‘Plotina’; the author’s ultraportable 130mm f/5 Newtonian reflector.
In this department of astronomy, the names of Herschel, South, Struve, Dawes, Dembowski, Burnham, and others are honourably associated and it is notable that refracting-telescopes have accomplished nearly the whole of the work. But reflectors are little less capable, though their powers seem to have been rarely employed in this field. Mr. Tarrant has lately secured a large number of accurate measures with a 10-inch reflector by Calver, and if care is taken to secure correct adjustment of the mirrors, there is no reason why this form of instrument should not be nearly as effective as its rival.
W. F. Denning, from Telescopic Work for Starlight Evenings (1891), pp 290-291
Eye seeth afore I measureth.
Introduction: Having spent several years enjoying the views of double stars of varying degrees of difficulty with a variety of classical achromatic and apochromatic refractors of various apertures (60mm-150mm), this author has dedicated the last 15 months investigating the prowess of Newtonian reflectors in regard to their efficacy in splitting double stars. Surprisingly, a 8″ f/6 Newtonian with traditional spider vanes and a 22 per cent central obstruction was found to be noticeably superior to a first rate 5″ f/12 glass, as well as a 180mm f/15 Maksutov Cassegrain, on all targets, including double stars.
These experiences have collectively led to a deep seated scepticism concerning the traditional claims of self appointed ‘authorities’ who have tended to downplay the Newtonian reflector as a worthy double star instrument. But as the quote from Mr. Denning’s book states above, this prejudice is not derived from sustained field experience. Instead, it is cultivated by, at best, tenuous theoretical considerations. And yet theory counts for nothing if contradictions are found by experimentation, and must be revised in light of new evidences brought to the fore by active observers.
In this capacity, this author has spent several months investigating the performance of a very modest 5.1 inch (130mm) f/5 Newtonian reflector on an undriven alt-azimuth mount. The instrument was modified in two principal ways:
- The original secondary mirror was replaced with a slightly smaller flat (blackened around its periphery), giving a central obstruction of 26.9 per cent, significantly lower than Schmidt and many Maksutov Cassegrains of similar aperture.
- Both the primary and secondary mirrors were re-coated with ultra-high reflectivity (97 per cent) coatings delivering a light throughput broadly equivalent to a refractor of similar size.
The instrument has a single stalk supporting the secondary mirror which produces greatly reduced diffraction effects compared with more traditional Newtonians, yet was found to be sufficiently rigid to deliver very sharp and detailed views of the Moon, planets and deep sky objects.
The single stalk, rigidly supporting the secondary of the 130mm f/5 Newtonian.
The optical train can be accurately aligned in minutes by means of fully adjustable screws on both the primary and secondary mirrors and an inexpensive laser collimator.
The collimating screws behind the primary mirror.
Preliminary field testing has shown that the telescope provides very fine high power views of stellar targets under fair to good conditions. Even at powers beyond 50 per inch of aperture, stars remain round, free of astigmatism and perfectly achromatic. Furthermore, the diffraction spikes attributed to Newtonians are much subdued in this instrument owing to its single vane secondary support. The diagram below shows the relative intensity of diffraction spikes manifesting from various secondary mounting configurations and the reader will note the minimal effects of a single support (seen on far left).
Comparison of diffraction spikes for various strut arrangements of a reflecting telescope – the inner circle represents the secondary mirror.
Materials & Methods: The telescope was mounted on an ergonomic but sturdy Vixen Porta II alt-azimuth mount equipped with slow motion controls on both axes. the instrument was carefully collimated prior to the commencement of observations using a laser collimator. No cooling fans were employed. A red dot finder was used to aim the instrument and various oculars and barlows were used to resolve pairs. For fainter stellar targets, the system was centred first using a 32mm SkyWatcher Plossl which delivers 20x and an expansive 2.5 degree true field.
Time: 00:00-00:30 UT
Seeing: Antoniadi II-III
Epsilon Lyrae: x 271; all four components cleanly resolved, stars round, white and undistorted. No diffraction effects noted.
Pi Bootis: Easy at 150x. Components appearing white and blue-white.
Mu Bootis (Alkalurops): Wonderful triple system; fainter pair (magnitudes 7 and 7.6) separated by 2.2″ and perfectly presented at 271x. This pair has an orbital period of just 260 years!
Epsilon Bootis: Primary (magnitude 2.5) presenting in a lovely ochre hue and its fainter companion (magnitude 4.7) easily picked off at 271x.
Delta Cygni: Magnitudes: 2.89, 6.27, separation: 2.7″
Well split at 271x, although conditions a little turbulent and not yet at an optimal altitude for observation.
Time: 00:00-00:30 UT
Seeing: II. Indifferent seeing at sunset (III-IV), improving as the night advanced (II).
Xi UMa: beautiful clean split of this 1.6″ pair (magnitudes 4.3 and 4.8) at 271x
Epsilon Bootis: textbook perfect split @ 271x
Delta Cygni: Child’s play this evening, separation 2.7″. Companion presented as a perfectly round, steely grey orb @271x.
Beta Lyrae: remarkable multiple star system. Four white/blue white stars framed in the same field at 271x.
O^1 Cygni: a corker at 20x, but more fetching at 81x. Orange and turquoise stars, with the former showing its blue magnitude 7 companion.
Time: 22:30 UT
Seeing: II-III, clear, brightening moon, twilit
Iota Cassiopeiae: Just one entry tonight. More challenging to locate owing to its relatively low altitude above the northern horizon and the encroach of twilight. All thee components well resolved at 271x. This is the third successful split of this attractive multiple star system with the same instrument.
Time: 22:10 UT
Seeing: II, partially cloudy, twilit.
Epsilon Bootis: Another lovely split this evening @271x. Primary(magnitude +2.5) orange and the secondary a regal blue (magnitude 4.9) separated by 2.8″.
Xi Bootis: Striking yellow and orange components (magnitudes 4.7 and 7, respectively), separated by ~6.5″ and beautifully framed @ 150X.
Rho Herculis: A comely pair of blue-white stars shining at magnitudes +4.5 and +5.4. Easily resolved (4.0″)@271X.
Epsilon 1 & 2 Lyrae: textbook perfect split of all four components @271x. Subtle colour differences noted between the stars.
Delta Cygni: Perfectly resolved at 271x. Magnitudes: 2.89, 6.27, separation: 2.7″
Seeing: II, very good, mostly clear, twilit, bright Moon low in south.
Marfik(Lambda Ophiuchi): Quite hard to track down owing to an unusual amount of glare in the southern sky. System split at 271x. The components ( magnitudes 4.2 & 5.2), well resolved. Tightest system so far resolved with this instrument: 1.4″. Both stars appeared creamy white and orientated roughly northeast to southwest. Superficially, very much like Xi UMa but slightly more challenging.
No’ bad ken.
Time: 00:10 UT
Seeing: I-II, excellent steady atmosphere, no cloud, twilit, cool.
Pi Aquilae: Another good target affirmatively resolved this evening. Separation 1.5″ with magnitudes of 6.3 and 6.8. Power of 271x applied. First hint of duplicity seen shortly after local midnight when the system was quite low down in the east, but much better presented at 23:45 UT when it rose a little higher.
Delta Cygni: Another textbook perfect split! This system is child’s play with this telescope, but remains a good indicator of local seeing.
I would warmly encourage others using this telescope, or its closed tubed counterpart, to confirm these findings.
Time: 22:45 UT
Seeing: II, good stable air for double star work, cloudless sky, twilit.
Epsilon 1 & 2 Lyrae: beautiful easy and dazzling split of all four components @271x
Delta Cygni: Another textbook perfect split of this very unequal magnitude pair @271x
Mu Cygni: difficult to find as it is currently lower down in the east under twilit conditions. Excellent multiple star system, A-B well split @271x, colours white and yellow (+4.8/6.2 magnitudes, respectively), separation ~1.66″. Another tight, unequal magnitude pairing. C component too faint to pick off in the twilight. D component (+6.9) seen about 3′ off to the northeast.
Doing well so far don’t you think?
Ps. Interesting findings from a few guys here.
Time: 23:10 UT
Seeing: II, almost a carbon copy of last night. Twilit.
Just two targets this evening.
Epsilon Bootis: a good ‘warm up’ system. The telescope showed a textbook perfect split during the finest moments at 271X. I have found that wearing a good heat-insulating jacket and hat gives noticeably better results on cooler nights, as thermal energy from the body can sometimes distort the image at least for a wee while.
From there I moved to my target system for the evening.
Sigma 1932 AaB: a very challenging system in Corona Borealis. It is located about 3.67 degrees directly west of Alphecca (alpha CrB) which is easily seen even in twilight. My 32mm SkyWatcher Plossl, which yields a field of view of 2.5 angular degrees was used, together with my star atlas, to finally track down this magnitude 7 system. After a few false starts, I eventually centred the target system, cranked up the power to 271x and, with a concentrated gaze, obtained a good split! This binary system consists of a pair of yellowish stars with equal magnitudes (7.3 and 7.4, respectively) oriented roughly east to west and separated by 1.6″.
Battle o’ the weans. In the foreground a 90mm Apo, in the backgroud, a 130mm Newtonian.
Time: 23:00-23:30 UT
Seeing: A fine and mild night, remaining very good (II), high pressure bubble stabilised over Scotland, some intermittent cloud, twilit. Midge flies back.
Tonight, I wanted to compare and contrast two very different telescopes in respect to their ability to split a few of the tougher pairs visited thus far; a 90mm f/5.5 doublet Apo (retail price now £912 UK) and the 130mm f/5 Newtonian (~£200 UK with the modifications).
90mm glass; difficult split @208x
130mm speculum: much more cleanly resolved@271x
System: Pi Aquilae*
90mm glass: very dim, touching @208x
130mm speculum: cleanly resolved/brighter @271x
90mm glass: dim, elongated @208x
130mm speculum: fully resolved /brighter @271x
You cannae change the laws o’ physics captain!
And ignorance of the law is no excuse.
Oh vanity of vanities!
Self-evidently, an unfair comparison: the 130mm f/5 Newtonian is clearly the superior double star instrument.
The words of the prophet, Isaiah, come to mind;
For fools speak folly,
their hearts are bent on evil:
They practice ungodliness
and spread error concerning the Lord;
the hungry they leave empty
and from the thirsty they withhold water.
Scoundrels use wicked methods, they make up evil schemes
to destroy the poor with lies,
even when the plea of the needy is just.
But the noble make noble plans,
and by noble deeds they stand.
Time: 23:05 UT
Seeing: III; significantly more turbulent than last night. Twilit.
This evening I had intended to concentrate my observations on one target; the very difficult sub-arc second companion to Lambda Cygni, using my best instrument; a 8-inch f/6 Newtonian, in order that I might train my eyes to see this companion (separated by 0.9″) in my smaller 130mm instrument.
Using the 130mm as a seeing gauge; I found Epsilon 1 & 2 Lyrae to be resolved well but nearby Delta Cygni was poorly resolved. This was also found to be the case in the 8-inch aperture.
Project shelved for a better night.
Time: 23:30 UT
No opportunities afforded this evening owing to the encroach of haar after sunset.
Let us consider some of the optical principles relevant to splitting such a tight pair.
Diffraction theory states that the position of the first bright ring (between 1st and 2nd minima) is located at a linear radius of 1.63 lambda x F where lambda (wavelength) is quoted in microns and F is the focal ratio of the scope. By dividing this quantity by the focal length we obtain the angular radius of the 1st minimum (in radians) and this yields (1.63 x lambda)/D where D is the aperture of the scope in metres.
Now, there are 57.3 angular degrees in a radian and 3600 arc seconds in each angular degree, so if we multiply the above expression by 57.3 x 3600 = 206280 and so we arrive at 206280 x (1.63 x lambda)/D.
Setting D = 0.1m for example, and lambda = 0.55 microns (green) yields 1849300 micro arc seconds, which is 1.85”.
Or more generally, the locus of the first diffraction ring is 185/D where D is the aperture of the telescope expressed in mm.
Applying this formula to the 200mm and 130 mm reflectors, the position of the first diffraction ring is 0.9” and 1.4”, respectively. Thus, the companion to Lambda Cygni will be located on the first diffraction ring in the 8-inch instrument, and inside the ring in the case of the 130mm telescope.
The primary has a magnitude of +4.5 and the secondary, + 6.3, so there is a magnitude differential of 1.8. The significant brightness differential makes this system more difficult to crack.
The Dawes limit for a 130mm (5.1 inches) ‘scope is given by 4.57/D in inches, which is ~0.9”.
More on this here.
Time: 23:30 UT
Seeing: III-IV, very turbulent
Conditions clear but remaining very turbulent. A light, northeasterly air flow is likely the culprit(see my local weather; Stirling, Scotland).
My notes show that I have glimpsed the companion to the primary on a few occasions over the last few summers with my 5″ f/12 achromatic. But I have seen it much more clearly – and also on a few occasions – with the 8″ f/6 Newtonian.
In order to maximise my chances with Lambda Cygni, I have decided to wait until August at the earliest, when the system will be high overhead here, in a dark sky. Patience is a virtue is it not? And I can afford to be patient with this one, as it is a very slow moving binary and so will remain very challenging for a good few years to come. So no hurry.
The capabilities of the 130mm f/5 on double stars have already well exceeded my expectations. My experiences with the smaller, 90mm refractor especially, have reinforced the notion that aperture is a vital commodity when it comes to seeing objects clearly and distinctly. It pays to remember that resolution scales with aperture. That’s why it is easier to see things in the 130mm than the 90mm, irrespective of how fancy its optics and mechanics are. And this can be tested, again and again and again…..ad nauseam.
This is factual knowledge, and facts are stubborn and immutable things!
Physics cares little for hubris.
Over the next few months I would like to return to the many beautiful and easy systems within reach of this remarkable telescope; even in heavy twilight.
Time: 23:00-59 UT
Seeing: II, good, a little hazy, twilit.
I walked through the garden in the cool of the evening, after a very warm and sunny day. I set up the 130mm f/5 as usual and began to explore some of the nicer double stars of the sky.
Mizar & Alcor: A perennial favourite, high overhead this time of year, dazzlingly bright, the light from these stars fills the field and induces instant joy. Well framed at 81x in my trusty Baader mark III zoom.
Cor Caroli (Alpha CVn): Easy to find under the handle of the Ploughshare. Both components appearing white to the eye with magnitudes 2.9 & 5.6.
Alpha Herculis (Rasalgethi): A corker! At 108x, this pair presents as marmalade orange and blue-green, which orbit their common centre of gravity every 3600 years.
Albireo (Beta Cygni): A stunning sight in the little reflector at 81x. Glorious contrast of colour; orange (magnitude 3.1) primary, blue-green secondary (5.1).
61 Cygni: historically very significant as the first star system to have its distance measured in 1838 by F.W.Bessel. Only 10.4 light years away. Both stars are cool, orange dwarfs with magnitudes 5.2 and 6.1.
Eta Cassiopeiae: A bit more challenging to locate in the strongest twilight coming from low in the northeast. Easily split at 81x, presenting as orange and red (magnitudes 3.5 & 7.5, respectively). These constitute a true binary system, with a period of about 480 years.
A quick peek at a more difficult pair:
Pi Aquilae: Once again, beautiful and easy to resolve in the 5.1” reflector at 243x. I have been observing this system for five years now, with various instruments. My notes from the end of July 2011 showed that it was very difficult with a high-quality 4” f/15 classical refractor, the twilight making it challenging. Observations made with variety of 5” refractors over the same period – and also in summer twilight – show that it is not difficult in these sized instruments (only anomaly recorded in an optically so-so 6” f/8 speculum used for outreach also from 2011, where it was relatively poorly seen). In the absence of a good 4” refractor at present, this provides good evidence that the 130mm reflector is indeed operating closer to the performance of a 5” glass than a 4” glass, which is very encouraging.
Before leaving the field, I spotted Saturn below the tree line in the south, so I decided to uplift the telescope on its Porta II mount and walk about a hundred yards to a grassy spot at the local primary school grounds, where I could better aim the telescope. Despite its very low altitude, it was a beautiful sight at ~150x, it glorious ring system now wide open for business. Cassini Division seen, as well as some banding on the Saturnian globe.
Vicious midge flies making any further observations uncomfortable, the vigil was aborted shortly before 1 AM local time.
Time: 23:00-30 UT
Seeing: II, good and stable, variable amounts of thin cloud, twilit.
Polaris: Always a lovely system to study, even in the twilight. In the telescope at 108x, the 2nd magnitude primary (Polaris A) presents as a beautiful creamy white, the secondary a haunting bluish grey some 6 magnitudes fainter seen in the 10 o’ clock position in the 130mm Newtonian. A third companion lies much closer to Polaris A but is woefully beyond the powers of any backyard telescope to resolve. Interestingly, all three stars in this system, located about 430 light years away, are of the F spectral class, and thus should present with the same colours. This is readily seen with Polaris A but the exceeding faintness of the Polaris B hides its true colour. Polaris B orbits A at a distance of about 2400 further out than the Earth-Sun distance, taking over 400 centuries to complete a single lap. Polaris A is a giant, pulsating star, part of a class known as Cepheids. With such stars, humans have been able to extend the plumbline of their reach into the realm of the galaxies. Stars like Polaris A have helped us gain a truer sense of the vastness of the Universe in which we miraculously inhabit. These are some of the things I like to ponder on, whilst spying the Pole Star.
16 Cygni: A fourth magnitude system a little to the northeast of the lovely red variable star R Cygni. In the 130mm f/5 at 81x, the decent light gathering power of the instrument presents the pair in their natural colours: a yellow primary (magnitude 4) and golden secondary (magnitude 6), separated by about 40 arc seconds of sky.
Eta Lyrae: Located a few telescopic fields east of Vega, this is normally a very easy system to crack at low powers (~40x) with a magnitude 4.4 blue-white primary and 9th magnitude secondary wide away. In the twilight, I find a higher power of 108x is needed to see the faint secondary well, and is even better presented again at 150x. Much more gloriously presented from a truly dark sky.
Time: 22:30-59 UT
Seeing: II-III, clear, twilit, bright waxing gibbous Moon culminating in the south. Evening made especially pleasant by the absence of midge flies, which don’t like temperatures below 10C.
After over a week long hiatus in the weather, which brought endless cloud and some rain, the sky finally cleared up this evening, allowing me to resume my adventures with my 130mm f/5 Newtonian.
Two reasonably challenging doubles to start with:
Epsilon Bootis: beautifully sharp and well resolved at 195x
Delta Cygni: Ditto @195x; always a joy to observe this system so well.
Iota Bootis: A wonderful low power system, located about 4 degrees northeast of Alkaid (at the tip of the handle of the Ploughshare). At 81x, the system was beautifully framed and showed a yellowish primary(magnitude +4.8) well separated from a bluish secondary, some three magnitudes fainter (+7.5). Very fetching colour contrast in the Newtonian!
95 Herculis: Found by panning some 10 degrees east of Delta Herculis. To my eyes, this nearly equal magnitude pairing(4.9/5.2) has a very subtle colour contrast: one appears silvery, the other creamy white. Easily resolved at 81x. Consulting my old Burnham’s Celestial Handbook Vol 2, there is an interesting discussion on the historical colour presentation of this pair, especially from some eccentric 19th century observers!
What colours do you see?
How wonderful it is to get outside on this beautiful mid-summer evening!
Time: 22:30 UT
Seeing: II, some hazy cloud, bright Moon in south.
Epsilon 1 & 2 Lyrae: Textbook perfect split of all four components at 243x
Delta 1 & 2 Lyrae: Easily found in the low power (20x) field of my 32mm SkyWatcher Plossl, just a few degrees to the east of Vega. No need for higher power with this system; lovely colour contrast – red and blue-white. Stars physically unrelated i.e an optical double.
SHJ 282: Seen in the same lower power field of Beta Lyrae, some 1 degree to its northeast. Under darker skies, it forms a wonderful sight in the 2.5 degree field of the 32mm Plossl, together with the celebrated Ring Nebula (M57). At 41x, this comely system (actually triple) looks like a copy of Albireo; an aureal primary well separated from its pale blue secondary.
Seeing: II, very good, partially clear, beautiful noctilucent clouds in the northeast, fresh westerly breeze, nae midgees.
The weather has been quite unsettled of late, with little in the way of clear skies, but this evening I grabbed an opportunity with both hands and fielded my bonnie 130mm Newtonian.
A number of systems visited this evening including:
Delta Cygni: wonderful split and (as usual) easily resolved at 243x. Lovely round stars well separated in the twilight.
Epsilon 1 & 2 Lyrae: Textbook perfect at 243x
Epsilon Bootis: Very easy for this telescope, as I have found on many occasions now. Lovely colour contrast at 243x
Pi Aquilae: Better positioned these days. Easily split at 243x
11 Aquilae: Found by centering Zeta Aquilae in the low power (20x) field. 6th magnitude 11 Aq lies just one degree or so to its west. At powers up to 100x or so, only the white 6th magnitude primary is visible, but when the power is cranked up beyond about 150x, the much fainter 9th magnitude companion was observed wide away. Reasonable concentration is required to tease this out of the twilight. Once picked off, the greyish companion was better seen at higher powers (243x). This system is far more glorious in a fully dark sky, and I shall look forward to visiting it again in August.
All in all, a grand half hour under a Scottish summer sky. My little Newtonian reflector is most assuredly a proficient double star telescope. The unbridled joy of discovery!
Time: 22:45-23:20 UT
Seeing: Excellent, I-II, gentle breeze, very little cloud, twilit.
After assessing the seeing in the 130mm Newtonian and judging it fine ( as evidenced by cleanly splitting Delta Cygni at 243x), I fielded my 8-inch f/6 Newtonian and turned it on Lambda Cygni, now considerably higher in the sky and applied a power of 450x. I also employed a Baader single polarising filter, which helped to reduce glare and darken the sky. I could indeed see the companion to the primary star intermittently and oriented north to south. And during the better moments I could see that it was clearly disembodied from the primary. I then turned the 130mm on the same system, employing a power of 365x with the polarising filter. Letting the image settle down as it moved across the field, I observed good elongation in the same orientation, but no separation.
This was a most exciting and encouraging vigil, the first of many more I hope.
Seeing: II, good clear spells, some cloud, westerly gusts, cold, twilit.
After a day of heavy and frequent rain showers, I enjoyed a short clear spell around midnight.
Iota Cassiopeiae: Fairly tricky to track down in twilight, but was rewarded with a lovely clean split of this picturesque triple star system at 243x.
Eta Cassiopeiae: Picturesque colour contrast pair (A/B orange and yellow). Easy to split at powers at ~100x.
Sigma Cassiopeiaie: located a few degrees southwest of the easternmost star in the constellation ( Beta), this is a wonderful target for small telescopes. It consists of two blue-white stars separated by about 3.2″. The primary shines with magnitude 5.0 and the secondary, 7.2. Best seen at magnifications > 150x.
Delta Cephei: Beautiful and easy with the 130mm Newtonian. The stars appeared pure white and easily resolved even at low power but nicely framed at 81x. The primary is actually another Cepheid variable (described above in relation to Polaris).
Two tighter test systems visited:
Delta Cygni: good clean split at 243x
Epsilon Bootis: ditto at 243x
Seeing: III-IV, below average seeing, partially cloudy.
Fairly choppy seeing this evening, as evidenced by somewhat bloated stellar seeing disks observed with the 130mm f/5 Newtonian.
Delta Cygni: barely resolved at 243x
Epsilon Bootis: split but not cleanly at 180x
Xi Bootis: yellow and orange pairing, easily resolved (6.4″) at 150x
Pi Bootis: Blue and yellow components, easily resolved (5.6″) at 150x
Zeta Coronae Borealis: Lovely yellow and blue-green components easily resolved (6″) at 150x
Mu Bootis (Alkalurops): All three components resolved easily with the 130mm Newtonian at 243x. System previously visited on May 12 last. The two seventh magnitude stars (B/C) were surprisingly well split (~2″), a consequence I suppose of their low brightness which curtails the size of their seeing disks. Fainter pairs seem less susceptible to seeing conditions.
Time: 22:40-23:00 UT
Seeing: III-IV, remaining turbulent, mostly cloudy.
Further trials with the 130mm f/5 Newtonian.
Delta Cygni : unresolved at 183x
Epsilon 1&2 Lyrae: resolved at 183x
Cor Caroli: very pretty at 63x
Time: 22:45- 23:00 UT
Seeing: III-IV, very turbulent mostly cloudy, a few suckerholes appearing here and there.
Two instruments fielded this evening; a 130mm f/5 Newtonian and a 90mm f/5.5 apochromatic refractor (price now hiked up to £1017?! i.e. fourth successive hike since review)
Epsilon Bootis (Izar): Companion resolved reasonably well with 130mm reflector but very poorly (if at all) with 90mm refractor at comparable magnifications i.e.~180x. Quite revealing really!
Mission aborted owing to light drizzle.
Time: 22:30-23:00 UT
Seeing: III, partially clear, cool, twilit.
The conditions were slightly improved over last night. I fielded the 130mm f/5 Newtonian again and examined the following systems. I employed a single polarising filter which does a very good job removing some glare and improving the aesthetic of the stellar images, especially in twilight.
Epsilon 1&2 Lyrae: easily split at 181x.
Epsilon Bootis: well split at 180x
Delta Cygni: good split at 180x and 243x
Low down in the east, I visited Delphinus for the first time this season.
Gamma Delphini: A corker at 181x! Located some 100 light years from the Solar System, the primary(magnitude +4.4) shines with a lovely marmalade orange hue, while the secondary (magnitude 5.0) shows up as lime-like. 9 arc seconds separates them.
Struve 2725: Seen in the same high power field as Gamma Delphini, this fainter system can be seen a little to the southwest of Gamma. This pair is a bit more challenging to spot, the primary and secondary having magnitudes of 7.5 and 8.4 respectively and orientated north to south. To my eye they both look white and are separated by 6″.
No’ bad innings for an average July evening, ken.
Time: 22:30-23:00 UT
Seeing: II-III, an improving picture, though not where I would like it to be. Partially cloudy, twilit.
Systems visited this evening with the 130mm f/5 Newtonian (with single polarising filter) included:
Delta Cygni: well split at 181x
Iota Cassiopeiae: A beautiful, delicate triple system, well resolved at 181x but more compelling to behold at 243x
After spending about five minutes admiring the comely, sanguine Garnet Star (Mu Cephei), I move the instrument a little to its southwest until I arrived at a field of view containing two other stellar systems of interest:
Struve 2816: A magnificent triple system (actually quadruple). All three stars are arranged in a line running roughly northwest to southeast. A/B looks yellow to the eye (magnitude +5.6) with two equally bright stars (C and D), located 12″ and ~20″ away from the primary, respectively. A grand sight at 181x.
Struve: 2819: Just off to the northwest of Struve 2816, this is a fainter system requiring high powers to see well. Both stars appear white to the eye. The primary is magnitude + 7.4 and has a fainter companion (magnitude +8.5) ~13″ off to its northeast. Best seen at 243x.
Very much looking forward to darker and more stable skies coming back in a few more weeks.
Time: 22:20-30 UT
Seeing: sultry, clouded out, midge flies by the legion, twilit.
Lens versus Speculum.
I was hoping to get some observing done this evening, as the forecast looked reasonably promising after a long spell of very unseasonal weather (The Open at Troon sure wasn’t pretty lol). I have not been able to make any additional progress beyond what I’ve recorded but having been at this a few months now and having seen what I’ve seen, my conclusions are as follows;
The modified 130mm f/5 appears to be an excellent double star instrument! This came as a quite a surprise to me, as I was not entirely prepared for what it could deliver given its very modest cost. All of this can be tested, of course, and I’d warmly encourage you to have a go.
The instrument will comfortably outperform any 90-100mm refractor given a fair trial (proper acclimation, optical train alignment, reasonable to good seeing conditions, etc.). It is especially adept at resolving close, fainter pairs of roughly equal brightness.
Millimetre for millimetre, its performance in comparison to a refractor of equal aperture is much closer than is commonly reported (or commonly believed), though I would concede that the refractor will have an edge when pushed to the limits*.
*Valid only over the aperture ranges studied.
My conclusions are fully in agreement with the comments made by W.F. Denning (1891), reproduced above.
I will continue to monitor these and other double stars, God willing, in the coming months and years and will report back in due course.
It has been an absolute pleasure discovering the many charms of this little Newtonian. As telescopes go, there is something very endearing about their ingenious simplicity, and given half a chance, they can show you remarkable things.
As I write this, there are more encouraging signs that the prejudice traditionally attributed to Newtonians for this kind of work is being lifted and that is great to see! Just have a look at the CN Double Star forum to see some examples. I believe much of this prejudice is/has been due to the usual suspects: laziness, lack of interest, somewhat irrational, material attachment to other kinds of telescopes, and the like. You see, you don’t need a big vainglorious refractor (I should know, I’ve got one lol) to do this kind of work, and dare I say, one can actually derive a greater level of satisfaction achieving goals with these modest instruments over more traditional ones. You begin to see the hobby in a whole new light.
Thank you for following this blog.
Date: August 17, 2016
Time: 00:05h BST
Seeing: Excellent: I, excellent definition, fairly bright sky owing to very late gibbous Moon low in the south, gentle westerly breeze.
Instruments: 203mm f/6 & 130mm f/5 Newtonians, Baader single polariser.
Observation: The 8-inch reflector easily resolved Lambda Cygni B (0.9″), clearly seen at 450x and orientated at right angles to the direction of drift (E-W). Both components presenting as perfectly round and clean white. Deeply impressive!
The 130mm f/5 showed the system as plainly and strongly elongated N-S, power employed x325. Careful attention to accurate collimation necessary. Best evidence for the appearance of duplicity thus far recorded with this instrument.
Date: August 28 2016
Time: 23:10 BST
Seeing: Excellent (I), a bonnie evening, very steady, no clouds, no Moon, cool.
Instruments: 203mm f/6 and 130mm f/5 Newtonian reflectors, Baader single polariser.
After obtaining an excellent high power split of delta Cygni & pi Aquilae with both instruments, I turned the telescopes toward lambda Cygni. The 8-inch served up another clear split of the 0.9″ B component at 450 diameters, just like the evening of August 17. The 130mm, once again showed strong elongation (north to south orientation) at 325x and 406x, but was not split.