point

Bu 1077AB Dubhe (11037+6145) mags 2.02/4.95; pa = 336°; sep = 0.802“, 2019.4 (orbital estimate, solid data)
460x/orange filter:  very difficult; secondary pops into view 30% of time as just split—otherwise, it is merely a blur of light/brightening of first diffraction ring; at or just above resolution limit

**Have you observed or imaged any of these objects recently?  Let me know.  Perhaps you have a suggestion for a double I should observe—I’m all ears!

Nucleophile(Austin, Texas, USA), from an online thread entitled; Investigations With an 8 Inch Reflector. Part I: Canis Major, Canis Minor, Lepus, and Monoceros

My preference is in the “or” category. I have used all of my scopes for doubles, but I love my 10 inch reflector… it is a double star magician… except for Sirius B… just can’t get that one in the 10 inch. But I have split it ONCE with my 4 inch achro (retired this one to give to my granddaughter)… she loves doubles too…

SeaBee1, from an online thread entitled; scope preference for doubles

So much for Newtonians not being suitable for observing high-resolution double stars eh?

Mr. Hardglass

 

Sol, that the primary is 8.38″ in diameter is a revelation. I assumed it was the standard 7.9″. When I stow it away for the monsoon, I need to measure it. That’s kind of cool, but definitely non standard for a Newt, yea? I wonder if they are using 8″ SCT blanks that are (supposed to be) a little bit ‘over sized’. Just curious.

When I do the math for a 2.6mm diagonal support, I get 2.6/8.38 = 31% obstruction. Not a ton of difference, but comforting to some. My MCT has a 30% +/- obstruction and offers no ill feelings. The images are nice. It should have the contrast of a 8.38 – 2.6 = 5.8″ refractor, and you do not hear folks complaining about those views. It still puts ~90% of the maximum light into the Airy disc compared to a perfect 5.8″ APO. It’s right at the diffraction limit with a descent (not premium) mirror.

Abytec(Pampanga, Philippines), form an online thread entitled: ES Firstlight 8inch dob vs. Skywatcher 8inch dob

Actually I took lots of measurements regarding the E.S. 8, and measured many times. Not because I was obsessively compelled to, but I had an opportunity to acquire another 8″ mirror with a “pedigree”. So I needed to know if I would be able to use the E.S with little if any modification for an actual 8″ diameter with a traditional 1.4″ thickness to work.

To the original O.P. the stock E.S. primary is also 7/8″ thick so the 6 point floating cell is just another little plus for the E.S. over the GSO or Synta.

With the stock E.S. 8 that’s well collimated and cooled Jupiter showed a bit better than TEC140 with really good, (8P) seeing. On D.S.O. no contest.

Sol Robbins(astronomical author and distinguished sketcher), from an online thread entitled, ES Firstlight 8inch dob vs. Skywatcher 8inch dob

Hi all,

Please find attached a drawing of Jupiter I made last night with my 8 inch Newtonian in my home observatory.  I have to say, I was quite impressed with image quality- the details on the disk were easier to see despite the low altitude of the planet.  The main feature was the dark and turbulent SEB(s), and the start of the STropB in the South Tropical Zone.  The EZ was rather active as was the NEB, the NTB and NNTB contained darker sections.  Io is shown in the drawing and was probably the strongest colour I have ever seen, no doubt this is due to the low altitude.

Best wishes,

-Paul

 

Paul G. Abel(author, BBC Sky at Night presenter, Leicester, UK), form an online thread entitled: Jupiter and Io last night.

 

 

From practical experience I have found optical quality, coating quality, proper baffling and eyepiece used more important to contrast than CO size once its below around 30%. Why small APO’s out perform slightly larger obstructed scopes is usually NOT due to being un obstructed but optical quality, mechanical quality and other factors. A smaller CO is nice, but can limit your fully illuminated field and eyepiece choice. Theory is great, but assumes everything is equal which it seldom is.

The biggest enemy of contrast is scatter, stray light and optical quality if you have a reasonable size CO.

Richard Whalen(Florida, USA), from an online thread entitled, Secondary Mirror Obstruction?

TOMDEY, on 02 Apr 2019 – 9:46 PM, said:

A six-inch scope with a 30% diameter obstruction resolves far better than an unobstructed five-incher. Just generate the non-normalized point-spreads and MTFs to see that in action!

 

PS: This is why a (good) modest-sized Dobsonian will always blow the socks off a good smaller refractor (any smaller refractor!) for both light-gathering and resolution!

 

But, gota admit… refractors make fine finder scopes on big Newtonian reflectors…    Tom

Every time I see yet another thread about secondary mirror sizing and central obstruction (particularly when the MTF graphs start appearing), I say what Tom said above – just use a slightly larger telescope and don’t worry about it.  (And those little refractors do make very nice finder scopes.)

However, I will also add something else – if you undersize the secondary or size it to only fully illuminate the very center of the field, then you are:

 1) using the part of the secondary that is most likely to have a defect,

 2) using the part of the secondary that might roll off due to cooling,

 3) using the part of the secondary that is often left out of the interferometric analysis, and

 4) forcing yourself into very precise placement of the secondary in order to get something close to a fully and symmetrically illuminated field (in other words, making it very hard on yourself for very little gain).

My method to size secondaries for most telescopes is simple – add 4″ to half the mirror’s diameter to get the intercept distance.  Then divide by f/#.  Then go up one flat size if the calculation yields a size that is close to a standard flat size.

So, if I calculate that a 3.1″ or 3.2″ flat is needed, I go to 3.5″.  At 3.4″ – 3.5″, go up to 4.0″.

The 4″ added to half the mirror’s diameter just allows the use of a filter slide underneath a properly placed SIPS or Paracorr 2.  For a little more breathing room, use 4.5″ in the calculation.

Try this on various commercial Newtonians and you’ll find that some have secondaries that are too small…..

Mike Lockwood(premium large aperture mirror maker), from an online thread entitled, Secondary Mirror Obstruction?

Whew! for my 36-inch F/3.75… that comes out to (18+4)/3.75 = 5.9″ … and mine is 6.25″, with a nice wavefront! And, frankly… even a tad bigger than that might be prudent. I just happened to already have the 6.25 and characterized the wavefront at work… figured a known good one would keep the project hustling along!  I then teased the focuser as close in as possible… reducing that four inches to about three. When I focus my farthest-innie eyepiece… only have a few mm to spare! 

Tom Dey( retired optical scientist, Springwater, New York, USA), from an online thread entitled, Secondary Mirror Obstruction?

 

A number of factors are working against reflectors:

1. Reflectors have central obstructions, which reduce the resolution.There’s also a bit of loss to the spider, which creates diffraction spikes.

2. Reflectors tend to have problems with temperature differentials within the tube, which creates air currents that distort the image.

3. Mirrors have more scatter than lenses.

4. Reflectors have a harder time staying in alignment than refractors.

5. Reflectors have coma. Refractors have their own problems (chromatic aberration and spherical aberration) but expensive glasses and lens designs can basically eliminate these.

6. Refractors are usually higher end than reflectors (so, they tend to be higher quality).

However, you can usually resolve these:

1, 3. Reflectors scale up far better than refractors, so they can have more aperture, which helps compensate for these problems. Obstruction sizes can be minimized, curved spiders will spread the diffraction spikes around and make them less apparent.

2. Intelligent fan usage can do a lot for air current formation. Good telescope design can keep cool-down times reasonable and mostly eliminate this issue in use.

4. It’s pretty easy to get good at reflector collimation. Just keep it collimated.

5. Coma can be mostly eliminated through use of a paracorr. Or, you can use a longer focal ratio.

6. There are premium mirror-makers who produce mirrors up to the quality of the best lenses.

If you resolve these issues, reflectors still do not perform up to the standard of a refractor of the same aperture – but will perform as well as a refractor that is slightly smaller. However, you can get a reflector that is far larger than any refractor you can get. It’s reasonably feasible to get a 12-16″ dobsonian with premium optics and good thermal management, and that will (under good conditions) walk all over any refractor anyone with a normal income will ever be able to afford.

Mitrovarr(Boise, Idaho, USA), from an online thread entitled; Why are refractors considered to be sharper than reflectors if resolution is a function of the aperture?

Refractors typically do not suffer from thermals, are typically in excellent collimation, are baffled better, and don’t have a center obstruction.

The number of reflectors that are miscollimated is astronomical. So overall I think you have a better chance of having a excellent experience with a large APO refractor. BUT, find a 10″ or bigger 1/6th wave or better, perfectly collimated reflector and it will knock your socks off.

Whichwayisnorth(Southern California, USA), from an online thread entitled; Why are refractors considered to be sharper than reflectors if resolution is a function of the aperture?

That Dalek, on 03 Mar 2017 – 01:35 AM, said:

Just a question that came to me. Thanks for any answers!

Refractors often have better definition, which is the ability to show fine, low-contrast detail.  A reflector solves that problem by being larger, gathering more light and having higher resolution.

A old rule of thumb is that a 6-inch Newtonian, properly designed and built, will beat a 4-inch refractor.

Caveman_Astronomer, from an online thread entitled; Why are refractors considered to be sharper than reflectors if resolution is a function of the aperture?

I will simply say that what we perceive as “sharpness” is not resolution.. A few comments, experiences, thoughts.

– If I look at 52 Orionis, a 1 arcsecond double star in my 120 mm Orion Eon. It is very close to the Dawes limit so on a perfect night, the disks are overlapping and its difficult split at best. If I point my 10 inch F/5 Dob at 52 Orionis on that same night, and the scope is cooled and of course collimated, 52 Orionis is split wide open. Much smaller disks widely separated.

In this case, I see 52 Orionis as much sharper in the 10 inch.. But most often, I think the comparisons of both contrast and resolution are made in relative terms, at a 0.5 mm what do I see?

– Looking at the Globular M79 in Lepus is a 6 inch refractor versus my 22 inch Dob, few would perceive that the refractor was sharper.. M79 in the 22 inch looks about like M13 in a 10 inch. M79 in a 6 inch looks, well we know what it looks like..

– Reflectors are fininky to the uniniated.. They require care and attention.. Collimation and thermal management are important..

It always seems there comparisons are made between some sort of ideal refractor and the average faster Newt. An 120 mm F/5 achromats versus a 130 F/5 Newtonian.. I think most would (f)ind the Newtonian sharper…

Jon Isaac(San Diego, California, USA), from an online thread entitled; Why are refractors considered to be sharper than reflectors if resolution is a function of the aperture?

mogur, on 04 Mar 2017 – 02:19 AM, said:

 

dugpatrick, on 03 Mar 2017 – 01:53 AM, said:

All good points.  But, yes, resolution is better with larger aperture.  An 8″ newt will have better resolution than a 4″ APO. And better CA.

 

Doug

Only if it’s PERFECTLY collimated! (a rare find) And I’ll take a little CA over loss of contrast because of a spider vane and secondary obstruction.

 

Perfect collimation of reflectors is not hard to obtain, with the right tools (Glatter laser + TuBlug or Catseye cheshire + autocollimator).   But not every reflector owner is so demanding of collimation, nor willing to spend for the top-level tools that reliably produce perfect collimation.  OTOH, others of us are a bit happily OCD about collimating our reflectors.

FirstSight(Raleigh, North Carolina, USA), from an online thread entitled; Why are refractors considered to be sharper than reflectors if resolution is a function of the aperture?

Apo refractors exist in a sweet spot where their unobstructed aperture and single-pass light path tends to produce better images than similar aperture reflectors in the same seeing conditions. Most amateurs view with seeing conditions that put anything larger than about ten inches at a disadvantage because the scope resolution is limited by the seeing, not the aperture. With steady seeing and constant temperatures (e.g. Florida) reflectors can do just as well as apo refractors for visual use.

GJJim, from an online thread entitled; Why are refractors considered to be sharper than reflectors if resolution is a function of the aperture?

mogur, on 04 Mar 2017 – 02:19 AM, said:

 

dugpatrick, on 03 Mar 2017 – 01:53 AM, said:

All good points.  But, yes, resolution is better with larger aperture.  An 8″ newt will have better resolution than a 4″ APO. And better CA.

Only if it’s PERFECTLY collimated! (a rare find) And I’ll take a little CA over loss of contrast because of a spider vane and secondary obstruction.

 

The difference in inherent resolution between an 8-inch scope and a 4-inch scope is so vast that the Newt would have to have disastrously poor optics or be really badly collimated to flunk this particular test.

Operating at the magnifications useable in a 4-inch APO, the loss of contrast due to the 8-inch Newt’s central obstruction is barely detectable.

Tony Flanders(Former Sky&Telescope Editor, Cambridge, MA, USA), from an online thread entitled; Why are refractors considered to be sharper than reflectors if resolution is a function of the aperture?

osted 04 March 2017 – 08:23 AM

Refractors are great. Too bad they are all so small in aperture

Caveman_Astronomer, from an online thread entitled; Why are refractors considered to be sharper than reflectors if resolution is a function of the aperture?

caveman_astronomer, on 04 Mar 2017 – 1:40 PM, said:

 

Cpk133, on 04 Mar 2017 – 1:25 PM, said:

God, or natural selection, depending on your persuasion, seems to favor refractive optics for wide fields, low maintenance, and the sharpest views per mm of aperture.

What kind of refractor should I buy that would compete with a 12-inch Newtonian?

 

This 10″ refractor should do the trick.  http://www.cloudynig…nch-tec-at-wsp/

 

$50 000 + $15 000 for the mount and $8 000 for the tripod.

 

Cotts(Madoc, Ontario, Canada), from an online thread entitled; Why are refractors considered to be sharper than reflectors if resolution is a function of the aperture?

russell23, on 04 Mar 2017 – 3:24 PM, said:

 

treadmarks, on 04 Mar 2017 – 3:14 PM, said:

People often say refractor images are more “aesthetically pleasing” (sharper?) even if they don’t show more detail. Aside from the quality issues mentioned, I’m thinking it’s also because smaller telescopes are more resistant to bad seeing. My understanding of the theory is that larger telescopes can have better contrast through brute-force, by having more clear aperture. So it’s not the contrast giving refractors more aesthetic images, it’s their smallness and the fact that refractors take the most advantage of that smallness.

That certainly could be part of it.  Another factor for me is the simplicity of the observing.  I am able to sit at the back end of the scope and sight along the tube to locate objects or stars for star hopping.  The viewing is always comfortable like that and sighting along the tube with your eye next to the eyepiece is not as easy with a newt.

 

Like I said – I’m not ant-Newtonian.  I might even look to pick up a large dob when I retire.  But for now I’m very happy with what I have.

I think a Newtonian is actually easier to point.  Imagine an object 75 degrees elevation.  With a refractor,  it is very awkward to position my head to look along the tube or through a red Dot or Telrad finder.  With a Newtonian,  the focuser and finders are at the sky end of the scope,  I just lean over,  glance through the Telrad,  point the scope, comfortable and effective. 

Jon Isaac(San Diego, California, USA) form an online thread entitled, Why are refractors considered to be sharper than reflectors if resolution is a function of the aperture?

Quote

I don’t even use a finderscope with my refractor.    The first thing I did when I bought the 120ED was sell the finderscope.     My widest TFOV eyepiece serves as my finderscope.  Sometimes that is the 40mm Pentax XL (2.8 deg TFOV).  Sometimes that is the 32mm plossl, 32mm Brandon or 28mm Pentax XL (1.6 deg TFOV).  Or if I’m feeling really interested in a challenge I might even use the 12mm XF or 9mm Morpheus (0.77 deg TFOV) and go sweeping for the target.    I sight along the tube to locate stars to starhop from or a lot of times I just point the OTA right to the location of the target.   I find it remarkably efficient.

Like I said,  I can make it work..  You talk about spending more time observing the object,  working a list of double stars at 60 degree elevation with a 50 mm RACI finder is much more efficient than awkwardly sighting along the tube,  and then using a wide field eyepiece to locate the object.. 

With my short focal length refractors,  I generally just shoot from the hip..  But there is no doubt,  the Dob  with the Telrad and RACI finder is much better for easily finding more challenging objects. 

Jon Isaac(San Diego, California, USA) form an online thread entitled, Why are refractors considered to be sharper than reflectors if resolution is a function of the aperture?

 

Richard Whalen, on 04 Mar 2017 – 6:14 PM, said:

Planets, brighter DSO objects or the moon in high contrast the refractor can be the best choice.

…

After more than 50 years observing, I find the aesthetics of the view more important than the brightness. Also part of the experience for me is also sitting out under the stars on a perfect night and seeing the silhouette of that long white tube against the background of a sky full of stars. Somehow it’s how it should be, and all is right in my world.

I know what you mean; there’s something about those grand old 6-inch achromats on their massive German equatorial mounts that sends a chill down the spine. The views are incredibly clean, and the scopes are big enough to yield some very detailed views of the planets — but just barely big enough.

The fact remains that a 12-inch Dob is far cheaper and more portable than a long-focus 6-inch achromat. And while its aesthetics may be lacking, on a good night it can deliver far more planetary detail than said achromat.

Tony Flanders(Cambridge, MA, USA), form an online thread entitled, Why are refractors considered to be sharper than reflectors if resolution is a function of the aperture?

mlbex, on 17 Mar 2017 – 6:34 PM, said:

When is the last time a major observatory built a refractor? As far as I know, the largest refractor still in use is the 36-incher on Mt Hamilton, built in the 1880s (according to Wikipedia)! It’s still a fine telescope, but there’s a reason observatories are building reflectors. Perhaps they scale better. That wouldn’t really be a problem with everyday astronomers.

Yes, reflectors scale vastly better, for several different reasons. To be precise: false color scales linearly with aperture, large lenses are hard to support, and the glass for a lens has to be perfect throughout its thickness rather than just at the surface. And this is indeed an issue for everyday backyard astronomers.

Refractors pretty much rule supreme in apertures smaller than 90 mm. There are some pretty good 76-mm Newtonians on the market, but they’re only marginally cheaper than equivalent reflectors, and they have a number of disadvantages. So they appeal mainly to people who are really hard-up for money. There are also a handful of Mak-Cas scopes in apertures of 60 or 70 mm, but since the main benefit of that design is small physical size, and 60- or 70-mm refractors are already quite small, the tiny Mak-Cas’s aren’t very popular.

Refractors are also quite competitive in apertures from 90 to 125 mm. But toward the top of that range, the disadvantages of the design are beginning to kick in big-time. At 125 mm, either you end up with a short-focus achromat with tons of false color, or a long-focus achromat that’s really unwieldy and hard to mount, or an apochromat that costs a minor fortune.

At 150 mm, refractors are really a stretch. Very few people can afford apochromats in this size, and with achromats you typically end up with both lots of false color and an unwieldy size. There are nonetheless some people who love 150-mm achromats because of their low light scatter, but that’s truly the end of the line. Refractors bigger than 150 mm (6 inches) are rare indeed in the amateur world.

With reflective designs, by contrast, you’re just getting started at 150 mm. That’s considered quite small for a Newtonian, and not quite there for an SCT. Eight-inch Newts are really cheap and effective, especially on Dobsonian mounts, and eight inches is the standard size for SCTs.

In the modern world of amateur astronomy, where deep-sky objects are the most popular targets, even 8 inches isn’t much. That’s barely enough to resolve most globular clusters or see the spiral arms of the biggest and brightest galaxies. So while refractors certainly have their place for viewing wide fields, for viewing the planets in less-than-perfect seeing, and above all for photography, the fact that they scale up poorly definitely limits their popularity among amateur astronomers.

Tony Flanders(Cambridge, MA, USA), form an online thread entitled, Why are refractors considered to be sharper than reflectors if resolution is a function of the aperture?

Newtonians, provide a natural, simple viewing position for the eyepiece at all apertures. Refractors and Cassegrains require tall tripods and star diagonals. We’re not going to make the artificial distinction and comparison between 90mm refractors and 90mm reflectors or between any other refractors and reflectors that happen to have nominally matching apertures.

Caveman_Astronomer, from an online thread entitled; Why are refractors considered to be sharper than reflectors if resolution is a function of the aperture?

Redbetter, on 20 Mar 2017 – 10:30 AM, said:

 

caveman_astronomer, on 18 Mar 2017 – 1:17 PM, said:

 

Newtonians, provide a natural, simple viewing position for the eyepiece at all apertures.

 

An equatorial Newtonian appears to have some rather unnatural eyepiece positions depending on the declination of the target and the position on relative to the meridian.

No, I’d say that if an equatorial-mounted Newt has rotating rings, it’s always easy to find some comfortable viewing position regardless of where the scope is pointing.

However, I don’t really agree that Newts provide the best viewing position regardless of aperture. I do agree that alt-az mounted Newts (including Dobs) have the best ergonomics of all designs up to a focal length of around 1,500 mm, maybe even to 2,000 mm. But beyond that, they start to require increasingly tall ladders, which begin to get genuinely dangerous and/or scary around 3,000 mm. In those focal lengths, I think that Cassegrain designs are quite clearly superior, due to the fact that you’re observing from the bottom of the tube and the fulcrum is closer to the back than the front.

Refractors certainly have the worst ergonomics, at least in focal lengths above 1,000 mm. They really have the worst of all possible worlds: bottom viewing, long tube, fulcrum far from the eyepiece, viewing angle exacerbates variation in head height rather than counteracting it as with a Newtonian.

Tony Flanders(Cambridge, MA, USA), form an online thread entitled, Why are refractors considered to be sharper than reflectors if resolution is a function of the aperture?

I’ve just recently got myself my first refractor (a 120mm f5 achro) after having used an 8″ f6 dob my whole life. I was actually quite surprised to find the ergonomics much worse and I have had to constantly adjust the height of the tripod to find a good position. Despite this, observing close to the horizon for long periods of time seems quite awkward for the neck.

Olle Erikkson(Sweden), form an online thread entitled, Why are refractors considered to be sharper than reflectors if resolution is a function of the aperture?

300x in an 8 inch is a 0.7 mm exit pupil or about 37.5x /inch. Even my 70 year old eyes can view the planets at magnification levels and more, provided the seeing supports it.

I consider 300 x fine for an 8 inch..

Jon Isaac(San Diego, California, USA),from an online thread entitled, 8″ F/5 Newt planetary and coma

 

 

Richard Whalen, on 09 Jul 2019 – 04:34 AM, said:

How much magnification you can use depends on your optical quality, seeing and your eyesight and aperture. With my 8″ scope I am often around 350x to 450x on Jupiter, and 525x on Saturn. Sometimes higher when conditions are perfect.

 

My rule of thumb is 43x the aperture in inches on a very good night with decent optics, higher for very good or excellent optics. Also much depends on which planet you are observing.

Richard, I am usually between 333x and 400x on Jupiter in my 8″, as well, at 0.6mm and 0.5mm exit pupil. I find 333x (~40x per inch) power to be the most productive and my rule of thumb, as well. At 400x, Jupiter is still workable, but it’s beginning to dim a little. I was looking at Oval BA the other night, it was easy at 333x. I could see it at 400x, but not as easily.  And I am fairly sure at 500x it would have been even more difficult. I accidentally pulled out the wrong eyepiece and hit 1200x once (0.16mm exit pupil!). Not much to see up that high. I guess my optics are not that good.

I get that the quality of our optics produce nice sharp and high contrast images at high power, after all it’s the same quality image we see at less magnification where (lack of) aberration is apparent in terms of resolution and contrast. But I am always interested in the mechanism of how high quality optics can afford higher magnifications at vanishingly small exit pupils, say a bit smaller than 0.5mm, without excessive image dimming. At some point we begin to lose visual sensitivity and, thus, lose the image itself as the eye is working at a very small relative aperture (less than about 0.5mm f/60).

Getting closer to 600x on Jupiter, IME, is unworkable (or at least not as productive as a bit less magnification) in any 8″ aperture even in good seeing. I mean, we can still see some detail up that high, I saw some detail at 1200x, too. Just not much detail was perceived by the eye, even though we are viewing the same fine afocal image we observed at 400x and less. At some point, it becomes less about the optics and more about the exit pupil and, I suspect, throughput as well.

For example, Jove is fine on both 6″ Mak and 8″ Newt at 0.6mm exit pupil, (240x and 333x, respectively). But, at 0.5mm exit pupil, the Mak image is unworkable while the Newt image still had some legs. I suspect this has something to do with the throughput of each scope, not so much about their respective quality or difference in aperture. Of course the 8″ image is brighter, thus affording higher magnification than the 6″. They are pretty close to the same level of quality, not premium but pretty good and roughly the same obstruction. Both were thermally stable and well collimated. Seeing varied from above average to very good in both over time.  (I agree with you in another thread when you talked about stray light control and mechanics, too.) 

But, when I hear folks talk about quality optics affording higher magnification, I am always reminded of the small exit pupil involved and how quality might over come the inverse square law and our own personal level of acuity (as a variable). Unless you or they mean magnification higher than say 1mm exit pupil when poor optics start to become visually and visibly soft, while better optics retain their fine imaging properties until the image surface brightness is no longer supported at smaller exit pupils. Sometimes when folks talk about ludicrous magnification in any scope, and especially in premium scopes, I wish they’d elaborate on what they saw up that high. Tight double stars or a bright planetary nebula? 

I just do not understand how quality affords higher magnification to smaller than 0.5mm exit pupils (very small relative apertures) and well above the magnification where poor image quality becomes apparent. 

Asbytec(Pampanga, Philippines), from an online thread entitled, 8″ F/5 Newt planetary and coma

After 500x the image starts to get too dim in a 8″. This is where a 14.5″ shows it’s stuff at 1000x on Jupiter.

Chas, I know you have great seeing. My seeing is pretty much the same during our dry season monsoon. So, yea, we’re operating at higher magnifications, generally, and on Jupiter, specifically, as well as other objects. I guess that is the crux of my question. Assuming descent optics in both, the 14.5′ at 1000x is about the same as an 8″ near 550x. In my experience with an 8″, the image is less productive starting about 400x and above. Others may vary somewhat, of course.

Unless the optics are truly better in the 14.5″ in appropriately good seeing. Then my question is why can the higher quality, larger 14.5″ aperture show it’s stuff at much higher magnification than roughly the equivelent of an 8″ showing it’s stuff at 400x? The equivelent magnification in the 14.5″ would be about 750x, but why does quality allow it to show it’s stuff at 1000x (equivelent of 550x in the 8″)? I’d love to know what can be seen up that high because, my thoughts are, the 14.5″ image is dimming, too, for the same reason the 8″ is already dimming at 400x and higher.

I’ve seen the Jovian image at 500x and 600x in the 8″, but I would not call it really a great image (on the eye, anyway). There is some detail to be seen, still, and the limb appears to be as sharp. But, a lot of the lower contrast detail is becoming or is already difficult to see. Bright high contrast stuff like double stars are no problem, but Jove is a different animal. It cannot be pushed to ludicrous magnifications, but if it can and optics are the reason, then my question is why and what is seen up that high. A sharp limb, a few belts, the moons, and maybe the GRS?

Asbytec(Pampanga, Philippines), from an online thread entitled, 8″ F/5 Newt planetary and coma

My lifetime-best view of Jupiter in the 12.5″ was at 456x (36.5x/inch), and we could see a knotty white swirl in the salmon colored (then, now it’s more orange) GRS.

The whole disc looked like the surface of an orb, not a flat disc, and the colors were amazing–ochers, pale ivory, bluish tints, grey-greens, reds, whites, blacks, greys, etc.

It was a technicolor image, and super-sharp–sharp enough we could see the shadows of projections on the cloud banks below. And an 18 element stack of lenses in the focuser.

Spectacular seeing conditions, obviously.

On other nights of superb seeing, I’ve gone as high as 986x (79x/inch), just to see if it could be done, but I haven’t been able to see what I saw that night.

The moral of the story is that it is not only optical quality, but seeing that determines how high a magnification we can use.

In absolutely perfect seeing, I’ve used a superb 7″ scope at 160x/inch and the image was OK. I just couldn’t see anything in that scope at 160x/inch

that I couldn’t also see at 100x/inch, though the image of Saturn at 1123x was incredibly large.

But even after all the crazy high powers, give me 400-500x with spectacular seeing, and I can see details on Ganymede and Neptune. 1000x isn’t really necessary.

It’s all about the seeing.

Starman1(Los Angeles, California, USA), from an online thread entitled, 8″ F/5 Newt planetary and coma

 

The short answer is that a good Premium telescope will probably perform noticeably better than an average cheap mass-marketed one. Somewhere between better and way better. But that’s actually a statistical statement. Occasionally a too-good-performing cheap one somehow slips through their QC system… and occasionally a Premium scope will be deficient. The Premium scope is almost always worth the Premium price differential. That is to say — if you don’t want to mess around — just buy the better scope and enjoy it! 

Tom Dey(Springwater, New York, USA), from an online thread entitled: Premium 1/10PV 8″ Newtonian vs mass market 8″ Newtonian.

I owned a Synta 8”f6 Dob along with a custom 8”f6 Dob with a Zambuto mirror for several years. The differences in the views were subtle, requiring side-by-side viewing on rare nights of excellent seeing to confirm. On the other hand, the improvements in the views offered by two inches additional inches of inexpensive aperture were obvious.

If an 8” scope is the largest you want to handle, and you want improved views, premium 8” optics will provide a marginal improvement at about 10x the cost. An inexpensive 10” scope will cost about 2x and the improvements in its views will be obvious. However, premium scopes usually come with premium mechanics in addition to premium optics, and the mechanical improvements are usually obvious under all circumstances.

So, my preferred approach these days is to empirically determine the largest scope that I am comfortable using at an observing site, and then upgrade or replace its optics and mechanics as much as my budget allows

Gwlee, from an online thread entitled: Premium 1/10PV 8″ Newtonian vs mass market 8″ Newtonian.

Make sure that “1/10 wave Peak-to-Valley” rating is on the wavefront, not the mirror surface. Also, make sure the seller has a good reputation.

I went a different route, and had my first Synta 8″ F/6 mirror re-ground by a respected glass-pusher, as its initial figure was quite poor. To fill in the gap while this was in process, I purchased a second Synta 8″ F/6 (yeah, seems like a stupid idea, but the second one was reasonably good). The total cost was lower than buying a complete specialist-built scope, but of course I had to do a little work myself.

I’ve decided to hold onto both scopes for now. I’ve set up the one with the great mirror using a better mirror cell, low-profile focuser, and smaller secondary, optimizing it for high magnifications, while the second scope is for lower mags, with a larger fully-illuminated field.

Like you, an 8″ Newtonian is at my limit for weight and size.

Hoawardcano(Olathe, Kansas, USA), from an online thread entitled: Premium 1/10PV 8″ Newtonian vs mass market 8″ Newtonian.

Starlease, on 19 Jul 2019 – 7:44 PM, said:

Put a Zambuto mirror in my 10″ dob and it outperformed my 14″ claimed 1/8 wave dob for planetary details seen. Little tiny details on Mars seen in 10″ were invisible in 14″.

Your 14″ dob at 1/8 wave is about 1/4 wave at the wavefront – just diffraction limited. It’s possible in extremely good seeing that your 10″ would show more detail, but on an average night I doubt it, unless there are other issues that you haven’t thought about like cooldown, collimation, mounting of optical components, or maybe the claim of diffraction limited of the 14″ isn’t true.

People are always looking for fairy dust they can sprinkle into their telescopes to make them defy the laws of physics. Someone let me know if it works.

Nirvanix(Medicine Hat, Alberta, Canada), from an online thread entitled: Premium 1/10PV 8″ Newtonian vs mass market 8″ Newtonian.

Replacing the 2ndry will probably be the best bet

but you should learn how to star test 

https://youtu.be/QxUQJjjsdW4

Pinbout(Montclair, New Jersey, USA), from an online thread entitled: Premium 1/10PV 8″ Newtonian vs mass market 8″ Newtonian.

Although I didn’t do it with 8″, but with 10″, I think the mirror exchange was a large improvement for visual observations. Views through my GSO 10″ were good, but star tests have shown some astigmatism. Following the advice on this forum, I exchanged the secondary mirror for Antares, but the astigmatism was still there. So, I decided to exchange the primary for the 1/10 pv. The difference is considerable. With GSO mirror, the views were very good, now they are great. I can see many more crispy details on Jupiter, Saturn, Mars or the Moon. Things that were ‘soft’ before are sharper now. And it happens even on the nights with poorer seeing, I just have to wait for the moment in between

For low-power, wide-field DS objects, probably there is no difference, but color: GSO coating produced a greenish touch, OOUK makes it more white/ flat.

With GSO mirror, I often used the aperture mask to see planets sharper. After exchange, in my opinion the aperture mask only makes things dimmer and less sharp, so I guess the scatter light before was bigger with the standard mirror. 

Overall, I have learnt the lesson saying that the exchange for a better mirror was worth it, the telescope is used now more often for the sheer joy of visual hunt for details.

WOJ2007(Tychy, Poland), from an online thread entitled: Premium 1/10PV 8″ Newtonian vs mass market 8″ Newtonian.

After owning a really fine 8” CZ mirror for several years I am always impressed by the views when the mirrors are properly collimated and when the primary mirror has reached thermal equilibrium. Is it better than a mass market 8”? I can’t say because I have no way to compare. It’s also really light for the given aperture (better construction/thinner mirror) without giving up stability.

What I can say about my premium reflector is that the mechanicals beat the pants off my venerable, but flawed 10”. The focuser, balance, bearing smoothness, primary mirror cell, secondary mirror holder are superior in every way. The entire tube is flocked and the cradle design allows the tube to be easily turned and/or moved north south. My definition of a premium scope (which includes the mirror) is one that both offers expected mirror performance while the structure disappears as one uses it. A premium scope is more than a premium mirror and a premium mirror will fall short of full potential if one has to battle with the other parts.

Chesterguy(Stillwater, Oklahoma, USA) from an online thread entitled: Premium 1/10PV 8″ Newtonian vs mass market 8″ Newtonian.

I have two 8ers to compare, one Zambuto 8″ F7, the other a generic “Skywatcher” 8″ F6.

But the comparison is necessarily through memory . . .

I visit family a couple of times per year in Australia. Got tired of lugging my C6 and refractor through airports. So last time back I bought an 8″ F6 “Saxon”, which is the same as the Skywatcher 8″ solid tube.

About a year ago I came across an ad where a guy had the parts for an 8″ F7–the primary being a Zambuto quartz, and the secondary a 1/30 wave Antares. Moonlight single-speed focuser. A solid tube (flocked), and splashed out for an Aurora precision cell. I run it alt-az on a Skytee 2 mount.

How do they compare?

I wasn’t expecting miracles with the Saxon. A solid diffraction limited scope was all I was wanting.

First object was Sirius at high elevation in quite good seeing. Within 2 minutes of setting up the scope on first light I easily split the pup. Done. This is a good scope!

Star test isn’t perfect (I am no expert on this). My recollection was a brighter ring on the outside on one side or the other of focus. So I’m guessing a less than perfect edge. But it performs very well indeed, and more than met my hopes. I haven’t spend much time on planets with this scope (it does perfectly fine). When down under I’m more interested in the Southern objects–Magellanic clouds put up a ton of detail in this scope.

But what about that Zambuto? Well, as far as I can tell it is as close to perfect as you can get in an 8″ mirror. Star test looks identical to my eye on either side of focus.

The mirror is up and ready to go with just a couple minutes of running a fan, and puts up etched views of the planets and moon (it has a very small secondary, and is optimized for planets). A particularly memorable view was of the double double from Mt Pinos (parking lot must be close to 8k ft). Perfect dots and diffraction rings. An observing friend with a lot of experience called it the best view of the double double he’d ever seen.

But how would this thing compare to a 10″. Well, I think you’ll get a more sharp/contrasty view out of the 8″ premium, but so long as the 10″ is decent, it will resolve more detail, those details will just look a tad softer.

Areyoukiddingme, from an online thread entitled: Premium 1/10PV 8″ Newtonian vs mass market 8″ Newtonian.

N3p, on 19 Jul 2019 – 5:57 PM, said:

Has anyone replaced their regular 8″ Synta Newtonian with a higher quality 8″ Newtonian and how was your experience?

The key difference I found was as follows.    During critical observation of an object for 5-10 mins, on the couple of times when the atmospheric seeing snapped into focus- lasting 0.5 to 2 seconds- the mass market mirror would give an “ooh nice” response whereas the premium would give a “wow!” response.

The rest of the time the mirrors were pretty similar.

On galaxies, the higher strehl mirror gave just enough contrast to pass a threshold where the eye could suddenly detect a dust lane.   The mass market mirror couldn’t reach that threshold.

Max T, from an online thread entitled, Premium 1/10PV 8″ Newtonian vs mass market 8″ Newtonian.

 

An inspiring 6″ f/8 ATM build by Matthew Paul, Orange County, New York, USA

Though I did not  build the scope for imaging, I wanted to share what it is capable of under not so ideal conditions. Very happy with the results of the optics. I need to build a better OTA for it. It’s rather flimsy, the spider is not rigid, the tube flexes, and the focuser is just a plastic rack and pinion, but it works very well for now, and the hard part (the optics) are done. Thank you again to everyone that offered information and assistance as I worked on the mirror.

Matthew Paul(Orange County, New York, USA) quoted here

Matthew Paul, on 22 Jul 2019 – 3:32 PM, said:

Though I did not  build the scope for imaging, I wanted to share what it is capable of under not so ideal conditions. Very happy with the results of the optics. I need to build a better OTA for it. It’s rather flimsy, the spider is not rigid, the tube flexes, and the focuser is just a plastic rack and pinion, but it works very well for now, and the hard part (the optics) are done. Thank you again to everyone that offered information and assistance as I worked on the mirror.

MVI_0140-3.jpg

That image ought to give apo owners pause.

Ed Turco(Lincoln, Rhode Island, USA), from the same thread

There is real poetic justice in how well a good Newtonian telescope performs.

JamesMStephens(Hattiesburg, Mississippi, USA), from the same thread.

 

Hello Marty, I can’t answer all your questions, but I did a shoot out between a 150mm f/8 achor and 200mm f/6 dob on Mars a few years ago at opposition.

The Dob was much better, I suspect it had more to do with no CA vs the increase in aperture. Mars was smeared with false color rendering very little detail in the views. I sold the Achro because it was too much for me to mount. And in my light polluted sky, I don’t do much low power deep sky.

I suspect that It would also lose fine detail on Jupiter, but I could not do a side by side compare.

I have a 6 inch 150 f/5 newt, and it does a good job on Juipter/Saturn. I have not had a shoot out between it and say a 100mm ED, or 120 8.3 acrho for a comparison. As far as personal tastes, my eyes are getting old and are light starved, so usually a brighter less crisp image is preferred over a dimmer crisper one.

I suspect …. the best scope for viewing the planets at 150mm without going crazy expensive would be the 150 f/8 dob. I’m looking for one right now in the used market. A 120 ed I suspect would do a good job too, but at 4x the price, and a big mount to boot.

I have an f/5 250 reflector on a dob mount. Best view of Jupiter I have. It does take an hour to cool.

Vtornado( Northern Illinois, USA), from an online thread entitled: 150mm Instrument for Planets, Which Type?

I’ve tried them all over the past 40 years.  Best view of planets was through Newts with good mirrors that were properly collimated. Note the underline, because that (particularly the latter) can be an issue with Newts. For something more compact and lightweight a good 6″ Mak is an excellent planetary scope and it won’t cost you an arm and leg.  I just picked up a used Orion 150 Mak and the (visual) images of Jupiter and Saturn are superb. My old 127 Mak is also good but the 150 gives more edge on brightness.

fcathell(Tucson, Arizona, USA), from an online thread entitled: 150mm Instrument for Planets, Which Type?

I think a 6” f/8 dob, with top notch optics

(Spooner) would be a great choice and affordable.

NHRob, from an online thread entitled: 150mm Instrument for Planets, Which Type?

6″ mak

6″ f/8 newt

4″ fpl-53 double Vixen or triple

will all give great planet views.

tomjones, from an online thread entitled: 150mm Instrument for Planets, Which Type?

tomjones, on 23 Aug 2019 – 01:02 AM, said:

6″ mak

6″ f/8 newt

4″ fpl-53 double Vixen or triple

will all give great planet views.

Why add a 4″ into this discussion when it’s an inferior option?  A good 6″ f8 outdoes it.

azure1961p, from an online thread entitled: 150mm Instrument for Planets, Which Type?

MalVeauX, on 23 Aug 2019 – 6:33 PM, said:

So… to add more to this mix…

 

What would any experienced observers rate a 200mm F6 Quartz reflector to a 150mm F8 ED doublet for planetary views?

 

Would the extra aperture make enough of a difference?
Or would the 150mm F8 ED refractor still throw up the better, higher contrast image?

 

Very best,

The extra aperture would make enough of a difference if the mirror were superb, the tube material, thermal issues, focuser etc., were all finely tuned and working together. Then there are the ergonomics of viewing position and the question of what type of mount will be used.

If one were to buy a used 8″ f/6 “classic” EQ mounted Newtonian from a good source, such as someone here on CN, then that would be a very efficient bang for the buck. Especially if the mirror were a known and proven winner. Probably in the Approximately $500 range vs. $2000 for the 150mm f/8 ED.

“Would the 150mm F8 ED refractor still throw up the better, higher contrast image?” Yes it could, if the 8″ f/6 newt had degraded mirror coating and dust, not collimated perfectly, focuser not smooth, set up on warm surface so that thermals enter the tube and plague the system etc., But in my opinion the Newtonian will win if the details are all taken care of and watched. 

I wish I could find a local old classic 8″ F/6 EQ mounted Newt to play around with, actually…

Everlasting Sky( Vancouver, Canada), from an online thread entitled: 150mm Instrument for Planets, Which Type?

I concur with fcathell, as far as planetary observing with Newtonians when all the necessary conditions are in play. My very best planetary views have been through large truss-tube Dobsonians with premium mirrors, along with large classical Cassegrains, when the seeing has been excellent.

I also agree with Richard Whalen’s post when the aperture is limited to 6 inches.

Dave Mitsky(PA, USA), from an online thread entitled: 150mm Instrument for Planets, Which Type?

Quote

Even with spot on collimation (Newts, DOBs, Maks, SCT’s, etc.) – you still have a central obstruction vs. none in a refractor and that reduces contrast and resolution…even if just slightly — it does

It’s worth keeping in mind that the CO does have a small effect on contrast, not on resolution..

This does mean that a scope without an obstruction, when compared to an other equivalent scope of equal aperture will have reduced fine scale contrast.

But that’s only if the apertures are identical and the optical quality similar. Otherwise, the contrast is affected by the aperture far more than by a central obstruction. This is why large scopes with COs can provide much greater contrast than a scope without a CO.

Some years ago I experimented with my 120 Eon by adding a 40% CO, I could see a loss of contrast but it was surprisingly small.

In this comparison, unless one went with a high quality Newtonians (Spooner) then a $2500 ED Doublet would likely provide better planetary views.

On the other hand, if weight and length were the guidelines, the a good 8 inch Newt would be hard to beat.

Jon Isaac( San Diego, California, USA), from an online thread entitled: 150mm Instrument for Planets, Which Type?

M11Mike, on 24 Aug 2019 – 01:12 AM, said:

Jon – normally I’m with you 99.9%.  But I have seen numerous times FIRST HAND where a quality 4″ refractor beat out much larger apertures on the planets.  And I don’t think the guys with these scopes didn’t have them properly collimated, etc.  These guys with scopes (like the Meade 10″ SCT) were my observing buddies and they concurred.   They were active seasoned observers like myself.

 

Mike

 

Well.. maybe. But you can’t blame that on the CO.  Thermal issues, optical issues, poor seeing..

Try adding a 35% CO to a 4 inch Refractor and see how much difference it makes.

Jon Isaac( San Diego, California, USA), from an online thread entitled: 150mm Instrument for Planets, Which Type?

I’ve had a 6″ F8 newt with 1/8 wave optics and it was excellent for L&P. I’ve got a IM715D mak and the same can be said of it. Big advantage to the mak is in 8 years I’ve never had to collimate it. Either scope would work on my Twilight 2 without a counterweight, I doubt the same could be said of a 6″ refractor. I’ve got an excellent WO ZS110 triplet and it doesn’t outperform my mak or C9.25XLT for L&P unless seeings sub par.

dscarpa(San Diego, California, USA), from an online thread entitled: 150mm Instrument for Planets, Which Type?

First Light Report
Finally, the time had come for first light.  When I put the Glatter laser collimator into the focuser and turned it on to begin aligning the optics, I was stunned to see that the laser beam was hitting the primary mirror inside the circle in the middle of the hotspot.  Despite being driven over 1000 miles and loaded/unloaded twice, the tolerances are tight enough on the telescope. I’ve setup the telescope four different times since – and the initial laser position on the mirror has been inside the 1/4″ (6 mm) hole at the center of the HotSpot every time.  Collimation required less than 1/16 of revolution of any of the knobs on either the secondary or primary mirrors.  I pointed the telescope at the horizon and the zenith.  I moved quickly in altitude and azimuth, and slid the EQ platform through it’s entire range of motion twice.  Collimation didn’t shift.  At all.  
 
Once the sun dove behind the hills just to the west of the observing site, I uncovered the optics and started the fan in earnest to get the optics cooled to ambient as quickly as possible.  I carry a 10″ rechargeable fan that I used to push air at the front side of the primary mirror, and allowed the built in fan to pull air across the back.  The mirror box is only about 8″ deep in total, so air is able to flow easily around the optics and through the structure to help with temperature changes and cooling. Once full darkness had descended up on the observing site, I removed the front fan, rechecked collimation and got to the business of deep sky observing with the new telescope.  I left the rear fan running at full speed, where it’s just audible as a background noise.  Later I turned this down some just to quiet the fan in the silent nighttime desert. Temperatures dropped 23º F (12º C) over the next 2 hours. The thin optics and open structure of the observing rig did a wonderful job of keeping up with the change.  
 
When I first began talking with Mike Lockwood about commissioning a fast, thin mirror he told me that I’d likely never seen what a cooled telescope could really do being that my main observing machine has been a 15″ full thickness OMI mirror in a wooden Obsession structure.  I love that telescope, but I learned on this weekend what Mike was talking about.  Conditions that had been blamed for years on poor seeing were not present on this night, even though we all agreed that the seeing wasn’t any better or worse than a typical night at this location.  I spent nearly all of my time over the next few nights observing comfortably with much higher magnifications than I’d ever been able to use previously. 
 
NGC 5139 – Even though it culminates at just 11º above our southern horizon, Omega Centauri was on the meridian at the end of astronomical twilight, so the three of us agreed that it was the obvious choice for the first target.  We’re all familiar with the views of this object from this site with instruments of all sizes from a 63mm Zeiss refractor to a 20″ f/5 Obsession.  At this low elevation there were some obvious atmospheric artifacts being induced in the image – but we all agreed that this was the finest view we’d had of this granddaddy of globulars.  With a 21mm Ethos I immediately noticed a couple of things.  1 – The telescope maintained perfect balance though it was pointed 10º above the horizon.  When I removed the eyepiece to switch to a lighter one, the telescope didn’t budge.  I’m no designer, but I attribute this to the use of the 30″ altitude bearings and perfectly balanced design.  2 – I was looking at Omega Centauri with 20″ of aperture and a 1.2º true field of view.  The cluster was lost in the middle of a field with all kinds of black space around it. With all that aperture focusing all that globular into the smaller image scale of this wide field, the cluster was astonishingly bright, even by it’s elevated standards.  I hadn’t changed eyepieces or objects yet, and I already knew…..this was going to be a fun telescope.  At 175x in a 10mm Ethos, the cluster is huge, extending nearly to the edges of the field.  What I noticed most was the stars being impossibly tight pinpoints, with black space around them.  The contrast between the globular’s stars and the background sky is the most notable thing from the observation.  
 
NGC 5128 – This beauty in Centaurus is so close by that you can’t *not* look at it.  Again, the contrast was the most noticeable thing about the observation.  With the 10mm Ethos, the dust lane is sharp and well defined across the face of the galaxy and appears nearly bi-sected with a brighter middle – like looking at the great rift from millions of light years away.  
 
I wiled away a few hours working through the Virgo cluster high in the west, spent some time counting galaxies in the Coma cluster and then happened upon what has been the most memorable view through this telescope yet.  
 
M83 – Again, it was the contrast.  An absolute pinpoint of a nucleus with two sharply defined bars extending away for a few arc minutes and then turning sharply to form those beautiful, elegant spiral arms.  What struck me most though was the dark lanes between the arms.  As I continued observing, differences in darkness began to appear in the dark lanes, as well as brighter spots in the spiral arms (HII, OB assocations?).  I didn’t concern myself too much, I just enjoyed the view.  This telescope rocketed this galaxy to a high place on my favorite objects list.  
 
M57 – I put the telescope on this old standby and basically went camping at the eyepiece.  With an 8mm Ethos, the central star was just there.  It didn’t jump out at you….but it was there and required no effort beyond basic averted vision to see it clearly.  I noted galaxy IC 1296 nearby and that it too was pretty easily seen.  This was where I pushed the magnification.  With a 3.7mm Ethos, the telescope is operating at 475x magnification.  In moments where the seeing settled and the air was steady, the optics weren’t even breaking a sweat.  I was able to observe 4 stars seemingly involved with the nebulosity and the central star was a direct vision object at this magnification.  The interior surfaces of the nebula were clearly mottled and uneven and the entire nebula appeard electric green in the eyepiece.  
 
Veil Nebula – Always a favorite, our small group spent a solid hour cruising the wisps of this supernova remnant with the telescope.  With an 8mm Ethos and an O-III filter, the nebulosity glows as if backlit by some artificial LED source in the eyepiece.  I traced the entire outline of the nebula noting how the brighter wisps faded into thinner and fainter ones as I followed until they just seemed to disappear.  There’s a patchwork background of nebulosity that I hadn’t noticed before with my 15″ scope.  

Great friend and fellow observer Alan Strauss told me I needed to remain still while observing M101.  Uhhhhh….okay!  That won’t be hard.  I could sit here all night.  
 
…and then came the planets.  I have listened to Mike Lockwood bang the drum about planetary observing with big aperture mirrors for quite awhile now.  Like I told him afterward, consider me one of the converted.  Jupiter at any magnification was an absolute razor blade of sharpness.  Where I was used to seeing equatorial bands, I was now greeted with a swirling mess of sharply defined festoons and bands within bands.  Viewing Jupiter this night was the best views I’ve had that I can ever remember.  My friend Alan commented a few weeks later that the thing that stood out most to him was how sharp the planetary views were through this 20″ scope – he wasn’t expecting it to perform the way that it did.  I concur.  
 
Just a couple of weeks ago, I set the telescope up again in my light polluted Phoenix backyard to give a quick view of the moon and Jupiter to my lady.  I’ve not been much of a lunar observer since I was a kid, but she is in love with the moon….so, it was time to show her the moon through the new telescope.  She’s not an astronomer by any means….and she’ll be the first to tell you that she doesn’t have those aspirations.  I was stupefied when I looked in the eyepiece.  Stop me if you’ve heard this before – the contrast is unbelievable  – and not just the inky blackness of the crater shadows and brightness of sunlit portions of the lunar surface.  The subtle variations in illumination in the mare and even light differences in color were obvious and a pleasure to behold.  What was supposed to be a quick 20 minute show of the moon and Jupiter turned in to a 2.5 hour session together.  We spent the longest time comparing notes and pointing out features and seeing the smallest details.  The experience has converted me into someone who’s ready to look at the moon again.  I look forward to the intersection of my travel schedule with a break in the Arizona monsoon and a favorable location of the moon so I can repeat the experience.  
 
Conclusion
I wanted big aperture with no ladder and absolutely no compromises on the optical and structural quality of the telescope.  It came with an uncompromising price tag too – but I couldn’t be happier with the combination of the Lockwood optics and Osypowski structure & platform.  Mike Lockwood’s reputation for ridiculously fast, sharp optics is well deserved and I’d even dare say still underappreciated.  I selected Mike as my optician for a couple of reasons.  1 – He was great to talk too and has been a great resource for all astronomy/telescope related questions since first talking with him back in December 2017.  2 – A couple of extremely experienced observers that I respect greatly both said the same thing – that the best view that they’d ever had through a telescope had Lockwood optics.  I can now say I wholeheartedly agree with their assessment. 
 
The Spica Eyes structure built by Tom Osypowski is as nearly perfect as I think it’s possible to build at this point.  It is substantial, stiff and rigid.  It feels like it’s been built for the apocalypse when you put your hands on it.  I chose Tom because of my experience with his EQ platforms and the knowledge that he’s built several telescopes that were both larger *and* faster than this project – so I was confident i would get a telescope that matched my excitement for the EQ platform.  I haven’t been disappointed.  Twice now I’ve done business with Tom.  Both transactions rank as the smoothest, most pleasant money I’ve spent in this pursuit in my lifetime.  I’m proud to be able to say I own one of his telescopes.  
 
Is the telescope truly perfect?  No.  I have two minor quibbles.

• There is some stiction in the azimuth axis.  It’s not paralyzing, but it is there.  I got after it when I got back home with some car wax and a buffing cloth which has improved it.  Part of this issue is comparing it to the buttery smooth goodness that is the motion of an Obsession.  I’ve been spoiled by 18 years of use with my 15″ Classic.  
• The light shroud fits really, really tight.  Getting it pulled down over the structure is a bit of a process.  By process, I mean it takes a couple of minutes.  Once it’s in place – it stays in place and does a wonderful job of blocking stray light but still allowing airflow through it.  So I’ll count my blessings that these are my issues with the telescope.

I realize it’s been long winded, but there’s little information out there about Spica Eyes scopes.  In fact, there’s really not much beyond a different CN thread that was posted a few years ago about a 24″ scope Tom built.  I submit this review and future experiences and observing reports as part of that body of knowledge.  Tom Osypowski tends to fly under the radar when discussing premium telescope builders, but his handiwork is among the absolute best out there.  He and Mike Lockwood have earned every bit of credit that they get for their skills and contributions to our hobby. 
 
Mike

A great shot of the observing site in Portal, Arizona, the 20″ f/3 telescope described here, and the truck/camper that gives me shelter whilst far from civilization for long periods of time.  The light domes are greatly exaggerated in this long exposure.  The one just to the left of the truck is from Lordsburg, NM – 40 miles (64 km) away.  The light dome to the right is from El Paso, TX – 160 miles (255 km) away.

Mike Wiles( Phoenix, Arizona, USA), from an online thread entitled, First Light Report: 20″ f/3 Spica Eyes/Lockwood Dobsonian

 

Recently picked up a used (mint condition) Skywatcher 130mm f/5 PDS reflector OTA (Thanks Tyson). This scope is presently discontinued.

Cosmetics: beautiful black with silver speckles. 9/10

Inclusions: 8/10 (based on the nice focuser)

excellent dual rate 2” Crayford focuser with 1.25” adapter

Vixen style finder mounting shoe

thin 4 vein spider/ adjustable 2° mirror holder

oversized 2° mirror (this scope is designed for photography)

Enhanced 95% coatings on 1° and 2° mirrors

6×30 straight through finder (mine was upgraded to an Orion 8×40 straight through version)

2” 28mm LET eyepiece (not included in my used purchase)

Nice dual hinged mounting rings and Vixen style mounting 7” bar

Peeves:

Crayford focuser is non-compression ring

Crayford focuser has a thread 2” adapter ring using a single metal set screw

(I removed the ring and drilled/tapped 3 holes a 120° and replaced the metal set screw with 3 nylon ones). I actually prefer this type with nylon screws to a compression ring version.

the 2”-1.25” eyepiece adapter is also thread-on. You need to unthread the 2” eyepiece adapter ring and the thread the 2”-1.25” one on. Stupid design, just include a regular 2”-1.25” – compression ring or set screw.

You need a 2” extension tube to reach focus with either 2” or 1.25”, It is not included.

The included 28mm 2” LET eyepiece is junk (I have tried one). Just include a 1.25” cheapo 25mm Plossl eyepiece.

I hate straight through finder scopes, replaced mine with an Orion 6×30 RACI version (very light weight but a larger 50mm RACI maybe a better option.

Optics: 10/10

easily collimation (it arrived in perfect collimation), 1° mirror is center spotted

3 spring loaded adjustment knobs with setscrew locks

95% enhanced 1°/2° mirrors – brighter view than my larger 140mm f/3.64 Comet Catcher

optical testing – easily 1/8 wave or better

Observing: I am mainly a Deepsky observer – this a definite RFT

Fantastic scope, easily punches above a 5” reflector.

easily takes 160X + (TV 4mm DeLite) , 40x/in- you run out of light grasp

From low power wide field (3° +) to high power, does it all.

with high quality eyepieces, I did not need an OCS (Paracorr)

Some Deep Sky highlights: NELM 5.7 Transparency/Seeing Both 3/5 :

the Double Cluster – superb, one of my best views ever (mono view)

NGC 7789 in Cassiopeia (Caroline’s Haystack) – very easy (large smudge with a sprinkling of brighter stars)

M31 group – all 3 members are easy with direct vision – M31 over 2.25°, M110 diffuse oval

M33 – large 3/4° smudge

M81/82 – beautiful contrast in galaxy types

M51 – Both parts easily visible

M13 – easily resolved – perfect image (pin **** stars) at 160x

M27 – amazing with and without filters

NGC 7000 – fantastic North American shape with NPB filter

Veil Complex – see my posting in Observing section (Veil in small scopes)

Future Upgrades:

I have added a 8” dew-shield

I will flock the OTA (either the entire tube or opposite the focuser)

Summary:

An excellent low priced RFT. Amazing Optics.

The few minor “peeves” are easily corrected.

Highly Recommended !!

vkhastro1(Ontario, Canada), from an online thread entitled, Skywatcher 130f/5PDS-mini review

Congrats on your new scope! 

My experience mirrors yours. It is kind of an “unknown” scope, but for my own application it is working better than the Comet Catcher in spite of being smaller and “slower.”

This scope is kind on the stealth list because when I say I have a 130mm f/5, everyone thinks it is a typical 130mm with small illuminated field and 1.25″ focuser and most do not seem to be aware of the 130 PDS.

vkhastro1, on 30 Aug 2019 – 5:19 PM, said:

 

95% enhanced 1°/2° mirrors – brighter view than my larger 140mm f/3.64 Comet Catcher

optical testing – easily 1/8 wave or better

 

These are factors that I used in my decision to move from the Comet Catcher to the 130 PDS.  Now my situation was that I am using image intensified eyepieces and I came to feel that the Comet Catcher was punching well below the f/3.6 spec.

Some of this I thought was maybe due to the need to re-coat the mirrors, but after a painful testing sequence, I determined that the mirrors were OK, but that they were just not transmitting a lot at longer wavelengths (which is important for NV use) and this combined with the losses of the secondary shading and the corrector (which is where perhaps 10% of the loss in near infra red is coming from) meant that the scope simply was not as bright as I thought is should be. I actually think that the entire system transmission (including secondary shading) of the Comet Catcher really does cause it to loose a lot of brightness. I came to feel that the CC was simply much dimmer than it should be for a 140mm f/3.6 scope.

The other issue I had with the Comet Catcher was the sled focuser and the awkward nature of trying to get it to work with a filter wheel.  The 130 PDS though, with its 2″ focuser with plenty of travel made it easy to use a filter wheel.

One important point though is that while it is an “Imaging” scope, I don’t think it will fully illuminate an APS-C size sensor.  My NV monocular has an 18mm image circle, and I can see that there is a little illumination falloff at the edge.  Not bad, but it does not appear to have a fully illuminated circle bigger than maybe 12mm. Probably good for an APS-C with some cropping maybe or a 4/3.

Anyway, as much as I loved the light weight and simplicity of the Comet Catcher, I came to feel that it was much dimmer than the numbers suggested and moved to the 130 PDS and like you, I really feel that it is brighter than the Comet Catcher was. 

Nice scope.   Not many around as far as I can tell though.  

(Also, the image scale was a plus.  An added bonus was that I had enough focuser travel to use the Barlow lens mounted in one of my filter wheel positions.  This Barlow gives me the ability to bump up the power by about 1.5x just by turning the filter wheel and refocusing.  That is a nice benefit.)

Good review of what appears to be a relatively unknowns scope.  Hope you are enjoying it!

Eddgie, from an online thread entitled, Skywatcher 130f/5PDS-mini review

Very informative comments. I picked up one of these a few weeks ago and use it on a Skywatcher Star Discovery Go To mount that I already had. Quick to set up and cool down, great optics and works really well with my Vixen LVW eyepieces. Nothing to dislike at all.

brisdob(Brisbane, Australia), from an online thread entitled, Skywatcher 130f/5PDS-mini review

We are looking into this model and it’s larger models currently.

Skyward Eyes( Skywatcher USA Vendor), from an online thread entitled, Skywatcher 130f/5PDS-mini review

For a number of years I had a SpaceProbe 130 ST fitted with a 2 inch Focuser. I normally used it with a Paracorr.. A Paracorr would address the need for an extension tube.

I have said this before.. a good 130 mm F/5 Newtonian is the closest thing an affordable 4 inch apo Refractor that exists… The 130ST was quite good on planets and doubles as long as it had an hour or so to cool.

I remember one dark night.. I swapped out my TeleVue NP-101 for the 130 mm F/5  with the Paracorr and 31 mm Nagler..it was scary how good it was.. 

Jon Isaac(San Diego, California, USA), from an online thread entitled, Skywatcher 130f/5PDS-mini review

Ya don’t say; I got me one of them there ‘scopes….ken. I’ve no’ got the 2″ focuser mind, but I dinnae really need it. My bestest grab ‘n’ go ‘scope ever. Eye.

Mr. Hardglass

I’m a massive fan of 130 f5’s, even on the ota’s that are limited to 1.25″ ep’s. Very easy to mount scopes, and, when they have decent optics, great all around performers.

Kerry R.( Mid-west Coast, Michigan, USA), from an online thread entitled, Skywatcher 130f/5PDS-mini review

I have been using this telescope for around 6 months now on my evolution mount as an eaa platform. For the cost, it makes an excellent alternative to my 925 for wider field views and it can reach zenith with no problems.

Barkingsteve, from an online thread entitled, Skywatcher 130f/5PDS-mini review

FINALLY a Dob I really enjoy.

Been through many different sizes, ranging up to 16 inches.  For me, a 12.5″ Dob is in the goldilocks zone.  Big enough to astound me with the views, but small enough to use every clear night.

I can’t get enough.  In just 11 weeks of ownership, I’ve used it 42 times, including several trips to dark skies (3.5 hours each way).

Ryan built a masterpiece.  It’s wonderfully engineered & built.  The telescope is so easy to assemble & disassemble. 

In use, it is sheer joy.  The movements are silky smooth, requiring little pressure to track an object even at 300x.

And the views?  Just mind-blowing.  Never thought a reflector could be so sharp and have such stark contrast.  This is the first time I’ve looked through a Zambuto mirror, and the views are as close to a refractor as I’ve ever seen in a mirrored telescope.

During the last new moon, at extremely dark skies, I pulled the old M13/NGC6207 trick on an observer.  I got her to focus on NGC6207 at 250x.  After several minutes, I asked her to nudge the scope downwards slowly.  A gasp soon followed.  Then the hooting & hollering.  I understood her enthusiasm.  M13 looked photographic.

Ryan was very gracious throughout the build process.  He promptly & politely answered all my emails, and was very patient, despite my impatience.  He is a master of his craft, and actually converted me from a refractor guy, to someone who can enjoy the night-sky using both types of telescopes.

Magnitude 7, from a thread entitled, New Moon Telescope 12.5″ Zambuto refract… er… reflector.

 

Aperture. Obviously of a decent quality, but aperture is what reveals detail.

Small telescopes deliver a low magnification sharp looking view, but the fine detail doesnt exist. Its sharp because the magnification is low.

Double the aperture, double the resolution, simple as that, provided the atmosphere obliges! Which it does more often than some people would maintain.

Happy Limpet(Southampton, UK), from an online thread entitled, What’s more important.

If you’re going to use a reflector, mirror quality is very important. I learned this when I had my 2001ish vintage Nova mirror refigured by Mike Lockwood this year. One of the biggest differences I noted was the moon. Before, I could see features on the moon, but the smaller ones could not really be seen, or made sense of, when examined closely. It’s a hard thing to describe, but it was something I noted often, and found frustrating. Detail in the refigured mirror is much clearer in this respect, probably more refractor-like.

If refractors give a more tightly-controlled image than a similar-quality reflector, then that would be the way to go for lunar.

I wonder how much the resolution advantage of a large aperture reflector is lost due to diffraction, coma, viewing through a wider expanse of air and a filter, compared to a more modestly sized apo. Maybe you really need to compare apos to apos.

Mike Tahitub, from an online thread entitled, What’s more important.

posted 09 October 2019 – 08:16 AM

My favorite scope for lunar visual is my 8″ f/9. When seeing is good the view is tack sharp. The best view ever was with my 25″ on a extremely steady night. I was hitting 1000x and still had a sharp image.

Like Jon, no filter.

Keith Rivich(Cypress, Texas), from an online thread entitled, What’s more important.

 

More on Double Stars with a  commercial 8″ f/6 Newtonian

This report is the fifth installment of a series of observational investigations I have made using an 8 inch f/5.9 reflecting telescope.

 

Check out this link for goals and methods used in this study:

https://www.cloudyni…-and-monoceros/

Corona Borealis
COU 610 Theta (15329+3122) mags 4.27/6.29; pa = 199°; sep = 0.85“, (orbital estimate for 2019.3 is a better fit with historical 4th Int. Cat. data vs last precise from 2016)
345x, 460x:  single star
627x:  brightening of diffraction ring that resolves to small dot that is just split 20% of time; at resolution limit and very challenging; re-measure of separation desired

Draco
HU 149 (15246+5413) mags 7.48/7.62; pa = 270°; sep = 0.665“, (2016, last precise; solid data)
345x:  moves past elongated to notched (snowman) 30% of time
460x:  at resolved/split border as seeing allows; both stars are light yellow-orange
627x:  resolution aided with orange filter under excellent seeing conditions; a bit above resolution limit

Image below is from 2017.444

STF 2054AB (16238+6142) mags 6.15/7.09; pa = 351°; sep = 0.943“, (2017, last precise; solid data)
345x:  easily seen as split 100% of time to two white stars of slightly dissimilar magnitude; above resolution limit
image below is from 2019.455

 

STF 2218 (17403+6341) mags 7.08/8.37; pa = 308°; sep = 1.476“, (2015.5, Gaia DR2; solid data)
345x:  split 100% of time to two whitish stars; averted vision aids visualization of the fainter secondary; above limit

STF 2403 (18443+6103) mags 6.25/8.35; pa = 278°; sep = 1.061“,  (last precise, 2011; solid data)
345x:  seen as just split 50% of the time; both stars are yellow with the much smaller secondary sitting a bit past the first diffraction ring; above resolution limit
There may be a number of observations for this one as it is part of the Sissy Haas Uneven Double Project

STT 369 (19071+7204) mags 7.82/7.91; pa = 8°; sep = 0.684“, (2015.5, Gaia DR2; solid data)
345x:  just split when seeing allows; both stars are yellowish-orange with secondary a bit smaller
460x:  easier to see as split; above resolution limit

MLR 12 (18293+8235) mags 8.90/9.12; pa = 222°; sep = 0.689“, (2008, last precise; data is old)
345x/averted vision:  mostly pointy
460x/averted vision:  much smaller secondary seen as resolved only 20% of the time—very difficult; right at resolution limit; separation re-measure needed

STT 312AB Eta (16240+6131) mags 2.80/8.20; pa = 143°; sep = 4.676“,  (2015.5, Gaia DR2; solid data)
345x:  secondary is a tiny speck of light well separated from the primary; held steadily in view on nights of better seeing; above resolution limit

Hercules
COU 107 (16169+1948) mags 9.02/9.61; pa = 113°; sep = 0.609“, (2009, speckle; data is old, scant)
345x:  very faint; merely a bit elongated; below resolution limit; important data point to assess faintness factor; re-measure of separation needed

STF 2107AB (16518+2840) mags 6.90/8.50; pa = 107°; sep = 1.443“,  (2015.5, Gaia DR2; solid data)
345x:  easily split; both stars are whitish and the secondary is quite a bit smaller than the primary (but not tiny); above resolution limit

A 350 (16540+2906) mags 9.47/9.61; pa = 144°; sep = 0.630“, (2019.542, own measure; considered solid because in line with 4th Int. Cat. trend)
345x:  possibly pointy (not resolved); faint!
460x/averted vision:  barely resolved when seeing permits with the secondary appearing just a bit smaller versus the primary; at resolution limit; important data point to set faintness factor

Image below is from 2019.542

BU 627A, BC (16492+4559) mags 4.84/8.45; pa = 40°; sep = 2.116“, (orbital estimate for 2019.4; system is opening; value is in line with last precise [2.06”] and Gaia DR2 [2.105”])
345x:  easily split; both stars are white and secondary is quite small; above resolution limit
Inverted image shown below is from 2017.501

BU 812 (16071+1654) mags 9.06/9.36; pa = 96°; sep = 0.73“, (2011, last precise; data may be incongruent with historical 4th Int. Cat. values)
345x/averted vision:  image moves past elongated to notched about 40% of time showing two similar magnitude, faint stars; a re-measure of both separation and delta mag is desired; considered a bit above resolution limit

A 228 (17063+2631) mags 9.31/9.88; pa = 13°; sep = 0.658“, (2019.553, own measure; system is opening)
345x/averted vision:  image is at the elongated/resolved border; discs are tiny—very faint!
460x/averted vision:  resolved about 50% of the time; a bit above the resolution limit
Note:  listed magnitudes are from Hipparcos, not Tycho
Image below is from 2019.533

HDS 2446 (17177+3717) mags 4.62/8.53; pa = 143°; sep = 0.918“, (2010, last precise; solid data)
460x:  split ~100% of time on night of very good seeing; adding an orange filter to the optical train causes the secondary to nearly disappear which explains the exceptional difficulty experienced imaging this object; above resolution limit

STF 2315AB (18250+2724) mags 6.57/7.77; pa = 115°; sep = 0.600“, (orbital estimate for 2019.4; solid data)
345x:  merely a bit oblong
460x:  moves past elongated to a snowman shape about 30% of the time—stars clearly of dissimilar magnitude; on border of resolved but never actually seen as resolved; appears to be just below resolution limit
Inverted image shown below is from 2017.512

BU 641 (18218+2130) mags 7.03/8.66; pa = 341°; sep = 0.78“, (2015, last precise; solid data)
345x:  moves past pointy to resolved about 10% of the time; secondary is much smaller
460x:  seen as split when seeing allows image to sharpen (~30% of time); above resolution limit

STF 2339AB, CD (18338+1744) mags 7.45/8.67; pa = 277°; sep = 1.482“, (2018, last precise; likely solid data)
345x:  easily split to show fine magnitude contrast pair with primary seen as white and secondary as light orange; above resolution limit
460x/averted vision:  secondary [CD] now appears elongated—it has a rho value of 0.492” and is known as WAK 21CD—a very nice bonus!

A 238 (18114+2519) mags 8.59/9.55; pa = 74°; sep = 0.632“, (2019.548, own measure)
345x:  persistently pointy
460x/averted vision:  moves past elongated to resolved 20% of time; secondary is tiny; at resolution limit
Image shown below is from 2019.548

A 2093 (18054+1624) mags 9.09/9.85; pa = 226°; sep = 0.642“,  (2008, last precise; data is old but considered solid)
460x:  very faint, elongated rod that presents as resolved perhaps 5% of the time; at or slightly below resolution limit

TDT 1042 (18461+1328) mags 8.85/9.65; pa = 274°; sep = 0.7“,  (2009, last precise; data is old, not solid)
345x:  merely point; stars are faint
460x:  sharpens to resolved from a rod shape about 10% of time; at resolution limit; re-measure of separation needed

STF 2084 Zeta (16413+3136) mags 2.95/5.40; pa = 112°; sep = 1.373“,  (grade 1 orbital estimate for 2019.211)
345x:  light orange secondary just touching bright white primary—beautiful!  Above resolution limit
Image shown below is from 2019.452

STF 2203 (17412+4139) mags 7.72/7.81; pa = 293°; sep = 0.757“, (2015.5, Gaia DR2; solid data)
345x:  just split to two white stars—not difficult; above resolution limit

Libra
STF 3090AB (15087-0059) mags 9.09/9.34; pa = 287°; sep = 0.627“, (2017, last precise; little corroboration from 4th Int Cat.)
460x:  elongated only; never resolved
627x/averted vision:  never moved past elongated; below resolution limit; not sure why this object is so difficult—a re-measure of separation is desired

I1269AB (15249-2322) mags 8.73/8.84; pa = 199°; sep = 0.654“, (2015.5, Gaia DR2; solid data)
345x/averted vision (best conditions):  resolved to two white stars of very similar magnitude about 30% of the time; at or slightly above resolution limit; important data point to establish minimum rho value for calculator

BU 225BC (14255-1958) mags 7.16/8.37; pa = 91°; sep = 1.285“, (2015.5, Gaia DR2; solid data)
345x:  split 100% of time showing the primary as white and the secondary as light yellow and smaller; above resolution limit; a beautiful triple with the AB pair designated SHJ 179 or H N 80

HJ 4756 (15197-2416) mags 7.90/8.27; pa = 242°; sep = 0.574“, (2015.5, Gaia DR2; solid data)
345x/averted vision:  moves past elongated to notched 50% of time (never resolved)
460x:  resolved 50% of time; discs are very small and appear similar in magnitude; a bit above resolution limit; important data point to establish minimum rho value for calculator

A 81 (15089-0635) mags 9.43/9.76; pa = 41°; sep = 0.68“, (2005, last precise; data is old and scant)
345x/averted vision:  rod only; stars are very faint
460x/averted vision:  moves past elongated to resolved at most 5% of the time; below resolution limit; re-measure of separation desired

Lyra
HU 1300 (19202+3411) mags 8.92/9.56; pa = 184°; sep = 0.74“, (2015, last precise; data is solid)
345x/averted vision:  mostly a single star, but possibly rod-shaped; faint!
460x:  at most rod-shaped (never resolved); below resolution limit which makes this object an outlier—further investigation warranted

A 703 (19072+4451) mags 9.01/9.28; pa = 189°; sep = 0.57“, (2010, last precise; likely solid data)
as yet unobserved; important data point to establish faintness factor for resolution calculator

BU 648AB (18570+3254) mags 5.34/7.96; pa = 243°; sep = 1.303“, (grade 2 orbital estimate for 2019.3)
460x:  small brightening apart from the primary that sharpens to a small disc that is seen as split 50% of the time
627x:  split 100% of time; secondary is much smaller, both stars appear white; above resolution limit

Have you observed or imaged any of these double stars?  I would love to hear of your endeavors with these objects.  Are there other, similarly challenging objects in these constellations that I have missed?  Let me know.

Nucleophile(Austin, Texas, USA), from an online thread entitled; 8 Inch Reflector Investigations. Part V: Corona Borealis, Draco, Hercules, Libra, and Lyra.

STF 2054AB

 

STF 2084 Zeta

 

STF 2084 Zeta

 

Nucleophile(Austin, Texas, USA), from an online thread entitled; 8 Inch Reflector Investigations. Part V: Corona Borealis, Draco, Hercules, Libra, and Lyra.

Excellent as always Mark!

Here are some of my observations from your list, plus a few others you might try:

Cou 610 AB: 8″ 667x: Notched/snowman at best moments.  B definitely fainter and almost blue.  Very faintly split, looks like a blue appendage.  20″ diffraction is too messy.

STF 2107 AB: !! 12.5” This was a CDSA plot find, didn’t expect it to be special.  Yellow and orange pair, very close ~1.5″, 1 delta mag.  Very pretty.

STF 2315 AB: 12.5” 553x.  Near contact / overlapping disks, 0.5 delta mag.

BU 641 AB: 12.5” 553x. !! Extraordinary!  Moderately bright A and much fainter B, <1″ separation.  Seeing needs to still.

STF 2339 AB-CD: 20”: 533x: White and dull white B. Close but well separated, ~1″ [AB-CD seen. AB is Hu 322 1 delta mag 0.2″, not noticed]

STF 3090 AB: 12.5” Notched to hairline split at the best moments. Faint pair, tough. Seeing not good enough to go above 553x. [AB seen; AC fainter and wider.]

BU 648: 8″ 333x: 3 delta mag, at first diffraction, needed critical focus and seeing.

OTHERS:

Met 9: 8″ 205x nothing.  8″ 410x suspect elongation.  667x see a fleeting, bluish point just outside of first diffraction ring.  A is light yellow orange and bright; 2 delta mag. to B.  A feels elongated / egg shaped.  At 20″ and 667x the seeing is too messy though there is a knot in the diffraction where I had noticed the point with 8″.  Strong feeling A is elongated.
12h 54m 39.98s +22° 06′ 28.8″ P.A. 51 sep 1.7 mag 5.70,7.77 Sp F8V+M2-3V dist. 33.85 pc (110.42 l.y.)

STF 1967 = Gamma CrB: Definite mis-shape, oval to egg.  8″ 667x.
15h 42m 44.57s +26° 17′ 44.3″ P.A. 104.6 sep 0.22 mag 4.04,5.60 Sp B9V+A3V dist. 44.78 pc (146.07 l.y.)

STF 2289: Just split in 20″ at 205x, but flaring. 333x had messy diffraction. 8″ mask at 333x gave clean disks, split, ~0.7″. Dull yellow and yellow-red colors.

18h 10m 08.69s +16° 28′ 35.0″ P.A. 215.3 sep 1.24 mag 6.65,7.21 Sp A0V+G0III dist. 263.85 pc (860.68 l.y.)

STT 359: !! Kissing 8″ 333x, hairline split 667x. 20″ too diffracted. Near equal white A and bluish white B.
18h 35m 30.40s +23° 36′ 19.9″ P.A. 3.7 sep 0.75 mag 6.35,6.62 Sp G9III-IV dist. 144.3 pc (470.71 l.y.)

A 260 AB: 20″ 667x: At 8″, small and faint suspected split at 333x: 8″ 667x stars are hazy. At 20″ 667x got a clean wide split two hard paints of stars.
18h 57m 34.07s +32° 09′ 20.2″ P.A. 244 sep 0.8 mag 9.17,9.60 Sp A0

STF 2422: 8″ 333x: Excellent hairline split at 333x with 8” mask. Near equal white stars. Picked them out in a crowded field, suspected elongation right away, split with seeing as I centered it in eyepiece, and from then it was a steady split
18h 57m 07.83s +26° 05′ 45.1″ P.A. 68 sep 0.8 mag 7.93,8.25 Sp A2IV dist. 156.25 pc (509.69 l.y.)

AGC 9 AB = Sulafat: 8” 533x: B star immediately picked out of A’s glow like a piece of debris suspended in the explosion, or a planet hanging in the halo.
18h 58m 56.62s +32° 41′ 22.4″ P.A. 307 sep 13.5 mag 3.24,12.10 Sp B9III dist. 190.11 pc (620.14 l.y.)

HO 92 AB 20″ 667x: ! Beautifully well split, had an instant of perfect images. White pair near equal.
19h 00m 59.89s +32° 33′ 11.6″ P.A. 40 sep 1.3 mag 10.59,10.85

COU 1156 AB 20″ 667x: ! Near qual small and at best moments a clean split, still, just nice points. great star.
19h 00m 34.25s +33° 01′ 24.8″ P.A. 111 sep 0.7 mag 11.14,11.25

STF 2461 AB = 17 Lyr: 20″ 667x: ! Huge delta mag. B is obvious in 20″, though A’s diffraction was horrible. Used 8” mask to clean it up but the B star momentarily disappeared, though I could eventually pull it back out with seeing and critical focus. 4 delta mag.
19h 07m 25.58s +32° 30′ 06.2″ P.A. 281 sep 3.2 mag 5.26,9.10 Sp F0V dist. 41.58 pc (135.63 l.y.)

mccarthymark(San Francisco, California, USA), from an online thread entitled; 8 Inch Reflector Investigations. Part V: Corona Borealis, Draco, Hercules, Libra, and Lyra.

I like using my 105mm APO on double stars over my larger scopes just because it gives nicer images even when the seeing is below average.  I still get nice round stars but the whole image kind of bounces almost like my clock drive is making it bump up and down a little.

An 8″ scope will be affected 4 times as much as a 4″ on the same night, so in this case aperture doesn’t rule in below average seeing.

If I am going specifically after doubles, I tend towards my 10 inch Dob rather than any of my refractors.  One reason is for it to perform it’s rock solid best, I need to set out up before sunset and run the fans for considerably more than an hour.

If the seeing is on the good side and I started with a 4 or 5 inch, I’m stuck.  

For closer doubles, maybe 1.4″ or closer, the 10 inch provides wider splits under most circumstances because it’s Airy disk is so much smaller. A 1.14″ double is a Dawes limit split in a 4 inch, in the 10 inch it’s a wide split and I’m not fighting both the large Airy disk and the seeing.

I’m not sure about your factor of 4 in terms of the effect on the image. I am not looking so much for a pretty image, I’m looking for closer splits. Antares is usually a challenging split in a 4 or 5 inch but last year I made the split in my 22 inch with Antares quite low on the horizon, no way in a small scope.

It wasn’t pretty but it was very wide, bright and apparent. It made me realize just how small the airy disks are in a scope that size.

With any scope but a larger scope in particular, the outer seeing aberrated region can as an extended object while it surrounds the region where the airy disk is brighter. Cranking up the magnification can increase the contrast by dimming that outer region.

Jon Isaac( San Diego, California, USA), from an online thread entitled Effects of Bad Seeing: Double Stars

This was my second dark site session with my new telescope.

A week before, I had to cut the session short as humidity became unbearable – spider and shroud started dripping.
I want to share my impressions of this device now that I had a full session.

 

Logistics first.
This is not a small scope so I got a folding aluminum ramps for loading it. This way, I can load the scope alone and it is faster than loading my SW 12″ collapsible.
just need to make sure that mirror box is tilted a bit so the bearing will not hit the car ceiling.

Truss and shroud are light and have plenty of room.
For a 20″ monster, the process of loading is easy enough.
If not totally lazy or must, the scope can be loaded/unloaded without ramps.

The road to the dark site is about 2.5 hours drive. I have been making this trip every month for over a year now and love the drive.

I was the first on site, about an hour before dark.
Unloading was simple enough and once everything was out of the car, I went to assemble the scope

Assembly is quick, Truss to mirror box, fasten the bolts, UTA on Truss, fasten the bolts and then the shroud.
This takes few minutes and is easy, just as Ryan show in his Youtube channel.

For collimation I use the Farpoint 2″ collimation kit – laser and cheshire.
Even after 2.5 hour drive, last part of it is off-road, collimation did not drifted by much.

The entire process of assembly + collimation takes about ~20 minutes.
With camp set – tent, table chairs, I still had time to dress for the cold before total darkness.

I was lucky to see the gathering of Venus, Moon and Jupiter with Saturn watching from above.

That was an amazing sight!

 

Observations:

First I revisit the Vail nebula.
Eyepiece – Nagler 31mm filtered with O-III
Started with the Western part of the nebula from the tip through Cy52 to its bottom part. The amount of details was insane.
The Eestern part as equally stunning.

The central part of the nebula was nicely visible.

Tonight’s plan was to go through objects in Cassiopeia, Perseus, Andromeda, Orion and Ursa Major.

Double cluster fits nicely into the FOV of the Nagler 31mm. Very sharp image.
Raising magnification a bit, still could see both clusters within view.
Next came the Owl cluster, M103, NGC 663 and more.
Pacman nebula was also nicely visible, I will have to revisit this object to figure out more details.

I did a quick detour to view M15. This cluster is magnificent! raised magnification to 135 and the cluster could be resolved nicely.
With magnification of over x200 which is reserved for such objects, I could easily distinguish stars almost to the core.

Andromeda Galaxy showed two dust lanes, one very distinct and the other is fainter. I never saw so many details in the arms before.
Both companions – M110 and M32 also fit the FOV.

Pinwheel Galaxy, another showpiece object also provided much details.

In Orion, I saw the bubble nebula for the first time.
M42 is majestic as ever, all the details are just fantastic, the nebula is closing full circle, wings full of details. With filters, different details emerge.

The 20″ collects so much light that even a cellphone camera could yield details (I had to try…)

Horsehead nebula was not visible when it was 30-40 degrees but when reaching over 50 degrees altitude, provided a lots of details.
The nebulusity from Alnitak towards HD 37806 was visible with the horse interrupting it like a finger obscuring the view.

Last area covered was Ursa Major – galaxy hunting.
Finding galaxies with this huge field of view is fun and easy.

This session yielded many objects, over 50 were documented, many were not viewed enough and will be revisited to get more details.

My impressions so far:

I am very happy with my new telescope.
The difference in view from my 12″ is everything I expected and more, some objects are actually visible and others show so much more details.

Views are wide, crisp and sharp, especially when conditions allows.
Transportability and the ability to handle it by myself is exactly why I opted for NMT in the first place.
Mechanically this is a wonderfully constructed device. Movement is smooth in both axis but firm enough not to shift when switching eyepieces.
Balance is the same without eyepiece or with Paracorr-2 + Nagler 31mm. I guess Binoviewer will require some counterweight – Ryan provided rails for counterweight, just in case.
Collimation lasts in full movement range and during the session – I did not check, but felt no view degradation – will test it on the next session.

Scope Basking in the morning sun after a long night

ilan Shapira( Israel), from an online thread entitled; My NMT 20″ f/3.3

Got back out for an hour or so and tried out my higher powered plossls. Seeing was not great and I’m under white zone skies with limited sky to point at from my driveway but I make it work. I can tell the scope is a bump up from my ST80 with the higher powered eyepieces. To my newb eyes collimation appears good. Stars weren’t exactly pinpricks at high power but they’re round and turn into nice round donuts in and out of focus.

Took a look at a dimming beetleguese, Uranus with I think a hint at its moons. The Pleiades looked great back down with the 32 plossl.

M42 looked better than I’d ever seen it at all powers. And it looks spectacular to my eyes with my $13 UHC filter.

It’s definitely a different experience looking through the eyepiece on this reflector as opposed to my mak and my refractor. Just a bit higher at most views than is perfect viewing on my camp stool, but being able to rotate the tube in the rings brings it to an accessable height.

(If this post would have been more appropriate in the beginner forum I apologize.)

Tannhauser Gate, from an online thread entitled, First Light with a cheap 130/650/f/5

I like 130 mm F/5 Newtonians. If the optics are decent, they’re the closest thing to a budget 4 inch apo you can buy.

The focuser appears to be a Crayford, that’s a good thing. It looks like a 2 inch Orion focuser,, there’s no adapter?

Have fun..

Jon Isaac( San Diego, California, USA), from an online thread entitled, First Light with a cheap 130/650/f/5

Actually it goes a little deeper than any 4 inch Apo and resolves significantly closer double stars(down to 0.9″) in the hands of experienced observers and good seeing conditiions.

Mr Hardglass

That’s a sharp looking scope.,I love my 130.,it’s my most used scope because it puts up great views and is easy to carry out and be viewing.,cheers.

Clearwaterdave,(Western Maine, USA), from an online thread entitled, First Light with a cheap 130/650/f/5.

 

SteveG( Seattle, Washington, USA), from an online thread entitled: Want a Planet killer: suggest some

The slower the scope, the better. I had a Discovery 10 F5.6 that gave great planetary views, but it couldn’t compete with my 8” F9 when it came to high power views. With 3.5 mm and 5mm eyepieces, I can comfortably view objects at high power all night long. And not once have I ever observed a planet with my 8” and thought, the image isn’t bright enough. Barlows are useful with fast scopes, but a 2x barlow will not perform nearly as well as a scope with twice the F ratio.

Galicapernistein, from an online thread entitled: Want a Planet killer: suggest some

bobhen, on 17 Jan 2020 – 1:40 PM, said:

It’s all about the quality of the primary. Whether its F5 or F8 doesn’t matter. If the mirror is 1/10 wave it is 1/10 wave.

 

 

I think closer to 1/8 limit

But it has to be real. Regardless of the manufacturer and its advertising promotion.

a  I, from an online thread entitled: Want a Planet killer: suggest some

I would think a 20″ Ostahowski f/3.4 would be a fine instrument for planetary observation once cooled and well collimated… 20″ of well figured aperture would pretty much kill anything you throw at it.

Volvonium(Long Beach, California, USA), from an online thread entitled: Want a Planet killer: suggest some

Not really sure what to suggest but my 25″ kicks butt on the moon and planets. Barring going for such a big scope my 8″ f/9 Parks newt on a platform is a close second.

Keith Rivich(Cypress, Texas, USA), from an online thread entitled: Want a Planet killer: suggest some

I have an f/4.5 16” Ostahowski mirror, and also an 8” f/7 by Steve Lee. Both appear excellent mirrors but the 16” slam dunks the 8” on everything. As it should. Every time I think of building a planet killer…like, say, a 10” f/7 or whatever, I remind myself I already have one.

Oberon(Hunter Valley, NSW, Australia), from an online thread entitled, Want a Planet killer: suggest some

I have a 6-inch F/8 that is a planet killer for a small telescope, but the 8-inch SCT, 10-inch F/4.5 an 15-inch F/4.5 Dobs also do very well on the planets too when the seeing is good. I spent many hours looking at Mars, Jupiter and Saturn with my reflecting telescopes, and imaging them with the 8-inch SCT. The best views though came with my Dobs though, especially the 15-inch. That said, the 6-inch is no slouch and has excellent optics, the primary mirror was made by Meade back in the 70’s. The 10-inch also has a Terry Ostahowski mirror, and the 15-inch has a primary mirror made by Optic Wave Labs.

Achernar(Alabama, USA), from an online thread entitled, Want a Planet killer: suggest some

A well figured 10″ as has been mentioned. Some of my best views of Mars were with a 10 f/5.4. Saw dark volcanoes on Mars years ago with 8″ f/7. Mars was high up, seeing was spectacular and scope was working well at 600x. My eyes were a bit better, too.

Mike Spooner

Any well built Newt is a brute for planets in my super steady seeing. Fast or slow is fine. Old school 8″ F/8 Cave or other makes also make great planet scopes as well as used Starmaster Dobs at around F/4.3.

CHASLX200(Tampa, Florida, USA), from an online thread entitled, Want a Planet killer: suggest some

On nights of fair to average seeing, I will be relying on my TSA 120; on good to excellent nights it will be my new-to-me Teeter- Zambuto 10” f/5. It was damaged in shipping is still in limbo awaiting settlement from the shipper.

Skyranger(Prescott, Arizona, USA), from an online thread entitled, Want a Planet killer: suggest some

Custom designed Newton:

Obstruction less than 20% = planet killer or APO killer

Cameras for planets: ASI / QHY – 290 / 224 = 6 – 7 mm diagonal.

 

Newton 12″ F/5.3  (300×1600)
Primary Mirror: 303 mm
Secondary Mirror: 50 mm
Obstruction: 16.5% (Obstruction surface: 2.72%)
Illuminated diagonal: approx 9-10 mm

 

Newton 12″ F/5  (300×1500)
Primary Mirror: 303 mm
Secondary Mirror: 50 mm
Obstruction: 16.5% (Obstruction surface: 2.72%)
Illuminated diagonal: approx 7-8 mm

 

Newton 10″ F/6.4 (250×1600)

Primary Mirror: 254 mm
Secondary Mirror: 40 mm
Obstruction: 15.7% (Obstruction surface: 2.48%)
Illuminated diagonal: approx 10-11 mm

 

Newton 10″ F/6 (250×1500)
Primary Mirror: 254 mm
Secondary Mirror: 40 mm
Obstruction: 15.7% (Obstruction surface: 2.48%)
Illuminated diagonal: approx 8-9 mm

 

Newton 10″ F/5 (250×1250)
Primary Mirror: 254 mm
Secondary Mirror: 45 mm
Obstruction: 17.7% (Obstruction surface: 3.14%)
Illuminated diagonal: approx 7-8 mm

 

You can do the calculations on this website:

 

https://stellafane.o…b/newt-web.html

cabfl, from an online thread entitled, Want a Planet killer: suggest some

My 8″ f/8. Royce primary, Protostar quartz secondary. After midnight, when the seeing settles and the scope temperature has fully equalized.

K15CAW, from an online thread entitled, Want a Planet killer: suggest some

I had a 6” F8 Discovery dob that had an excellent mirror. But my SW 100 ED was close enough that I sold the dob for the convenience of the refractor. But going from a 6” F8 to an 8” F8 or 9 dob puts you into an entirely different league. I would put my 8” F9 against any 5” APO refractor. That said, I still want a 5” APO refractor.

Galicapernsitein, from an online thread entitled, Want a Planet killer: suggest some

obhen, on 17 Jan 2020 – 7:38 PM, said:

No place in the United Sates will a 20-inch telescope ever resolve to its full potential.

 

On few nights and in the best locations like south FL. a 12 to 16-inch will have a chance but in most locations just getting sub arcsecond seeing is rare. And not only do you need that seeing but the planets need to be high or at zenith or the seeing will be compromised even more.

 

For example…
“At the William Herschel Telescope site in the Canary Islands, even this superb viewing location (second best in the northern Hemisphere) has many nights of relatively poor seeing: the distribution is positively skewed, and at this excellent site, a 10-inch telescope will be seeing limited on 9 out of 10 nights.”

 

Bob

 

That’s really not the question. A large scope maybe seeing limited but still outperform a smaller scope. 

 

The Dawes limit and the Rayleigh criterion are not the appropriate measures to determine the resolution/ seeing limits. 

 

In 1 arc-second seeing, a 10 inch will be seeing limited but dramatically out perform a 5 inch. 

 

Think about airy disk diameters and overlapping disks.. 

 

This my planet killer..

 

Bill Jensen, on 19 Jan 2020 – 6:31 PM, said:

Zambuto has an in stock 8 inch f/7 that is listed on his website. Those don’t come up that often, and may be a nice solution to your planetary viewing desires.

This 

 

I have a quartz Zambuto 8″ F/7 on order that should be ready in about a year or so. I would like to find a lightweight scope to house the mirror and then possibly put it on an equatorial platform. 

starzonesteve(Central Alabama, USA), from an online thread entitled, Want a Planet killer: suggest some

I got lucky on used parts on AM that included a Zambuto 8″ F7 quartz. It’ll clobber any 6″ refractor on the planets, and is basically up and running in a few minutes as the substrate doesn’t have temperature equilibration issues.

The 8″ is so good that I’ve decided to replace my 12.5″ F5 Zambuto pyrex with one of his quartz mirrors. I’m hoping it’ll be ready in the summer.

areyoukiddingme, from an online thread entitled, Want a Planet killer: suggest some

CHASLX200, on 18 Jan 2020 – 12:11 AM, said:

Any well built Newt is a brute for planets in my super steady seeing.  Fast or slow is fine.  Old school 8″ F/8 Cave or other makes also make great planet scopes as well as used Starmaster Dobs at around F/4.3.

 

Most mass made Newts the last 20 years just don’t do it for me.

+1  I have a 12.5” and an 18” Starmaster, both with Zambuto mirrors, and on the best nights they are planet destroyers.

turtle86, from an online thread entitled, Want a Planet killer: suggest some

Galicapernistein, on 21 Jan 2020 – 4:12 PM, said:

A high F ratio is inherently better for high power views. A slow scope with excellent optics will give better views of planets than a fast scope with equivalent optics. This is a fact that owners of fast scopes need to accept.

No, it is not a fact, and it is quite wrong, so we will not accept it.  What Jon said above is correct.

The laws of optics and physics don’t lie – they will give the same view, assuming similar quality eyepieces and equilibration and the the eyepiece is designed for the faster cone, not including some miniscule effects (which are almost always overblown) from a larger secondary in the faster scope.  This is easily overcome by adding a small amount of aperture if one wishes.  Then the slightly larger fast scope wins.

Let’s not ban certain terms, (i.e. planet killer) let’s educate people about where they came from and why they are misleading or wrong.

My planetary scope?  My 20″ f/3.0.

Mike Lockwood,from an online thread entitled, Want a Planet killer; suggest some

Galicapernistein, on 21 Jan 2020 – 4:45 PM, said:

So someone starting out in astronomy who wants to see Saturn’s rings should buy a 6 inch F5 because they’re so much more convenient than an F8? I don’t think so.

Think outside the box.. 

A 6 inch F/8 is 48 inches long, an 8 inch F/6 is 48 inches long, a 10 inch F/5 is 50 inches long.  They’re the standard dob configurations.. 

 

I can tell you which one provides the better planetary views… 

P.S.:  A 6 inch Newtonian is not what I consider a planet killer.  A good scope but not enough aperture.

Jon Isaac ( SanDiego, California, USA), from an online thread entitled, Want a Planet killer; suggest some

A slow scope will give better high power views than a fast scope with equivalent optics. It would be nice if we could accept that fact without bringing in these other factors.

 

I accept that a slow scope with equivalent optics will provide slightly better views than a fast scope.  

But it would be good if you would accept that those other factors are far more important in providing killer planetary views than the focal ratio.  

Today, a slow scope that provides the planetary views possible with a large aperture, fast scope is impractical.  

It is about the views.. 

Jon Isaac (SanDiego, California, USA), from an online thread entitled, Want a Planet killer; suggest some

I’ve gotten many extraordinary views of the moon/planets with an optically excellent 10″ f/5 dob. The whole idea of some longish newt or hyper-expensive APO as the only planets killers has one foot in mythology and the other in the grave.

Largish aperture of high quality is your best bet.

Nirvanix(Medicine Hat, Canada),  from an online thread entitled, Want a Planet killer; suggest some

Itha(Bend, Oregon, USA), from an online thread entitled, Want a Planet killer; suggest some

cooke, on 24 Jan 2020 – 3:16 PM, said:

I’m in the camp of thinking that a planet killer is any scope, regardless of f-ratio, type, or configuration, that has the capability of delivering a killer view of the planets.  As others have said, realizing that view has more involved than just the telescope itself; managing thermal issues, seeing, collimation, viewer experience, etc. all factor into what is seen but reducing the variables to just the telescope itself, it could be anything of sufficient aperture.  I do think that while smaller scopes can give excellent images of the planets for their size, if you don’t have at least 6″ of aperture and preferably 10″ of aperture, you are unable to realize the resolution available on the best of the best seeing nights.  Having said all that, my best views of Jupiter and Saturn ever were with a 18″F3.75 Starmaster.  I think the additional aperture also helps a lot when using high magnification to see the smallest lowest contrast details.  The additional light just helps make the difference even if the larger aperture is seeing limited.

When I say a high F ratio is better for high power views, I should specify (and I will from now on) that I’m talking about smaller newts. Bigger mirrors can obviously compensate for many issues by sheer resolving power. An 18” F8 might provide better views, but the atmosphere will only allow so much power, and an 18” F8 would require a ladder I wouldn’t want to climb. The bigger exit pupils they provide are a definite improvement over smaller scopes. There’s no arguing that a big, fast newt packs a lot of performance into a relatively small package, and for serious galaxy hunting they can’t be beat. 

Galicapernistein, from an online thread entitled, Want a Planet killer; suggest some

scooke, on 24 Jan 2020 – 3:16 PM, said:

I’m in the camp of thinking that a planet killer is any scope, regardless of f-ratio, type, or configuration, that has the capability of delivering a killer view of the planets.  As others have said, realizing that view has more involved than just the telescope itself; managing thermal issues, seeing, collimation, viewer experience, etc. all factor into what is seen but reducing the variables to just the telescope itself, it could be anything of sufficient aperture.  I do think that while smaller scopes can give excellent images of the planets for their size, if you don’t have at least 6″ of aperture and preferably 10″ of aperture, you are unable to realize the resolution available on the best of the best seeing nights.  Having said all that, my best views of Jupiter and Saturn ever were with a 18″F3.75 Starmaster.  I think the additional aperture also helps a lot when using high magnification to see the smallest lowest contrast details.  The additional light just helps make the difference even if the larger aperture is seeing limited.

I agree. I have an AP 130 GT, and it’s as good as a 5″ apo can get. It certainly gives great planetary views, but it simply can’t compete with my 18″ Starmaster in terms of resolution, at least where I observe.

turtle86, from an online thread entitled, Want a Planet killer; suggest some

If i had to have one last planet scope, it would be a 20″ F/6 Dob.

CHASLX200(Florida, USA), from an online thread entitled, Want a Planet killer; suggest some

Newtonians of 8-12.5″ aperture are the most cost effective. I agree with others that perhaps the easiest/cheapest way to a planet killer is to buy a mass-manufactured Dob and have the primary refigured. First, though, you may want to replace the secondary with a high quality mirror from the likes of, say, Antares and see if you are happy. The MTF of any obstructed scope degrades significantly when the diameter of the secondary minor axis exceeds 20% the primary diameter. Thus, you will want such a small secondary, which if you also want a 1 deg or so field with only minor vignetting for DSOs, means f/4.5 or greater. So a 12.5″ with f/4.5 or greater can yield fabulous planetary detail. However, the mirror must be supported properly (check with the freeware program PLOP), the mirror must be allowed to thermally equilibrate (I set mine up at dusk … a fan is a good idea too), and collimation needs to be spot on. Incidentally, mass manufacture SCTs have central obscurations of roughly 35% so planetary contrast aperture-for-aperture is less than with a Newtonian.

dhfergusson(Pleasanton, California, USA), from an online thread entitled, Want a Planet killer; suggest some

Personally I use a 200mm F6 Quartz newtonian. I’d love to go bigger, but I also don’t like the idea of ever moving something bigger outside of my observatory, so for non-obs scopes, I keep them portable enough. I also do not like dob-bases due to the materials, I’d want it to be all metal. I’m in Florida. Florida is not friendly to non-metal and I’m not about to baby some cheap particle/ply or whatever cheap dobs are made of, and I’m not spending top dollar on a custom dob. I’d rather have a beefy alt-az and keep it simple and fast with the 8″ for now. Maybe one day I’ll get a metal dob frame and go 16″. But that’s a big maybe.

MalVeauX(Florida, USA), from an online thread entitled Want a Planet killer; suggest some

For me the #1 priority is an accurate figure – I’ve been satisfied with Newtonian planetary views from 6″ up to whatever. The primary is the building block at the bottom of the wobbly stack, IMHO. The secondary is next (and often a problem for critical viewing) but smaller sizes can be replaced with less hassle and financial impact than the primary. Most of the remaining problems fall into what I would classify as mechanical/environmental effects, i.e. thermal, collimation, seeing, mounting, etc.

So pick a size, get the primary right and work from there. My personal opinion concerning f/ratio and secondary size is they can be considered for 6 to 8″ scopes as they are comfortable at f/10 or f/7 (for my height when Dob mounted). For larger scopes I like more comfortable f/ratios. With Paracorrs, modern eyepieces and collimation knowledge available having mitigated some of the old concerns, then we’re back to the quality of the objective – still the base of the wobbly stack for me.

Mike Spooner, from an online thread entitled Want a Planet killer; suggest some

Late to the discussion but here are mine, a TEC 200ED and my Parallax/Zambuto 11″ F7.  Rather than compete, they compliment each other.  

Around here, the seeing rarely supports an 11″ aperture, so the TEC gets used more often.  When the seeing does support a larger aperture, I can get the Newt unbagged, the mount sync’ed and observing in under 10 minutes.  

For me, planetary viewing demands exceptional optics (and seeing!!) but also a “comfortable’ viewing experience, which, again, for me, means being seated or standing comfortably.  I can do both with both scopes, making long sessions at the eyepiece a pleasure.

Also for me, I’m just addicted too my bino-viewers, especially for solar system objects.   I just see more and I find the viewing experience much more comfortable than mono-vision, and with my Denk power switch system, I can cycle through three different magnifications instantly.

For me, an excellent planetary newt has to have the following:

1. 8″ – 12″ aperture and I prefer F6 or slower focal ratios

2. Exceptional optics (including the secondary) that are smoooooth, with good coatings.

3. Central obstruction under 20% (pretty easy to do really, especially in slow scopes)

4. Excellent build quality which includes easy, precise collimation with the ability to keep collimation when pointed anywhere in the sky over the entire night and an excellent focuser.

5. An excellent thermal management system, which typically includes a BL fan.

6. Easy use of bino-viewers

7. A rotating tube if I use a GEM, for easy, comfortable eyepiece positioning and the ability to put my body down wind of the aperture.

Can’t wait for Mars this year!

JeffB, from an online thread entitled Want a Planet killer; suggest some

First light on my UVenus filter tonight!

Very nice photo. That’s a pretty awesome outcome for first light on any device.Thanks for sharing.

I hope I’m not out of line in asking: Who is the manufacturer of your 8″ Newt and is the 3100mm your OT focal length?

jodemur(East Michigan, USA), from an online thread entitled, Venus in UV – 8″ Newt + ASI183MM

jodemur, on 26 Jan 2020 – 1:16 PM, said:

Who is the manufacturer of your 8″ Newt and is the 3100mm your OT focal length?

 

It is a Celestron Starhopper, one of the newer metal tube ones so a standard Synta product. They make pretty solid f/4.9 mirrors all the time so I figure f/6 should be even better. It’s a 1,200mm stock focal length but I measured the pixel width of Venus to calculate that my 2x Orion Shorty Barlow is giving me about 2.6x magnification.

jragsdale(Idaho, USA), from an online thread entitled, Venus in UV – 8″ Newt + ASI183MM

I was going to post in “what did you see with your classic ” but its large enough to be alone

1 both scopes are in great shape

2) both scopes mounted on lxd55 mount for better track

3) seeing was very very good and moon was high up near zenith

rv6 had 2x barlow

ed4 some shots with 2x barlow and some not

 

highfnum(North East, USA), from an online thread entitled, redo classic shootout edmund 4inch vs criterion RV6

Cool images eh? Like I says in part I, I dinnae trust an over zealous sketcher, ken.

Mr. Hardglass.

so both scopes did a great job

however RV6 does show more detail

IMHO it looks like I picked up some of rille with ED4 – if correct that’s a new record for me for scope size

ed4 had more trouble with smaller circular features

some folks in past have said that a 4 inch refractor has same capability as 6 inch reflector

if its a good 6 inch – I say no

highfnum(North East, USA), from an online thread entitled, redo classic shootout edmund 4inch vs criterion RV6

I purchased the Skywatcher 130mm PDS a few days ago. Shipping took about 4 days from the U.K. and was about 50 bucks. The diffraction pattern star test showed essentially identical in and out of focus diffraction patterns, a very nice optic. Here is an LRGB image of the globular cluster M15 taken last night.

L=R=G=B= 125 seconds. Taken with a SBIG ST-402MM CCD.

 

grafton(Houston, Texas, USA), from an online thread entitled, Skywatcher 130 f/5 PDS – mini review

I tried out my Skywatcher 130 PDS on the moon a few weeks ago. A 3x barlow and an ASI120mm video camera was used. When I first received the scope a few months ago I did a star test and noted that the optics were very good.

 

The crater Copernicus

 

 

 

The crater Clavius

 

grafton(Houston, Texas, USA), from an online thread entitled, Skywatcher 130 f/5 PDS – mini review

From my experience, a fast 12″ dob can have very good planetary images.

“Killer” planetary is subjective I guess but my inclination would be to go for aperture, even from an urban observing location.

Right now I don’t have a scope but I’m considering either a 10″ or 12″ dob which would be used mostly for lunar/planetary under city skies.

My main issue is that I don’t like the tiny exit pupil that comes from using a small refractor at high power … but a 12″ newtonian is just cruising at x200.

John Anderson, from an online thread entitled: Want a Planet killer-suggest some

Mike Spooner, on 17 Jan 2020 – 11:41 PM, said:

A well figured 10″ as has been mentioned. Some of my best views of Mars were with a 10 f/5.4. Saw dark volcanoes on Mars years ago with 8″ f/7. Mars was high up, seeing was spectacular and scope was working well at 600x. My eyes were a bit better, too.

 

Mike Spooner

Ask Mike if he has any planet killers for sale. I looked through his 6″ F10 a few years ago…OMG! Also, he has good seeing in the SW.

Acocran(Sonora, California, USA), from an online thread entitled: Want a Planet killer-suggest some

My killer would be a reflector, made by Ed Grissom, like the one found in ‘Best of reflectors thread’, ‘refractor vs reflector ‘, by Daniel Mounsey. Any size would probably be fine, but his 13″ sounds to be just about right !

Subaru45(central Wyoming, USA), from an online thread entitled: Want a Planet killer-suggest some

 

GeraldBenton(Wilton, NC, USA), form an online thread entitled, AWB OneSky first light.

Well there is about 500 of us in the OS thread that will agree with you.,This little scope can do a lot.,Mine gets much more airtime than any of my other choices..

I just had mine out moonin with a new 17.5mm Morfeus eyepiece and the OS showed more craterettes than my AT102ED., go figger.,cheers

clearwaterdave(Western Maine, USA), form an online thread entitled, AWB OneSky first light.

Seeing was fantastic this evening right around sundown so decided to see what Venus had to offer in UV. Maybe my best details in Venus upper cloud features yet! I also captured a near infrared (685nm) version as well. Using the IR as red, UV as blue, and a mix of the two for green, it makes an interesting albeit false color representation of the planet.

 

jragsdale(Idaho, USA), from an online thread entitled; Venus in UV – 8″ Newt + ASI290MM

Unless the seeing is abysmal, a larger telescope will always show finer detail than a smaller one with equivalent optical correction. My driveway typically has seeing that’s on the order of 3 arcseconds, and my 15-inch shows better planetary detail set up right next to the 10-inch. And the 10-inch similarly does better than my 4-inch refractor.

The quoted seeing is typically FWHM (full width half maximum) of a profile of a star’s brightness based on images with long exposures, so it’s not good at telling an observer what the instantaneous seeing is. Veteran lunar/planetary/double star observers know to wait for moments of good seeing. The FWHM value may be 3 arcseconds, but during those brief intervals, it’s sub-arcsecond.

Tom Polakis(Tempe, Arizona, USA), from an online thread entitled: Arc second seeing

Hi, guys! I used an excellent 12.5-inch Cave Astrola Newt for about a decade and stared at stars directly and with knife-edge to scrutinize wavefront and Airy Disc. Thousands of hours of imagery and hundreds of hours staring at guide stars or KE patterns. I’d enjoy reasonable Airy Disc (tight core and one pretty stable ring) maybe 10% of the time. On great nights that would hold in, sometimes for up to a half-hour straight  And that is indeed in the neighborhood of the half-arc-sec you mention. Keep in mind, that is a very squishy benchmark, depending on the behavior of both your telescope and the atmosphere. The BIG scope 0.2 arc-sec transitions into the realm of ~wishful thinking~ even for the professionals. They are just as prone to exaggeration as we amateurs are… possibly more so.

We were testing/scrutinizing a 12-inch imager for professional use, out in the lot aimed at a distant cell tower. Crummy atmospherics, sunny summer day, terrible thermals occasionally calmed by passing benign breezes. I put a beamsplitter in there and watched real-time video, so I could snap the shutter, whenever the image looked sharper than average. (Technique I had learned for improved stats on lunar and solar imagery). We collected hundreds of “select” images, and then went inside, to sift thru for the best ones. And, something rather amazing happened — anticipated, but still surprising. A few of the select images manifested half-arc-sec “perfect” resolution. I already knew that the lens wavefront was crummy, but the explanation goes something like this: If the system’s Zernike wavefront is badly-aberrated but smoothly-so (aka continuously differentiable) then at times (rare times) the atmosphere will improve (rather than degrade) the wavefront presented to the image. So, with sufficient (large) # of short-exposure snapshots, a few will be “diffraction-limited”. 

Most of my assigned metrologies were spaced-based imagers. So, it is indeed true that an e.g. “Hubble-Class” big scope will and must resolve ~1/20 arc-sec to be considered ready to launch. Anything less is deficient. And that’s because the atmosphere is no longer the limiter.  

 

Tom Dey( Springwater, New York, USA), from an online thread entitled: Arc second seeing

JimP, on 27 Feb 2020 – 11:28 PM, said:

In terms of telescope resolution and planetary detail, I may have this wrong but it seems somewhere I read that the very best seeing conditions would be something around 0.4 arc seconds. Is this about right? If a 12” inch telescope has the ability to resolve approximately 0.4 arc seconds does this mean anything larger than 12” inches will show a brighter image but one is not likely to have seen conditions that will allow any finer detail to be seen. I know there are those of you out there who understand this far better than me so I await your thoughts.

Jim

Theoretical limits aside my 25″ blows away my 12 1/2″ scope any time any conditions. 

Keith Rivich( Cypress, Texas, USA), from an online thread entitled: Arc second seeing

While larger scopes can resolve smaller perturbations in the atmosphere, which means they virtually never see a “still” atmosphere, nonetheless, the seeing varies on a scale of days, hours, minutes, and even seconds.

When the seeing is appreciably “sub arc-second”, the larger scope will reveal the details visible with that kind of resolution, while the smaller scope will see a more stable, yet lower-resolution, image.

So in a given hour of the night, seeing will vary and the larger scope will occasionally reveal an image resolution not obtainable by the smaller scope.

And, in the event of truly spectacularly-good seeing conditions (which happens occasionally where I observe), the larger scope will simply make the smaller scopes seem like regular resolution broadcast TV versus a 4K Blu-Ray disc image.

You may not like the image in a big scope under mediocre seeing conditions, relative to the small refractor, but you will always see more if you look for longer than a few seconds.

That assumes equal optical quality, though, a condition I think may be rare.

Starman1( LA, California, USA), from an online thread entitled: Arc second seeing

But the larger scope doesn’t have to operate at its theoretical limit to exceed the resolution of a smaller scope.

It does have to have good optics, collimated and cooled, something I don’t see all that often.

Starman1( LA, California, USA), from an online thread entitled: Arc second seeing

JimP, on 27 Feb 2020 – 11:28 PM, said:

If a 12” inch telescope has the ability to resolve approximately 0.4 arc seconds does this mean anything larger than 12” inches will show a brighter image but one is not likely to have seen conditions that will allow any finer detail to be seen.

Jim

The way I see it, as Tom Polakis said above, this is a measure of width of the seeing induced in-focus diffraction pattern over time. At times seeing will be as good or better and easily diffraction limited, at other times it will be less and fall below the diffraction limit. Both over shorter intervals. During the better moments, a slightly larger aperture should be diffraction limited for short intervals at least some of the time for a “diffraction limited” scope that is not otherwise compromised by poor collimation or thermal instability. When the scope and the seeing are both diffraction limited, the view can be amazing. The diffraction limit for seeing is about Pickering 7/10 or better, which should easily be the case for a 12″ resolving to the Dawes limit. I’d think the 12″ would be relatively steady and the larger aperture less so, but the larger aperture still performing to it’s limit at least some of the time. 

This may likely be the case for a slightly larger aperture, adequately prepped and thermally stable for observing, so long as seeing effects at that larger aperture do not fall below the diffraction limit, i.e., in seeing less than about Pickering 7/10 all of the time. But, even then, a larger aperture is packing those induced seeing effects into a slightly smaller seeing induced diffraction artifact due to it’s increased resolution, so a larger aperture continues to retain most of it’s resolution advantage until, as Don says “you may not like the image in a big scope under mediocre seeing conditions”, which means and as Mitch describes, the aperture is bloating or speckling it’s star images. At that point, all bets are off. For stars at 0.4″ arc, anyway. 

For extended object resolution, I agree with Jon in that the Dawes limit (0.4″ arc in this case) is not a good indicator of lunar or planetary resolving power. Dawes applies to two relatively bright high contrast point source diffraction patterns, not extended objects. When seeing is cooperating, we can actually see higher contrast detail to some degree well below Dawes. Even in the best seeing there are even better moments. During the best moments of the best seeing conditions, I’ve seen craters, in full crater form with a bright rim and a dark pit, on Plato’s floor that subtended an angular diameter of ~ 0.70″ arc less that Dawes calculated at 0.77″ arc for a 150mm aperture. I saw it three times during the time I was observing Plato’s floor at high magnification around 0.5mm exit pupil (300x in a 6″ aperture). That crater was less than a mile in diameter (near apogee IIRC). It has nothing to do with Dawes, only of (high) object contrast “transferred” to the image on very small scales. 

Bottom line, as I understand it and somewhat by anecdotal evidence, in seeing that good there are better moments, coupled by the higher resolution of the larger aperture packing energy into smaller diffraction patterns, and that Dawes has nothing to do with extended object resolution. So, in my view, a larger aperture will still hold some or much of its resolving power until the tiny image begins to speckle and bloat in lesser seeing being affected by the aperture itself. I recall the general rule of thumb is, in theory and maybe empirically so, bloating will begin at about 3 times the aperture in diffraction limited seeing conditions. 

Asbytec(Pampanga, PI), from an online thread entitled: Arc second seeing

 

Here is a way of looking at the flaw in using Dawes or Rayleigh limits to discuss the amount of detail/contrast transfer in telescopes.

Regarding the in focus diffraction pattern of a star.  There’s a central disc of light, then a dark ‘ring’ – the first minimum – and then the first bright ring, a second minimum, a second (much fainter) maximum and so on…..

The radius, in arc seconds, to that first minimum is 138/D where D is aperture in millimetres..

To the first ring the radius is 163/D,  (telescopoptics.net)  These numbers are a few percent smaller for increasingly obstructed scopes but for this discussion we will stay with unobstructed….Also let’s assume a fairly ordinary star of around 6th magnitude where the second bright ring is too dim to see…

Imagine your 150mm scope is showing a beautiful, motionless first ring on a night of good seeing at 300x or so.

The first minimum is at a radius of 138/150 = 0.92″  and the first ring is at a radius of  163/150 = 1.09″.   These numbers differ by only 0.17″, the dark space (depends on the brightness of the star) is, at most about 0.3″ across.  Yet you can clearly see it….if seeing allows. 

This must mean that the  ‘balls of confusion’ are only about o.3″ or a bit less in size,  allowing you to see the diffraction pattern in all its glory in your 150mm scope.  At lower magnifications views will be ‘sharper’ and the views will be ‘tighter’ or more ‘refractor-like’ or whatever non-empirical descriptors you care to use…  Your 6-inch scope will perform to its resolution capability and deliver its very best contrast transfer in this scenario…  

Now crunch these same numbers for a 16-inch scope.  400mm of aperture, so, first minimum will be at 0.35″ and the first ring will be at 0.41″ which differ by only about 0.06″ now and the black space between the disc and the ring will be barely 0.1″.

On the same night assuming the same approx ‘balls of confusion’ of about 0.3″ the diffraction pattern,disc, dark space and ring will be smeared by the atmosphere into speckles or a fuzzball. No diffraction pattern for you!   The scope will not perform to its resolution capability nor achieve its best contrast transfer…

BUT….

The radius of this fuzzball in the 16-inch will be approximately 0.7″ (radius to first ring of 0.41″ plus about 0.3″ of ‘confusion’).  

The bigger scope will still out-resolve and out-contrast-transfer more detail than the 6-incher!!  Even when you cannot see the diffraction pattern of stars in the 16-incher…

Now all of the above are for a night of decent seeing where a 6-incher can clearly see its diffraction ring.

Imagine much bigger ‘balls of confusion’ such that the 6-incher cannot see its diffraction pattern.  Just a fuzz ball maybe 1.0″ or 1.5″ in size.  ‘Balls of confusion of 1.0″ or even larger….. In this situation the 16-inch  won’t out-resolve or out-contrast the 6-inch.  The bigger scope will just show more detail/speckles in the fuzzball. 

The latter scenario plagues most of us on most nights. 

The TL;DR of all the above:

On nights of mediocre/poor seeing where the diffraction pattern is completely smeared out in a 6-inch, the 16-inch will have little or no advantage in resolution or contrast transfer.  These nights are all too common.

On nights of good/excellent seeing where the diffraction pattern is clearly seen in the 6-inch the 16-inch will still out-resolve and have better contrast transfer than the 6-inch even though the diffraction pattern is not visible.  These nights are less common but, at least in my neck of the woods, happen a dozen or so nights a year….

On nights when the diffraction pattern is discernable in a 16-inch there will be glorious viewing for its owner and the 16 will truly ‘blow away’ the 6 in all categories of viewing..  These nights are exceedingly rare even in the florida Keys and are unknown where I usually observe…

Cotts(Madoc, Ontario, Canada), from an online thread entitled: Arc second seeing

 

Having tried a 6″ apo (the Explore Scientific), I can say that while they are nice, you will see more in a 10″ reflector for sure, unless there are significant optical defects or the cooling/collimationg are bad (both fixable, at least).

If an 8″ reflector is optimized, it’s going to be hard to find a 6″ refractor that will beat it on the planets. For 10″, no competition.

areyoukiddingme, from an online thread entitled, A Newtonian , SW150mm ED Refractor or SW180mm Mak?

 

If an 8″ reflector is optimized, it’s going to be hard to find a 6″ refractor that will beat it on the planets. For 10″, no competition.

True words.

At a star party I attended, two friends had their scopes set up side by side. Seeing was decent and both scopes were pointed almost straight up at Jupiter. One scope was a 6″ f/15 Jaegers achromat and the view was very nice and crisp. I saw nothing to fault the view. Nice! The other scope was an 8″ f/6 Starfinder Dob. This scope had been “tuned up” with a high spec replacement secondary, minor tweaks and the original primary. Case closed – no need to run back and forth – the view was better in the Dob. Better brightness (expected), but more detail too. Beautiful!

From my own perspective, I once owned an 8″ F/12 achromat and it gave nice planetary views. Side by side with my 10″ f/5, plate glass primary Dob – no contest – 10″ wins over the 8″.

All the scopes in these comparisons had good optics – there weren’t any dogs in the race.

You want to kill Mars? Better hurry up, it’s coming! Build yourself a 10″ Dob with great optics.

Here is one (if still available) from our own CN classifieds. Royce 10″ f6 with Moonlight focuser diagonal rings

Bargain for what’s included.

siriusandthepup(Central Texas, USA), from an online thread entitled, A Newtonian , SW150mm ED Refractor or SW180mm Mak?

A well built 10″ Newt with good optics simply cannot be beat.

SteveG(Seattle WA, USA), from an online thread entitled, A Newtonian , SW150mm ED Refractor or SW180mm Mak?

 

***

The big dob will gather a ton more light and enable you to see things that are far fainter than the refractor. You can’t cheat physics. A big dob like that is a fantastic visual deep sky telescope, you start to see structure in galaxies and such.

The refractor will show very beautiful images of brighter objects, though. It will also be very worthwhile, just in a different way.

On planets, the refractor will generally always do a good job. The dob will have the potential to exceed it, and by a lot, but you will have to work out all the issues to get it:
1. Great atmospheric seeing.
2. No tube currents, everything cooled down.
3. Perfect collimation.
4. Great optics.
5. Some kind of tracking would help.

If you get all of that thedob will win but seeing is challenging for large scopes.

Mitrovarr(Boise, Idaho, USA), from an online thread entitled, Visual Observing: big APO refractor Vs big Dobson

There would be a significant difference in brightness and resolution between 130-140mm and 12-16” (304.8-406.4mm) aperatures.

E7FVPZR, from an online thread entitled, Visual Observing: big APO refractor Vs big Dobson

I would point out that for normal middle class budgets an 8 inch apo and mount is a heart-stopping expenditure.    The only reason I brought it up is because you wanted to compare to a big dob.  Well you would need some might fine mighty precise apo aperture to keep up with a 16 inch mirror.

You have to adjust your expectations.  In your 16 inch the Perseus double cluster will be a mind blowing shockwave of stars.  In your 4 inch refractor you will get a gorgeous detailed view of the region that will dazzle.  But the clusters themselves will be redueced to one or two dozen granules.

When you observe in small apertures, things you take for granted from observing with a big scope just disappear outright, or become very difficult to spot.

Generally I like to pair a refractor with another scope.

gnowellsct, from an online thread entitled, Visual Observing: big APO refractor Vs big Dobson

Along with the stated brightness and resolution, the Dob should have a much larger exit pupil at the same mag.

Junomike(Ontario, Canada), from an online thread entitled, Visual Observing: big APO refractor Vs big Dobson

My 14 inch Dob showed colors and detail on the planets that were far better than any apo scope of 6 inches and below

that I had or used. The Dob scope would show structure in DSO’s, that the refractor could never match.

Sadly, I can no longer use a Newtonian reflector, and certainly not a Dobson type mount with my medical condition.. 

Rutilus(England), from an online thread entitled, Visual Observing: big APO refractor Vs big Dobson

 

I’ve gotten some very pretty crisp views with my 6″ f/10 newt, and still do.  My 10″ f/7 also gave very nice crisp views too.

I have a 130 APO and it is very good, with nice crisp views.  It would not compare to my 10″ f/7, and the 6″ f/10 gives the 130 a run for its money.

Garyth64(Michigan, USA), from an online thread entitled, Visual Observing: big APO refractor Vs big Dobson

mccarthymark, on 24 Sept 2020 – 7:53 PM, said:

Get the best of both worlds.  Use the 16-inch dob for deep sky, then make a 5-inch diameter (or whatever will fit) off-axis mask at the front of the UTA to use for double stars etc., or for when seeing doesn’t support the larger aperture.

It’s not the same. A 4 or 5-inch refractor will give you a wider true field. 

I played with a 6-inch off-axis mask with my wife’s 14.5-inch equatorial Newtonian on several nights when Saturn and Jupiter were well placed and tossed the mask in the trash. While the full aperture was not reaching its full potential because of seeing, it did reveal more detail and the larger aperture and more vivid colors were greatly appreciate.

Alan French(Upstate New York, USA), from an online thread entitled, Visual Observing: big APO refractor Vs big Dobson

It is hard to beat a large aperture scope for planetary and deep space views. A 14 inch+ Dob will pretty much blow just about any refractor out of the water for details, color, and yes, even contrast. If you could find a nice 10 inch apo refractor, that might be different.

Jeffmar(Utah, USA), from an online thread entitled, Visual Observing: big APO refractor Vs big Dobson

Well, I don’t have a premium 130-140mm  refractor or a 16″ dob, but I do have a couple premium 4″ refractors (FC100DL and FC100DF) and a premium 20″ dob (Obsession Classic with an Ostahowski mirror).

From my experience is that the dob gives much better views of the planets but only when the scope is precisely collimated, well cooled and the seeing is good.  The advantage of the smaller refractor is that you can just plop it down on any given night and fifteen minutes later it is ready for high magnification viewing (small doublets cool very fast), there is no need to collimate and it performs reasonably well even when the seeing isn’t good.  The 20″ Obsession is capable of showing much more planetary detail but  only after it has been properly collimated and cooled (cooling can be a challenge with a big dob) and it is much more sensitive to bad seeing (common where I am).

Ithegla Sar(Pacific NW, USA), from an online thread entitled, Visual Observing: big APO refractor Vs big Dobson

This seems to be the consensus. I’m starting to realize that one cannot replace the other.

Urbyz(Netherlands), from an online thread entitled, Visual Observing: big APO refractor Vs big Dobson

 

Yep.  IF you have to drive to dark sites, how transportable is your Big Dob?  I can rest my 5″ F5 frac on the passenger seat of my Mustang, put the VersaGo in the trunk, and loading / unloading is no sweat.  And, since it’s a Mustang, I can get to the dark site… faster…

Bomber Bob(USA), from an online thread entitled, Visual Observing: big APO refractor Vs big Dobson

I have owned six 152mm refractors, two f/8 achromats (not recommended for planetary), a Meade 152ED f/9, and an Astro Physics 6″ f/8.

None of them were nearly as competent on any class of object as my 12″ dob.  Under my light polluted skies, the 6″ refractors lacked the limiting magnitude to do very well on Globular Clusters and open clusters (Caroline’s Rose is far better in a 12″ than a 6″ anything) and had far to small of an image scale (at the same exit pupil) as the 12″. 

On Planetary Nebula, once again, to get the image scale, the image gets very dim in a 6″ anything.  Subjects like the Eskimo or the Saturn nebula are much more gratifying in a 12″.

You can see small, low surface brigntess galaxies in a 6″ Apo, but once again, if you use enough power to make them big, the larger scope has a major advantage and in most cases, galaxies will show more extension and more structure in a 12″ than in a 6″ Apo.

Planets are far better in a 12″ when seeing permits which is not a rare thing, though it is not a common thing either. I have had the best planetary results in my 35 years of observing with a 12″, and I have owned scopes up to a C14.

When you factor in the mount required to hold these big, long telescopes steady at high power, the total effort to use one can be as much as that required to run a C14 (and I owned both of these scopes at the same time, so made numerous comparisons and in the end concluded that the 6″ Apo was too much trouble for the aperture it provided.)

This being the refractor forum and everything, I don’t plan on getting into any battles that can’t be won, but my experience is that even a 10″ reflector with good mirrors is a better visual scope than a 6″ Apo.  You just see more on just about every kind of object with it….

Eddgie(USA), from an online thread entitled, Visual Observing: big APO refractor Vs big Dobson

Urbyz, on 24 Sept 2020 – 8:28 PM, said:

This seems to be the consensus. I’m starting to realize that one cannot replace the other.

That was my conclusion too after many years in the hobby.  Each telescope still has their pluses and minuses.  Of course, we each have our favorite.  Mine is a TAK128.  Easy setup and no collimation to worry about.  But when the seeing is above average  my Dob and SCT get some time too.  Enjoy the choices.

Delgado39(California, USA), from an online thread entitled, Visual Observing: big APO refractor Vs big Dobson

 

Quote

 

Anyhow the reason there aren’t that many 160 to 180 mm apos out there is because the cost curve of the telescope runs up against the income distribution of the country in which it is sold.

 

I think there are several reasons… this thread points to some of them. Refractors are bestvas small scopes and as their aperture increases, their advantages are less and their liabilities greater. Reflectors are just the opposite, their liabilities become less and less, their advantages are more important. 

Chromatic aberration scales with focal ratio divided by aperture. Double the aperture, the focal length increases by a factor of four. 

 

Jon Isaac(California, USA), from an online thread entitled, Visual Observing: big APO refractor Vs big Dobson

Yep. That’s why my largest refractor is 4″. That seems to be a sweet spot for apo refractors considering cost, cooling time, mount requirements, field of view and overall portability.

Ithegla Sar(Pacific NW, USA), from an online thread entitled, Visual Observing: big APO refractor Vs big Dobson

For planetary, the big dobs will give better views at higher power (on a good seeing night) than the refractor can. The caveat is “good seeing”, and the other points above recollimation, cooling down etc. I have made direct comparisons on Jupiter and Saturn at 200+x. The 4″ apo gives sharp and beautiful views but it can’t match the colour, contrast and resolution (and therefore greater detail) of a big dob at similar power, especially when you go over 200x. At those powers the exit pupil of the 4″ is simply too small, and you can’t beat the physics of resolution vs aperture.

In terms of travel, am not tempted to get a bigger dob because my 12″ does a great job and is highly portable. It has a home-made truss that I can set it in about 5 minutes, and it takes up about the same room in the car as a 40lt Esky. It cools down a lot quicker than the big dobs too. It also does a great job in city light-pollution: it will always pull in more detail than a smaller scope on DSO’s even in polluted skies because you can go higher power (and hence darker sky background) for the same exit pupil as the smaller refractor. (I have never understood the comments that bigger dobs are no good in the city!)

Dean D(South Australia), from an online thread entitled, Visual Observing: big APO refractor Vs big Dobson

More aperture is better for just about everything except low power wide field viewing, IMO.  For planetary observing, the atmosphere will be a major factor in what you can see.  Globular clusters will explode with many more stars visible with big aperture.  Faint galaxies will be brighter with more aperture.  Double stars will be more separated with the extra resolution that big aperture offers. 

Coopman, from an online thread entitled, Visual Observing: big APO refractor Vs big Dobson

An 8 inch dob with a good mirror is going to better 99% of the apos out there (since there are few 7 inch or larger apo) since you can get a 10, 12, 14 inch scope for reasonable money the dob is the way to go for deepsky and planets when the sky permits it.

Rich A(Toronto, Canada), from an online thread entitled, Visual Observing: big APO refractor Vs big Dobson

OP, out my 50+ years in the hobby, I was a Refractor Snob for the first 44 years.  Then I bought a used 1971 Criterion RV-6… that one Old Newt changed this hobby for me.  A good thing, because that Orion XT12g almost turned me off reflectors… what a big floppy heavy mess it was.  Yes, it pulled in more faint fuzzies, but high-power planetary on that AZ platform?  Nope.  I prefer GEMs for serious observing (30 minutes or more studying 1 object).  So, I meant it about my 1980s Meade 826 — it does everything well.  It’s easy to set up, take down, and use — easier than my much more $$$$ 2017 APM 152ED.  (In fact, I’m thinking of selling the Big ED.)  A light 8″ F6 Newt on a solid GEM with good visual tracking up to 400x… what’s not to love??

In just a few years, I went from 0 Reflectors to 5… 3 Newts + 2 Casses.  Very happy camper.  Not turning in my Refractor Fan Membership Card, but I’m enjoying this mix of lenses & mirrors.

Bomber Bob(USA),  from an online thread entitled, Visual Observing: big APO refractor Vs big Dobson

Heh, I’m actually glad my bigger dobs are seeing limited all the time.  That way I don’t feel that I’m leaving resolution or a higher power view on the table.  

I’ve owned an 8″ F/5.9 dob for over 15 years.  It’s my 2nd.  I bought one a year earlier, then sold it when I got my 12.5″ f/5 truss dob.  I paired that dob with a 6″ F/8 dob for grab ‘n’ go.  Ended up selling it.  Why?  I kept hitting the ‘scope’s limit on nights, where the 8″ would be largely limited by seeing where I lived then.  I felt every time I maxed out the 6″ that I was missing out, because the 8″ would have let me see that much more, or use higher powers.  That bothered me to no end, so that ‘scope found a new home and I bought another 8″.  The bummer was the first 8″ had identical diffraction patterns on either side of focus.  The new one doesn’t (it still goes up to 400x very nicely, thus a good mirror, but not perfect like the first).  

So I see a dob that can never hits it’s limits due to seeing a good thing.  That way I know I’m always at the limit for the current viewing conditions, and not being artificially limited by the ‘scope.  But that’s just me 

hoof(Washington, USA), from an online thread entitled, Visual Observing: big APO refractor Vs big Dobson

 

Most of my observing is from my balcony, and most of that is on the planets.

I’ve tried a 6″ Explore Scientific apo, which was fun to play with, but like others I found the trade-off of aperture vs. pain to be beyond what I wanted to deal with. Add in a big mount, counterweights,  . . . so I concluded that the sweet spot for me on a refractor was probably around 5″ at maximum.

Since then I lucked across parts to assemble an 8″ F7 Newtonian. This scope has changed my opinion on the refractor/reflector comparo on planets.

The key reason is that the primary is 20mm thick quartz, and it’s up and running in a few minutes. You just need to blow the boundary layer off and you are ready to go. It is ready to view faster than my 80mm.

So the trade-off for reflectors regarding cooling doesn’t have to be a trade off if you get the quartz substrate.And as for views, I didn’t have the refractor at the same time, but if my memory serves, it’s just no contest. I think you’d need more than 6″ of the best refractor goodness to beat it, and even then I’ll be observing for an hour before the refractor has cooled.

At least that is my experience with 8″. I’ve liked it so much that I’ve ordered a new 12.5″ primary in thin quartz. I anticipate difficulties getting it mounted without inducing astigmatism. But if it cools like the 8″, I expect to be a very happy camper.

areyoukiddingme(USA),

from an online thread entitled, Visual Observing: big APO refractor Vs big Dobson

 

A top notch bigger Newt  in the 10 to 14.5″ range will kill any 6″ APO in my super steady seeing.  A world class 6″ APO and mount are gonna be $10 to 13k when a used 14.5″ Starmaster or other top notch Dob is gonna be around $3 to 5k.

Go up to a 8″ APO when the cost is around 25 to 35k for the scope and mount and it still won’t touch a 14.5″ Zambuto in my seeing.

CHASLX200(Florida, USA), from an online thread entitled, Visual Observing: big APO refractor Vs big Dobson

 

bobhen, on 25 Sept 2020 – 11:50 AM, said:

Visual observing: big APO (130mm) refractor VS. big (12″) Dobson.

 

 

This is what Sky and Telescope had to say about the SV 130mm refractor when they reviewed that scope…

 

“A 5-inch refractor is ideal for high resolution visual use on the sun, moon, and planets. Its resolving power of 0.9 arcseconds is perfect for sampling the typical seeing of 2 to 3 arcseconds common at most amateur observing locations….”

“…and they (5-inch refractors) aren’t as susceptible to poor seeing as large scopes.”

 

OTHER CONSIDERATIONS:
If planetary imaging is in your future, consider the Dobsonian but with some type of tracking. The refractor will also do nicely but for planetary imaging aperture is better, as one can eliminate poor seeing and add contrast etc. in processing.

 

If long exposure, deep sky imaging is in your future, consider the refractor.

 

If Ha solar observing or imaging of solar prominences and disk features is in your future, consider the refractor.

 

 

And yet thousands of observers here in the NE, not known for its great seeing, have routinely seen large apertures outperform high end apos.  Myself among them.  It doesn’t matter that this was published in S&T.  They’re wrong.

I like my 5″ triplet 130mm apo.  But the fact is that two Skywatcher Dobs 10″ and 12″ licked it in a fair fight.  And my C14 licked my FS128 in a fair fight.  And the 92mm apos (both of them) are outperformed by the c8 that they ride on.  And the c8 gives the 5″ apo a run for the money on planets.

Some of the best imaging of the sun is now done with SCTs.

But anyhow we’re talking Dobs here (thank goodness, for a change) vs refractors but the point is the same.  Outlandish claims are outlandish.

gnowellsct(USA), from an online thread entitled, Visual observing: big Apo refractor vs big Dobson

bobhen, on 25 Sept 2020 – 8:11 PM, said:

HERE is a link to very detailed website about astronomical seeing. Below is a relevant statement from that site…

 

“How often do nights of excellent seeing occur? At the William Herschel Telescope site in the Canary Islands, even this superb viewing location, second best in the northern Hemisphere, has many nights of relatively poor seeing: the distribution is positively skewed… and at this excellent site, a 10 inch telescope will experience seeing limitations on 9 out of 10 nights.”

 

If a 10-inch scope is seeing limited 9 out of 10 nights at La Palma, which has some of the best seeing in the world! – What are the odds in your backyard? And if the planets are not well placed, like the past few years, and at many times during an appearance, that will also lower those odds even more.

 

As to imaging, I stated in my earlier post “imaging” is a “different animal”, as it is possible to eliminate some seeing issues and add contrast, etc. in data capture and processing.

 

Bob

 

I liked this much better, it’s realistic.

““A 5-inch refractor is ideal for high resolution visual use on the sun, moon, and planets. Its resolving power of 0.9 arcseconds is perfect for sampling the typical seeing of 2 to 3 arcseconds common at most amateur observing locations….””

The statement that a 10 inch scope will experience seeing limitations 9 nights out of 10 nights requires some explanation.

The Dawes limit for a 10 inch scope is 0.456″.  That means that is sometime during the night, the seeing is not 1/2 arc-second, a 10 inch scope will be seeing limited.  Not many places have better than 1/2 arc-second seeing but plenty of places are between 0.5″ and 1″.

The reality is that in 1″ seeing a 10 inch will significantly out perform a 5 inch.

This is why Sky and Telescope said that a refractir with a Dawes limit of 0.9 arc-seconds is well suited for typically seeing of 2-3 arc-seconds.  It’s not well suited for 1 arc-second seeing but it is well suited for rather poor seeing.

 

Jon Isaac(California, USA), from an online thread entitled,

bobhen, on 25 Sept 2020 – 8:11 PM, said:

HERE is a link to very detailed website about astronomical seeing. Below is a relevant statement from that site…

 

“How often do nights of excellent seeing occur? At the William Herschel Telescope site in the Canary Islands, even this superb viewing location, second best in the northern Hemisphere, has many nights of relatively poor seeing: the distribution is positively skewed… and at this excellent site, a 10 inch telescope will experience seeing limitations on 9 out of 10 nights.”

 

If a 10-inch scope is seeing limited 9 out of 10 nights at La Palma, which has some of the best seeing in the world! – What are the odds in your backyard? And if the planets are not well placed, like the past few years, and at many times during an appearance, that will also lower those odds even more.

 

As to imaging, I stated in my earlier post “imaging” is a “different animal”, as it is possible to eliminate some seeing issues and add contrast, etc. in data capture and processing.

 

Bob

 

I liked this much better, it’s realistic.

 

““A 5-inch refractor is ideal for high resolution visual use on the sun, moon, and planets. Its resolving power of 0.9 arcseconds is perfect for sampling the typical seeing of 2 to 3 arcseconds common at most amateur observing locations….””

The statement that a 10 inch scope will experience seeing limitations 9 nights out of 10 nights requires some explanation.

The Dawes limit for a 10 inch scope is 0.456″.  That means that is sometime during the night, the seeing is not 1/2 arc-second, a 10 inch scope will be seeing limited.  Not many places have better than 1/2 arc-second seeing but plenty of places are between 0.5″ and 1″.

The reality is that in 1″ seeing a 10 inch will significantly out perform a 5 inch.

This is why Sky and Telescope said that a refractir with a Dawes limit of 0.9 arc-seconds is well suited for typically seeing of 2-3 arc-seconds.  It’s not well suited for 1 arc-second seeing but it is well suited for rather poor seeing.

Jon Isaac(California, USA), from an online thread entitled, Visual observing: big Apo refractor vs big Dobson

 

My location is frequently 1.8 to 2.0 arcsec seeing, at least according to:

https://www.goodtostargaze.com/

Tonight’s prediction is 1.8 to 2.1 at different hours. For comparison San Diego is .6 to .8 (lucky buggers!).

These are, of course, average estimates. So even if a 10″ Dob has a Dawes limit of about .5 arcseconds, my bet is that where I live there are moments and little 20-30s runs on the seeing that would get me close to that resolution.

Given that planetary viewing is a patience game, I’m more than happy to wait for those moments.

areyoukiddingme(USA), from an online thread entitled, Visual observing: big Apo refractor vs big Dobson

 

Anyone who has spent time at an eyepiece knows that this is the way it works: You observe a while, might seem okay, suddenly it becomes spectacular, then it goes back to okay then it gets bad. Then it might stay bad for quite some time. But giving up is not how planetary observers are made. It is disingenuous to suggest that the best one can do is with a 5-in aperture even if it is an apo.

And since when is a tiny exit pupil the best way to see anything if observing over extended periods? actually I don’t know why I’m arguing this point. Anybody who spends 15 seconds on a good 10 to 15-in newt will know that it is outperforming a 5-inch Apo.

I shall add I think refractors are fantastic and they represent just in the optical tubes about 1/2 of my total investment in astronomy including mounts oculars SCTs and innumerable other peripherals.

I have invested heavily in them because they’re beautiful and deliver value to my observing as well as the possibilities of simplified set up and easier management in cold weather.

I’m not arguing against refractors I’m just saying they’re not miracle devices.

gnowellsct(USA), from an online thread entitled, Visual observing: big Apo refractor vs big Dobson

Jon Isaacs, on 26 Sept 2020 – 9:05 PM, said:

I have to think you were not hunting down faint galaxies.  And clearly you weren’t splitting double stars.

 

Jon

Even in my back yard, my small (these days) 8″ F6 Newt delivers 2x to 4x the number of galaxies in the Coma-Virgo Realm of Galaxies than my APM 152ED F8.  FWIW:  When I really want to study the dust lanes in M31, I use my antique Tinsley 6″ F20 Cass.  Or, one of the best views I get of the Dumbbell Nebula is with my 1958 Questar Standard.  IOW:  Different objects, seeing, etc. = different scopes.

 

Buy / Use enough scopes, under a variety of seeing conditions, and you figure out that variety in type & design matter.  Not every object is a nail, so there is no one perfect hammer.

Bomber Bob(USA), from an online thread entitled, Visual observing: big Apo refractor vs big Dobson

CHASLX200, on 26 Sept 2020 – 1:36 PM, said:

A top notch bigger Newt in the 10 to 14.5″ range will kill any 6″ APO in my super steady seeing.  A world class 6″ APO and mount are gonna be $10 to 13k when a used 14.5″ Starmaster or other top notch Dob is gonna be around $3 to 5k.

 

Go up to a 8″ APO when the cost is around 25 to 35k for the scope and mount and it still won’t touch a 14.5″ Zambuto in my seeing.

Similar seeing here at The Swamp — just more clouds.  A clean & collimated reflector can challenge a much more expensive APO.  Seen it myself.  Make some modest contrast & functional improvements to that reflector, and… Wow!  I’ve seen it at the Mid-Tier level — I’m not paying Big Bucks for any scope.  This is a hobby.  Folks who have invested in top-tier refractors & reflectors probably have a different opinion, and that’s okay.

Anyway, OP, I hope we haven’t gone too far off-topic from your original question.

Bomber Bob(USA), from an online thread entitled, Visual observing: big Apo refractor vs big Dobson

Urbyz, on 24 Sept 2020 – 7:06 PM, said:

Hi there,

I’ve been a proud owner of a small 6” dobson and enjoy using it very much. Being a little smaller and looking at other scopes online, naturally the mind starts to wonder what a bigger scope might reveal through the lens. I might’ve caught some aperture envy!

Looking online i started developing an interest for refractors. Not exactly sure why, but something draws me to their form factor and it might be due to the stories about crisp, contrasty views you’ll only get with a high end APO triplet refractor. Visually as wel as for AP.

I’m very aware that larger dobsons deliver the best bang for buck views and aperture possibilities. Their big aperture lends well for viewing both DSO and planets and the dob mount lends itself perfectly for easy visual observing. But when i read high-end APO triplet refractor (~6k $) product descriptions, it tells me they are capable of also showing details in faint DSO’s and sharp images of planets at very high magnification.

Now my question is: (And forget about the cost for a minute. I realize it can costs thousands on top of the scope for a big refractor) Purely visually. What will be the difference looking at planets and dso’s through a 6k, let’s say 130-140mm, APO refractor compared to a good 12-16” dobson?

I only observe visually so far, but might take up AP in the future.

Best,

Ruben

In round numbers, the  Dob you described will resolve objects more than twice as small, which is very important for planets, and gather more than four times as much light, which is very important for DS0s.
My garden variety 6”8 Dobs have have easily out performed my pedigreed, 4” class refractors for resolution and light grasp. Expect it would take at least a 115mm refractor to equal a 6” Dob, but refractors have other endearing qualities, so I have two of them.

gwlee(USA), from an online thread entitled, Visual observing: big Apo refractor vs big Dobson

aztrodog, on 27 Sept 2020 – 2:35 PM, said:

Jon – Hard to chase faint galaxies from anywhere close to South Florida on account of light pollution. However, I have “seen” more deep sky objects from the comfort of my backyard with the 7” than any other scope. Just my eyeballs were not peeking into an eyepiece. The 11” SCT does lend itself nicely to alternative viewing of deep sky viewing.
Splitting doubles I would also vastly prefer the refractor. Much easier to make out even small elongations of really right pairs under most conditions with the 7” the larger aperture scopes I had access to,

 

Chas you need to sell your Vette, get a Yugo so you can free up some cash to buy yourself a real 6” APO and keep it long enough to see what it can do.

 

My friend Sergio owns a 16” Starstructure with a Zambuto mirror and it has yet to “kill” his Tak 152. As a matter of fact, the 152 and a smaller 90mm Tak have become his most used scopes.The 11” you sold to my other compadre here in Miami some years back is wonderful, but it does not smoke any decent 6” APO much less the 7”. And yes, our skies are just as steady as yours in Tampa and better if we travel 2 hours south into the Florida Keys. Different views with different appeal given the object and observing conditions yes, but for sure killing, smoking, leaving in the dust are not something most experienced observers who have had these two side by side for extended periods of time would agree with.
As far as costs and since you like cars….should we all drive Tesla Model 3s because it smokes anything from vettes to lambos at a fraction of the cost? I think not.

 

When I go under the stars I want a Swiss Army knife of a scope, a scope with enough aperture and the best possible optics so I won’t have to questions If I am getting the best possible image. A scope I can roll out, plug into a 12vdc source, focus and enjoy…only a refractor has checked all of those boxes for me (excluding my sorry 178ED) in close to 40 years as a backyard astronomer and countless number of telescopes.

I did lemon law the new C7 Vette. Got a spark on a lark, Got tired of fast cars and the cost that go with them. Also done with scopes.  Unless a nice used 18″ Obsession or a very well made 18″ F/6 Dob pops up local for a crazy price i don’t see me having a scope again.

That 16″ Zambuto would be a easy 1000x+ killer on the planets on my best nites. The 6″ Tak runs out of light past 550x.  That Tak can do 100x per inch easy on the moon and doubles.

But planets dim out at powers above 500x in a 6″ Tak. I have the money to buy most anything i want, but just don’t want anything really at this time. I have had 6″ APO’s and a few ED’s. They can’t touch a bigger top notch made Newt 10″ and bigger. I have world class seeing that lets big Newts shine. I also had a 178ED that was a hunk of junk with the mount image shift and a lens that would never stay on center.  I could never wrap my head around spending big money on a 6″ AP or Tak when a bigger Newt just does so much better for much cheaper.

CHASLX200(Florida, USA), from an online thread entitled, Visual observing: big Apo refractor vs big Dobson

 

Quote

Splitting doubles I would also vastly prefer the refractor. Much easier to make out even small elongations of really right pairs under most conditions with the 7” the larger aperture scopes I had access to,

Something ain’t right. The Dawes limit for a 7 inch is 0.65″, the Rayleigh criterion, 0.79″.  These are both difficult because the Airy disks are overlapping. With a 10 inch, they’re wider, with my 13.1 inch, they’re wide.. of course seeing allowing.

When you say “larger scopes you had access to”, these were not scopes you owned and setup?

There’s no doubt Newtonians require careful attention and looking through someone else’s scope is rarely a good way to evaluate the capabilities of a scope, refractor or reflector.

Jon Isaac(California, USA), from an online thread entitled, Visual observing: big Apo refractor vs big Dobson

CHASLX200, on 27 Sept 2020 – 11:36 PM, said:

You do any real side by sides with my 826 you bought and that 6″ ED?  By heck that 826 Meade ran neck and neck with a 6″ APM and Skywatcher 150ED.

Yes, after I upgraded the 826 focuser to the Lumicon helical, I put it up against my APM152ED and saw for myself with each scope on a StarFinder EQ.  The ED can go 75x per inch, and the Galilean are sharper disks; and, it presents tight doubles with better clarity.  But, the 826 shows more belt colors on Jupiter & Saturn, more belt to zone intrusions, and overall both disks are brighter.  For DSOs the 826 pulls way ahead.  $300 investment vs. $3000…

Bomber Bob(USA), from an online thread entitled, Visual observing: big Apo refractor vs big Dobson

 

gnowellsct, on 28 Sept 2020 – 12:05 AM, said:

Yeah I really much prefer GEMs.  Doesn’t change the fact that two Skywatcher dobs (10″ and 12″) beat the pants off my 5″ apo one year.  Even with the tappa tappa tappa to keep Jupiter in the field of view, it was a blow out.  Skywatcher 2, Astro-physics zero on that particular object on that particular night.

 

But the 130mm is a scope I really like and I wouldn’t trade it for a 12″ SW dob.

 

Greg N

 

The few times I’ve had my 12.5″ Starmaster and AP 130 GT out at the same time, the Starmaster has always won on planets.  The AP 130 GT sure isn’t going anywhere though.

turtle86(Florida, USA), from an online thread entitled, Visual observing: big Apo refractor vs big Dobson

Urbyz, on 24 Sept 2020 – 7:06 PM, said:

Hi there,

I’ve been a proud owner of a small 6” dobson and enjoy using it very much. Being a little smaller and looking at other scopes online, naturally the mind starts to wonder what a bigger scope might reveal through the lens. I might’ve caught some aperture envy!

Looking online i started developing an interest for refractors. Not exactly sure why, but something draws me to their form factor and it might be due to the stories about crisp, contrasty views you’ll only get with a high end APO triplet refractor. Visually as wel as for AP.

I’m very aware that larger dobsons deliver the best bang for buck views and aperture possibilities. Their big aperture lends well for viewing both DSO and planets and the dob mount lends itself perfectly for easy visual observing. But when i read high-end APO triplet refractor (~6k $) product descriptions, it tells me they are capable of also showing details in faint DSO’s and sharp images of planets at very high magnification.

Now my question is: (And forget about the cost for a minute. I realize it can costs thousands on top of the scope for a big refractor) Purely visually. What will be the difference looking at planets and dso’s through a 6k, let’s say 130-140mm, APO refractor compared to a good 12-16” dobson?

I only observe visually so far, but might take up AP in the future.

Best,

Ruben

Straight answer: you cannot beat aperture. The difference is so big that the differences will be overwhelmingly obvious. Even mediocre dobs of that size will be perfect APOs in that range.

On planets: you will see detail within the detail you can see with the APOs.

DSOs: objects will become structured. As you go up in size, “faint fuzzies” are no longer that fuzzy nor faint.

Simeos Pedro, from an online thread entitled, Visual observing: big Apo refractor vs big Dobson

 

Your 45lbs. C14 is easier to hold and lift onto a lower mount and pier saddle than a 8″ f/7 APO would be. Tube dimensions matter. The 60lbs. 8″ APO would require a taller pier/mount because of its longer tube.  Lifting 60lbs. shoulder height or higher is tough and dangerous for one person to do. I had a 45lbs. AP 175EDF a few years ago and mounted on a 52″ ATS portable pier with a AP1100 mount with a saddle height of 68″. I chose that height of ATS pier to keep the eyepiece height high enough for observing overhead objects and still be seated comfortably at the eyepiece.  I don’t like lying on the ground to observe.  I’m 6’3′ tall and believe me, lifting that 45lbs 175 to my shoulder height into the rings 68″ up was a task in strength and mental fortitude.  I would have to focus totally on the task before and after. I was nervous mounting and dismounting it.  All my larger aperture Dob’s (14″-24″) were a piece of cake to set up and pack up compared to the 175 and it’s other heavy accessories.  My 16″ f/4.5 Zambuto Dob outperformed the 175 anyway so the 175 got sold.  I’ve come to realize that I a lot more comfortable observing at the eyepiece position that a Dob offers versus what a refractor does. The Dob’s eyepiece location makes more sense to my body mechanics, that is to stand up, or sit on my CatsPerch observing chair, and to and look level headed into the eyepiece rather than looking down.  With a refractor, you’re looking down — bad for your neck, head, and eyes.  Eye floaters appear in your view looking downward more often than when looking level.  At a 45° and higher telescope angle, the Dob’s horizontal eyepiece works better for your neck, head, and eyes than looking downward at the end of a refractor for longer periods of time.

 

gnowellsct, on 28 Sept 2020 – 4:58 PM, said:

Well I think the 8 inch APO is unwieldy and I would be hard pressed to put one into my Accord.  But on the other side of this argument I regularly transport 150 lbs of mount, counterweights, and pier.  Mount: two sections of 15 lbs each, counterweights, 18 lbs each, counterweight shaft, 20 lbs, ATS pier (looks big but all aluminum) 30 lbs, OTA C14 45 lbs, battery 50 lbs (that’s the worst part of my rig), apo 12 lbs, eyepiece box 30 lbs, observing and two folding chairs, 30 lbs = 30+54+20+ 30+45+50+12+30+30 = ~300 lbs, though I suspect I overestimated a few items and would peg it at 250 lbs.

 

It’s my favorite set up but not when the observing window is short or the forecast is iffy.  It is definitely my wife’s favorite setup.   It is so nice to have a spouse who likes astronomy I try to cater to her preferences.

 

The reason the APO is a problem is that it would likely take up two seats, as I found out when I transported a 10″ f/6 Newt.  I had to put the front passenger seat down and slide the tube in from the rear passenger door.  That would leave no room for wife and dog.   The stupid Accord designers decided to save ten bucks by not making the rear seat split 60/40, either the whole thing goes down or it stays up.  But even if it was 60/40 there still would be a problem of a lost seat and lost trunk space, causing some items from trunk to have to move into the rear seat and now room for wife but no dog.

 

But with a C14 it all works out for wife and dog and a rig worthy of the Normandy invasion.  And with great performance capabilities.  

 

Greg N

 

C14+CFF at Chimney mountain 6-20.jpg

 

Peter Natscher(California,USA), from an online thread entitled, Visual observing: big Apo refractor vs big Dobson

 

The Newts beats the APO in every way if it has Zambuto like optics. The Newt is 30 times cheaper and 5 times lighter. Once you go 7″ or more for a APO you are talking 20k and up and big money for a mount. I would much rather have a 8″ F/8 Newt over a 8″ APO even for free. Since setting up a APO that big would be a 6 to 7 trips scope to set up.  While i can leave a old EQ mount outside and just throw the Newt OTA on the mount and be viewing in 3 mins time.

CHASLX200(Florida, USA), from an online thread entitled, Visual observing: big Apo refractor vs big Dobson

 

To be continued………………………

 

 

Neil English unearths plenty more historical evidence testifying to the prowess of Newtonian reflectors in his large historical work, Chronicling the Golden Age of Astronomy,  published by Springer-Nature.

 

De Fideli.