A Newtonian Travel ‘Scope

Wednesday, February 3 2016: SkyWatcher has established a solid international reputation for producing high quality Newtonian optics for the modern amateur astronomer, and at prices that won’t break the bank. Having been thoroughly satisfied with a 8″ f/6 Skyliner Dob, I became very curious about a smaller, model – the Heritage 130P (a 5.1″ f/5 Newtonian with a parabolic primary) tabletop Dobsonian – which promises to provide decent light grasp and resolution in an ultra-portable package for take anywhere travel and short grab ‘n’ go excursions to the back garden.

The telescope was purchased new from Rother Valley Optics on Tuesday morning, February 2, and arrived in the mid-afternoon today. The price, inclusive of postage, was £129.

The telescope came double-boxed and involved no assembly. The optics looked clean and streak-free. A neat instruction manual accompanied the instrument.

The Heritage 130P Dobsonian as received.

The Heritage 130P Dobsonian as received.

 

 

 

 

 

 

 

 

 

 

The ‘scope, weighing about 6 kilos with the mount, has a built-in carrying handle for swift transport into and out of the house.

Following along the same lines as their extremely successful flextube line of larger Dobs, the Heritage 130P can be extended to reveal the upper tube assembly, lengthening the tube from just 38cm to about 61cm. The lower assembly is adorned with the names of time-honoured astronomers, celebrating four centuries of telescopic astronomy. While some folk might find this ‘tacky,’ I rather liked it.

The Heritage 130P fully extended.

The Heritage 130P fully extended.

 

 

 

 

 

 

 

 

 

Remarkably, the telescope was almost perfectly collimated out of the box, as evidenced by the just slightly offset red dot from the centre-marked spot on the primary mirror. That’s a nice touch, as one can imagine the reaction of a complete novice were he/she to discover that the optics were delivering iffy views as a result of mis-aligned optical components. It might be enough to put someone off the hobby for good.

Note the position of the red dot from the laser collimator; just a shade out of whack.

Note the position of the red dot from the laser collimator; just a shade out of whack.

Once the collimation was tweaked, I investigated retracting and extending the tube assembly several times to investigate the rigidity of the structure. I am pleased to report that the collimation held quite well but might still require last-minute tweaking for more demanding tasks, such as obtaining the best lunar and planetary views, as well as double star work. Overall though, this is a very well thought out piece of kit and certainly better than I had anticipated.

 

 

 

 

The telescope primary and secondary mirrors are fully adjustable and can be aligned in a matter of minutes. Unlike the three ultra-thin spider vanes on larger models, the secondary mirror on the Heritage 130P is affixed to a single vane, which is a good bit thicker than the latter; a necessary design compromise to maintain that little bit more stability to the optical train.

The adjustment screws behind the f/5 parabolic primary mirror.

The adjustment screws behind the f/5 parabolic primary mirror.

The secondary support is of high quality and is easily adjustable with a user supplied hex wrench.

The secondary support is of high quality and is easily adjustable with a user supplied hex wrench.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The focuser is unusual. Unlike standard rack and pinion or Crayford type focusing mechanisms, the Heritage 130P employs a simple helical focuser which involves rotating the eyepiece either clockwise or ant-clockwise to bring objects to a sharp focus. In addition, the length of the upper tube can also be adjusted to accommodate cameras and other equipment. In short, any eyepiece will reach focus using a combination of these procedures. Only 1.25″ oculars can be used with the instrument, however.

The unusual helical focuser on the Heritage 130P Dobsonian.

The unusual helical focuser on the Heritage 130P Dobsonian.

 

 

 

 

 

 

 

 

 

 

Some observers may find reaching precise focus a little fiddly, but with a bit of practice, it works smoothly and accurately.

The Heritage 130P also came with a simple red dot finder (RDF) to aid in locating objects quickly under a dark sky.

The basic but useable red dot finder is easily attached to the upper tube assembly with a small screw driver.

The basic but useable red dot finder is easily affixed to the upper tube assembly with a small screw driver.

A particularly attractive feature of the instrument as received is the dovetail mounting of the optical tube assembly which enables one to remove the tube assembly from the mount proper for even easier storage.

The optical tube can be removed from the mount if necessary to aid storage/transportation.

The optical tube can be removed from the mount if necessary to aid storage/transportation.

In addition, the dovetail plate allows the user to mount the instrument separately on other types of mounts such as this author’s ergonomical Vixen Porta II alt-azimuth for an alternative style of observing. What a nice touch!

The SkyWatcher Heritage 130P mounted on the author's Vixen Porta II alt-azimuth mount; a particularly stable configuration.

The SkyWatcher Heritage 130P mounted on the author’s Vixen Porta II alt-azimuth mount; a particularly stable configuration.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Optical testing: Although the instrument suffers from the introduction of considerable amounts of stray light during daylight use without employing some sort of light shroud, I set the instrument up in the late afternoon, aiming the instrument at a roof top about 100 yards distant. I didn’t wait around to use the supplied oculars (which are adequate but not great for testing) but instead decided to push the ‘scope as hard as I could. To that end, I ran inside and affixed a good quality 6mm orthoscopic to a 2.25x Baader shorty Barlow lens, which would deliver a power of 244 diameters. Inserting these into the helical focuser, I carefully rotated it until best focus was achieved. Although the view was a bit drowned out with extraneous light, I am happy to report that the image of the terracotta roof tiles came into very sharp focus; a great initial sign that the optics were of potentially high quality.

After dark, more cloud encroached, but I waited for the odd sucker hole and was rewarded by a clear spot corresponding to Auriga, then high in the eastern sky. Relocating the instrument in a dark spot in the garden, I centred the bright star, Capella, using my multi-coated 32mm SkyWatcher Plossl in the field (yielding a true field of 2.5 degrees!) and was delighted to observe (with my eye glasses on)  a beautifully sharp vista, with pinpoint stars across most of the field. Then, I investigated the high power view of Capella at 244x and after refocusing, was thrilled to see a tight white Airy disk with diffraction rings a shade more prominent than what I have observed in my work horse telescope, a larger 8″ f/6 Dobsonian. This could be explained by the larger central obstruction of the Heritage telescope (~29 per cent by aperture) as compared with 22 per cent for the larger 8 inch.

On a whim, I moved the instrument north-eastward from Capella and centred the star, theta Aurigae. Focusing as accurately as I could, I was able to steadily hold its very faint companion at 244x, some 4 arc seconds away from the primary. Very encouraging to say the least!

It wasn’t long before the skies completely clouded over, and the drizzle came back, ending my first light vigil under the stars. Needless to say, the instrument performed surprisingly well under admittedly dodgy observing conditions.

More testing in the pipeline though.

Thursday, February 4, 2016

11:00am

Having collimated the telescope in situ and placed a makeshift light shround around the upper telescope assembly (UTA), I am happy to reaffirm that the telescope delivers tack sharp images of distant willow tree branches at 244x.

Friday, February 5, 2016

The Heritage 130P has a parabolic primary mirror, that is, it is figured into the shape of a parabola. Why is a parabolic shape responsible for such sharp images in a Newtonian reflector? It’s an interesting question, yet many amateurs accept it as a given. But we can do considerably better than that. We can analyse the properties of the parabola, one of the conic sections beloved to the mathematicians of classical antiquity, and thereby gain a deeper appreciation of why this shape, over all others, is chosen by opticians in the fashioning of high quality primary mirrors. Our analysis will borrow from the approach of the great French mathematician, Rene Descartes (1596-1650), who developed a way of investigating geometry using algebra.

A parabola is the set of all points which are equidistant from a given point called the focus and a given line known as the directrix.

The image below outlines the basic features of a parabola drawn on a x-y axis.

The Parabola

The Parabola

 

 

 

 

 

 

 

 

 

Let the focus be the point S( a,0) and the directrix be the line x=-a, as shown in the diagram. Consider any point on the parabola, P(x,y).

Thus, by definition, the length of SP = length of PM

So [(x-a)^2 + y^2]^0.5 = x + a

Therefore, (x-a)^2 + y^2 = (x+a)^2

Thus, x^2 -2ax +a^2 + y^2 = x^2 + 2ax + a^2

From which y^2 = 4ax ( Eq 1)

This is the standard form of the equation of a parabola.

Consider next the parametric equations x = at^2 and y = 2at.

Substituting the expression for x into equation 1 we obtain;

y^2 = 4a^2t^2 = 4a(at^2) = 4ax

So, x = at^2 and y = 2at represents the parametric coordinates of any point on the parabola y^2 = 4ax.

We can use this to derive two more equations that will enable us to arrive at the result we want. Consider the diagram drawn below.

The parabola with the point P defined parametrically.

The parabola with the point P defined parametrically.

 

 

 

 

 

 

 

 

y^2 = 4ax

Differentiating implicitly with respect to x we obtain;

2yf'(x) =4a

so f'(x) = 2a/y, which is the gradient of the tangent at any point.

Now since y = 2at, the gradient becomes 2a/2at = 1/t

And so the equation of the tangent to the parabola at the point P is given by:

y – 2at = 1/t(x-at^2)

Multiplying across by t  gives;

ty – 2at^2 = x-at^2

or  x – ty + at^2 =0 ( Eq 2)

Also, the gradient of the normal at P = -t and so the equation of the normal will be:

y – 2at = -t(x-at^2)

or tx + y – 2at – at^3 = 0 ( Eq 3)

Now we are ready to obtain further information from the parabola under discussion.

Let the tangent at P intersect the x-axis at R and the y-axis at U, and let the normal to the parabola at P intersect the x-axis at V, as shown in the diagram below:

parabola 3

The coordinates of R are obtained by setting y = 0 in equation 2

x – ty + at^2 =0 and so if y = 0 then x = -at^2 and so the coordinates of R are (-at^2, 0)

The coordinates of U are obtained from setting x = 0  into equation 2, from which it is easily shown that y = at i.e. U(0, at).

The x-coordinate of V can be obtained by setting y = 0 in equation 3;

tx + y – 2at – at^3 = 0 and when y = 0 we obtain:

t(x- 2a – at^2) =0,and since t cannot equal zero we have

x = 2a + at^2 and so the coordinates of V are given by (2a + at, 0).

From these results it is possible to verify the following:

(i)  U is the midpoint of PR

(ii)  length of SR = length of SV = length of SP

(iii) US is parallel with PV and that PU is perpendicular with SU

I will leave these as exercises for the interested reader.

Now, to the meat of the analysis. Consider a line PZ drawn parallel to the axis of the parabola as shown in the diagram below:

parabola 4

 

 

Since  length SP = length SV so too must angle SPV = angle SVP

But angle SVP = angle VPZ since PZ is parallel with RV

So angle SPV = angle VPZ

But ZPV is the angle of incidence of a ray of light incident upon a reflective parabolic surface and so the law of reflection requires that the angle of reflection be the same i.e. angle VPS.

But since P is independent of S, the result implies that any ray of light parallel to the axis will be reflected through the focus, S.

This is the reason why parabolic mirrors work so well, as they completely avoid a phenomenon known as spherical aberration, which can can plague other kinds of optical designs.

That’s enough math for one evening eh.

After a day of more or less constant rain, the sky appears to be clearing up and so I’ll get some more time under the starry heavens using my little parabolic Newtonian.

Thank goodness for small mercies!

Saturday, February 6 2016

Time: 00:05h

The telescope was collimated perfectly before use and left to cool in a dry, unheated shed. Initially, I had intended to use my Baader zoom and dedicated 2.25x Barlow to observe Jupiter, now 31 degrees above the horizon. To my chagrin, I discovered that this combination failed to reach focus. Due to the constant interruptions from clouds and with the rain never far away, I did not want to retract the UTA enough to get it to focus. Instead I chose a 7.5mm Parks Gold ocular and 2.25x Barlow yielding 195x.

Though the helical focuser is a bit fiddly and takes some getting used to, I am happy to report that the Jupiter images were wonderful in this telescope, with lots of nice detail showing up under moderate scrutiny. The planet’s enormous equatorial belts were seen in their faithful colours and many shades of tan were observed. A Baader Neodymium filter took away a little bit of glare surrounding the planet, helping to bring out more subtle details. Although I felt 195x was a little too high, and would have been happier with 160x, I was most impressed by what this inexpensive Newtonian was delivering.

Jupiter as seen through the Skywatcher Heritage 130P Dobsonian at midnight of February 6.

Jupiter as seen through the Skywatcher Heritage 130P Dobsonian at midnight of February 6.

Turning then to some brighter stars appearing from behind the clouds, I was equally impressed by how well the instrument focused them down to tight round Airy disks at the highest powers pressed into service (244x). The telescope seems quite immune to atmospheric turbulence as judged by the calmness of the images. Returning to a 32mm Plossl, I enjoyed a spell binding few minutes drinking up the famous Double Cluster (Caldwell 14) in Perseus. The 20x delivered by this eyepiece provided a very generous field of view, allowing both star clusters to be easily framed in a most beautiful portal.

This is certainly not a toy telescope! It is impressively powerful with high quality optics. Indeed my initial impressions were very similar to this assessment made by Ralph Bell back in 2009.

Monday, February 8 2016

Time: 18:30-45 UT

I enjoyed another brief vigil under the stars with the Heritage 130P Newtonian.  Charging the telescope with a 32mm Plossl (20x), I first visited the Pleiades, now high in the southern sky. Its constituent stellar components focused to fine points of light, pure white as the driven snow, with excellent contrast. Though I did not do a side by side comparison with my 80mm f/5 shorttube refractor, I was immediately aware of the Heritage’s significant advantages in light gathering power, with many more fainter members coming through at a glance. Then, I moved the instrument southwards, where majestic Orion was just about to culminate. The view of M42, the Great Nebula, was a sight for sore eyes. Cranking up the magnification to 81x with my Baader Zoom, I enjoyed a sumptuous field of view dominated by the emission nebula and Trapezium stars at its heart. The hinterland of the nebula was jewel encrusted with brilliant white stars set against a jet black sky.

Before packing up, I examined three higher resolution targets; first Rigel, just a few degrees to the southwest of M42. Using a power of 108 diameters, I was delighted to see the faint companion to this brilliant giant star cleanly and steadily. Then I swung the telescope over to Cassiopeia, now high in the northwestern sky. First I centred eta Cassiopieae and keeping the power at 108x I was able to easily split this pair, consisting of a beautiful yellow primary of magnitude +3.5 and its ochre companion some 13 arc seconds away, shining considerably more faintly at magnitude 7.4. Finally, I moved the Heritage 130P over to iota Cassiopeiae and could make out two of the three components of this system at a glance at 108x. The third member remained somewhat more elusive though, so I attached the Baader 2.25x Barlow yielding a higher magnification of 244x, refocused, and was overjoyed to see all three components clearly and precisely!

The Heritage 130P enjoying a dry afternoon.

The Heritage 130P enjoying a dry afternoon.

The imminent arrival of another student meant that I had to end the short vigil there, but it was very rewarding nonetheless. The telescope has great potential as a deep sky instrument and appears to be no slouch on moderately difficult double stars.

Tuesday, February 9 2016

Time: 19:00-30 UT

After a cool but crisp day, I continued my Newtonian education by fielding two telescopes; the Heritage 130P and a high quality 90mm f/5.5 ED doublet on loan for a a magazine review. Both instruments were given plenty of time to thermally acclimate and placed in the darkest spot in my garden to minimise stray light flooding into the open tubed reflector.

The multicoated objective of the f/5 ED90 'scope.

The multi-coated objective of the f/5.5 ED90 refractor.

The sky after sunset was clear but the stars were corruscating fairly wildly. Transparency was excellent though, so I decided to assess the seeing conditions some more by turning the 130P on Castor, now quite high in the eastern sky. Charging the telescope with a power of 195x, both the A and B components were resolved but there was quite a bit of turbulence which made the stars bloat significantly from their calmer appearances under better seeing conditions.  Comparing the same target in the ED90 charged with a power of 188x, both components were also resolved but there was still noticeable turbulence. It was not quite as unsettled in the refractor though, a consequence I suppose of its smaller aperture. This demonstrated to me that poor seeing can (though thankfully rarely at my location) adversely affect small telescopes. I judged the image in the refractor to be slightly more aesthetically pleasing under these conditions.

The reader will also note that the refractor comes equipped with a state-of-the-art 11:1 dual speed micro-focuser and so was considerably easier to focus finely than with the comparatively crude helical focuser on the Heritage 130P. This may also have contributed to my conclusions regarding Castor A & B. Accurately focusing f/5-ish instruments is never a walk in the park.

Turning to M42 once again, I compared and contrasted the images in both telescopes matching their image scales as best I could (~100x). Both telescopes delivered good images but the superior light gathering power of the reflector gave it a distinct edge. More nebulosity was seen and the stellar images were noticeably brighter in the reflector. This was despite the fact that the refractor had superior contrast, with a blacker sky background.

I am hoping that conditions will improve by the time Jupiter rises in the sky in a few hours from now.

22:45 UT

The sky has completely clouded out and the forecast predicts that it won’t clear again until the wee small hours. I am very tired though, so will leave further testing for another night.

Thursday, February 11 2016

Time: 00:50h

I fielded the same two instruments tonight as last night; the 130P reflector and the ED90 refractor. I finally found a good eyepiece to optimise the 130P’s capabilities on Jupiter; a 4mm Plossl delivering a power of 165x.The ED90 was charged with a power of 150 diameters.

Seeing was only marginally improved over last night (Antoniadi III-IV) but it was nonetheless a good test of what both instruments could deliver on Jupiter under these sub-par conditions (we have a north westerly air flow here which almost invariably brings more turbulent conditions but with excellent transparency).

I fitted a Baader Neodymium filter (with very high light transmission and virtually no colour shift, more a moon and skyglow filter than anything else)  to the 130P to reduce the glare a little.

Comparing the images in both telescopes over a period of about half an hour, I gathered my thoughts.

Both showed some nice details in the equatorial belts. The ED90 image revealed hints of more subtle details at higher and lower latitudes but in the end I felt the 130P showed that little bit more. In particular, it was easier to see those details at temperate latitudes, as well as the more delicate polar shadings. One very striking difference was the colour of the Jovian disk presented in the telescopes. The ED90 was noticeably yellower in overall hue – a consequence of its imperfect achromaticity in comparison to the perfectly achromatic reflector. The latter presented a brighter disk in its true colour; much more creamy white than yellow. The Neodymium filter showed that the colour in the ED90 remained the same but with a little more light loss.

In retrospect, this should not have come as a surprise; while the refractor has a low dispersion element, which improves colour correction, it still can’t deliver perfectly achromatic images. Yes, it’s a sizeable improvement over the traditional achromat but still not perfect. Only a reflector image – which brings all wavelengths of light to the same focus – could really reveal this. In addition, a brighter image can also help the eye see finer details. You need light to see such details.

That being said, I do know the ED90 is capable of showing more on better evenings ( data not communicated) but so must the 130P, as they were both compared under the same conditions. I am eager to conduct further tests in this capacity as soon as the seeing conditions return to normal.

This was an instructive vigil. The 130P should  give very decent images of Jove when the seeing is fair to good.

15:50UT

SkyWatcher has also brought to market a related telescope called the 130PD-S, which, as far as I can tell, features the exact same optics as those possessed by the Heritage 130P but retails for about £30 more. The optics are housed in a closed tube and the spider vanes are akin to what is seen on a traditional Newtonian. It also features a low profile 2-inch dual speed focuser for precise focusing and the secure mating of a CCD camera to the instrument. The 130P-DS has proven a huge hit with astro-imagers who have used it to good effect to capture stunning views of the night sky. Featured on this link is a plethora of deep sky objects captured by this modest telescope, but the reader will also take note of the lunar and planetary images captured by the same instrument.

Although not a visual assessment, I hope you will agree that the unlying camera shows just how good the optics are in these telescopes.

Friday, February 12 2016

Time 00:01UT

The seeing was vastly improved tonight, frosty but no wind. I only had time for one target; Jupiter. Like last night I fielded the same telescopes and employed the same magnifications etc.

Both telescopes served up some excellent images, but this time there was a clear winner – the 130P.

Though the image flitted somewhat between perfect focus and slightly out of focus in both telescopes, both instruments revealed excellent details in the equatorial and temperate belts. Details in the more prominent NEB were more finely resolved in the Newtonian than in the ED90. But what clinched it for me was the sighting of the Great Red Spot (GRS) near the western limb of the planet (at 00:01UT) that was picked off in the 130P but was not seen clearly in the ED90.

As always, I would be very grateful if someone could repeat these observations if you have the 130P and a good 90mm refractor.

The 130P is turning out to be a fabulous little telescope and I am overjoyed to have made its acquaintance!

19:30 UT

I have noticed that the price of the ED90 has been bumped up by £48 in the short time since I acquired it for review. It now retails for £868?! I don’t know why this was done (it was £820 just last week, remember?), but I can tell you I do not consider these telescopes good value for money and do not understand some people’s obsession with them. Under good conditions the Heritage 130P will outperform it and for 1/6th of the price. And if the classical achromat is the prince of telescopes, Newtonians are the ruling monarchs.

I would like to keep this telescope and learn how best to maximise its potential. I have bestowed a name on her; Plotina.

After another beautiful, crisp day, the firmament was glorious after sunset, with a gorgeous crescent Moon adorning the western sky. I set up Plotina at the side of the house and trained her on our life-sustaining satellite. She cools super quick, faster perhaps than the ED refractor that now sits in its case. The view of Luna at 20x was simply breathtaking, with razor sharp crater fields and the most wonderful earthshine from its dark side. Cranking up the power to 165x, the image remained razor sharp with excellent contrast and without a trace of chromatic aberration.
After that, I headed over to eta Orionis, a fairly tricky double star and was rewarded by a good clean split of the A and B components, the primary shining about a magnitude brighter than the secondary (3.8 and 4.8, respectively) and separated by a mere 1.7 arc seconds. Because of its f/5 relative aperture, it is very important to examine such high resolution targets at the centre of the field. This can be achieved by placing the system at the eastern edge of the field and letting it drift into the centre. The procedure is repeated several times until one is certain that the duplicity has been unveiled.

Some haar moved in a short time ago but hopefully it will clear later. I hope to field my most powerful telescope, Octavius, to continue my study of the Giant Planet.

Saturday, February 13 2016

13:00UT

My luck ran night overnight, as instead of clear skies, we got a fall of snow.

The final step in keeping anything in my family is to get my wife’s approval. For that, I had to get all my facts together to make a convincing case lol:

The optical tube assembly weighs just 3.2 kilos

The little lazy Susan weighs 2.8 kilos

The telescope can be collapsed to half its length.

The tube assembly can be used with a variety of other mounts.

The telescope is easy to tweak; involving a couple of minutes with a laser collimator.

The telescope is easy to carry about using one hand, so even when I’m feeling lazy it will not overtax me.

The telescope cools rapidly, so no waiting around or extensive pre-planning involved. Just set it out 15 or 20 minutes before use and you’re cooking with gas.

Because the tube is open, the optics can be accessed to remove dust and other grime easily.

The telescope gathers a very decent amount of light to go that little deeper than my short-tube refractor; very good for deep sky viewing.

The telescope takes high magnification well; images remain sharp and well defined up 244x (higher powers not yet tested) when conditions are average to good, so will perform well on lunar, planetary and double star targets.

The telescope can be improved in a number of ways; for example, the mirrors could be re-coated to give both higher reflectivity and increased durability, the secondary size re-assessed, ways could be found to refine the helical focuser, a permanent light shroud can be installed  etc. Any amount of tomfoolery is permissible!

The instrument exudes charm and is popular with the kids.

The entire package cost only £129.

I think these points will be enough to win her over. Fingers crossed eh!

16:00 UT

Improving the Focuser:

As mentioned earlier, the focuser on the Heritage 130P is of the simple, helical variety. One simply twists it one way or another to attain a good focus. But in the field at night, it can be a little frustrating to focus precisely, especially when using high magnifications. Manhandling the focuser almost always causes the telescope to move a little, necessitating re-centering of the object under study.

Fortunately, I was able to find a very simple solution; about six inches of string!

A new improved focuser!

A new improved focuser!

 

The string is tied in a single knot around the focuser, gripping the top thread, and leaving two overhanging ends which can be pulled in either direction causing the focuser to move inward or outward, as desired. This enables both course and fine focusing with much less vibration or annoying image shift. I tested it out during the day on a variety of targets at various distances from about 40 yards to infinity and it worked really well! This will allow more quality time observing and more precise focusing from moment to moment.

I’m well happy with the improvement!

Sunday, February 14 2016

10:50UT

St. Valentine’s Day and the first Sunday of Lent.

Last night I fielded Plotina just before midnight. After snowing for much of the day, the late evening sky cleared up to reveal the hosts of the second heaven. Seeing was very good but bitterly cold(-4C), but I was rewarded by quite an extraordinary view of Jupiter and its magnificent satellite system. I watched the planet for about 40 minutes, beginning at 23:50UT and ending at about 00:35UT.

This instrument continues to humble me in many ways. The optics are unreasonably excellent in this telescope; something I was not really prepared for, but hand on heart, it has thus far given me the finest views of Jupiter in any small telescope that has passed through these parts. I made a quick sketch depicting the planet’s appearance at 23:50UT (CM II 217 degrees), when it was 33 degrees above the horizon. The Great Red Spot (GRS) was plainly seen in the eastern hemisphere of the planet. The magnification employed was 165x and a Baader Neodymium filter threaded to the 4mm Plossl.

Jupiter as it appeared though the Heritage 130P shortly before midnight on February 13, 2016. North is at the bottom and west is to the left.

Jupiter as it appeared though the Heritage 130P shortly before midnight on February 13, 2016. North is at the bottom and west is to the left.

 

 

 

 

 

 

 

 

 

Indeed, I was able to use this telescope to establish the most accurate longitude of the GRS during this apparition. The GRS was observed transiting the centre of the planet at 00:32 UT where the system II longitude was 243 degrees. Not bad eh?

In the immortal words of Alexander Pope;

Nature and nature’s laws lay hid in night;
God said “Let Newton be” and all was light.

Monday, February 15 2016

19:00UT

I subjected the 130P to a high magnification test on the first quarter Moon, at an ambient temperature of -1C. I am very happy to confirm that it handled 244x without flinching, with the craters, mountain ranges, maria and valleys  remaining tack sharp and colour free throughout. This is about as high as one would like to go with this telescope in the vast majority of applications and a testament to the quality of the underlying optics.

I would warmly encourage other individuals to test each and every one of the claims I have made about this telescope. Test everything; hold fast to that which is good.

Sound Biblical advice that!

23:15 UT

Way hay! I found me an online thread about the same telescope;  Enter the One Sky Newtonian from Astronomy Without Borders .

200K+ hits ……..Crikey!

Seems like I don’t need to say anymore, eh.

Watcha think?

Tuesday, February 16 2016

00:20UT

What a thread! The things they say about this telescope warms my heart.

That thread has saved me months of blogging; Laudate Dominum!

Gary Seronik of S&T also found the telescope a joy to use; see here.

And yet another independent review can be read here.

Here my story ends.

Thank you for viewing.

Post Scriptum: 

Thursday, February 18, 2016

10:25UT

Having just acquired the latest issue(March 2016) of Astronomy Now (pp 63), I read with interest that the current longitude (system II) of the GRS is 238 degrees. That’s just 5 degrees shy of my best estimate made with the 130P shortly after midnight on Sunday February 14 (see above). I’m thrilled to bits to have gotten so close with this nifty little travel Newtonian.

Monday March 14, 2016

I have found that the Televue bandmate planetary filter is a great match for the 130P whilst studying Jupiter.This filter will be used in all future observations of the planet with this telescope.

The Televue Bandmate Planetary Filter.

The Televue Bandmate Planetary Filter.

The primary and secondary mirrors of the Heritage 130P have been despatched to Orion Optics UK. Both mirrors will be re-coated with Hilux enhanced aluminium reflectivity coatings and a slightly smaller secondary (35mm @27% linear obstruction) is to replace the original flat.

Will report back on progress.

Tuesday, March 22 2016

The mirrors arrived back from Orion Optics UK this afternoon and I immediately set to work putting it all back together again.

Out came the matt black paint to darken the periphery of the new secondary mirror to further reduce stray light and increase contrast.

The primary mirror has been rocaoted with 97 per cent reflectivity Hilux coating. The smaller secondary ( also Hilux coated) is seen in the middle beside the original secondary.

The primary mirror has been re-coated with 97 per cent reflectivity Hilux. The smaller secondary ( also Hilux coated) is seen in the middle beside the original secondary.

 

 

 

 

 

 

 

Applying a coat of matt black paint tot he periphery of the new mirrors cuts down on unnecessary stray light entering the optical train.

Applying a coat of matt black paint to the periphery of the new secondary mirror cuts down on unnecessary stray light entering the optical train.

 

 

 

 

 

 

 

 

 

 

Side view of the recoated 130mm primary mirror.

Side view of the recoated 130mm primary mirror.

 

 

 

 

 

 

 

 

 

 

 

 

 

The primary mirror had to be re-spotted at its centre but this can easily be done by placing the mirror shiny side down on a sheet of paper and tracing round its circumference. Next, the 130mm diameter circle was carefully cut out and folded first in half, and then once again into quarters. When the paper is unfolded the centre is marked by the intersection of the two crease lines. A scalpel (lol!)was used to excise a very small hole at the centre of the unfolded paper and then it was placed over the mirror, being secured in position with some cellotape. Finally, a doughnut shaped sticker was placed on the spot exposed by the hole. Job done!

Marking the centre of the mirror for collimation purposes.

Marking the centre of the mirror for collimation purposes.

 

 

 

 

 

 

 

 

The optics were then rehoused in the tube, collimated using an inexpensive laser collimator (SkyWatcher) and briefly tested with an eyepiece. Everything looked dandy!The telescope should now deliver brighter, more contrasty images on all celestial targets. And those special coatings will last at least a quarter of a century!

Surely now Plotina will be as durable as any high quality refractor nay?

All I have to do is wait for a decent clear spell to see how well she performs under the starry heaven.

Plotina pining for a clear sky.

Plotina pining for a clear sky.

 

 

 

 

 

 

 

 

 

Wednesday, March 23, 2016

Jupiter as it appeared in the modified Heritage 130P travel Newtonian on the evening of March 23, 2016.

Jupiter as it appeared in the modified Heritage 130P travel Newtonian on the evening of March 23, 2016.

Beginning about 20:30 UT this evening, I took advantage of a clear spell after a few hours of light rain. Jupiter was about 34 degrees above the horizon and rising, and I continued observations through to 21:15 UT before more cloud rolled in. I captured some beautiful detail on the Jovian disk, including the appearance of the GRS at the planet’s eastern limb. As the minutes passed, the view of Jupiter got ever better as it gained in altitude. The 130mm f/5 performed flawlessly. The planet was brighter, crisper and cleaner than I had ever seen it before with this instrument under these conditions (Ant II). To say that I’m pleased with the modifications would be an understatement, but we’ll leave it at that.

I heartily recommend this telescope to my amateur friends across the world.

Wishing you all a very blessed Easter.

March 31, 2016

23:50 UT

I enjoyed a half hour with the Heritage 130P this evening after I had observed Jupiter. After spending some time in Leo hunting down some spring galaxies, I started looking at some double stars. Gamma Leonis was easy, Castor A and B just as easy, iota Cassiopeiae triple lovely and all three components resolved. Mizar & Alcor were glorious at 150x as was Polaris A & B. Izar (epsilon Bootis), a summer favourite, was high enough in the east for me to split it. These were all seen at 183x save for Mizar & Alcor. I then decided to try a pair of stars I haven’t visited in a while; Alula Borealis and Alula Australis in Ursa Major. They are high overhead this time of year. Aiming is quite difficult using just the RDF but with my 32 mm Plossl delivering 20x, I was able to frame them both in the same field. Starting with the orange star Alula Borealis, I employed 183x using my most comfortable ocular; the Mark III Baader Hyperion zoom set to 8mm with its 2.25x Barlow. Although this does not show the highest contrast views (but only by a surprisingly small margin!!), I was able to see the very faint spark of its companion. The primary is magnitude 3.5 but the secondary shines at magnitude +10.1 and only 7.4″ separating them! I was chuffed to see this in such a humble little reflector. Then came the icing on the cake; I moved south to Alula Australis (Xi UMa) and could see that the star looked ‘entangled’ but I knew I needed a little more power to get a clearer view. So I ran in and fetched by 6mm orthoscopic and coupled it to the little 2.25x Barlow yielding 244x, centred and focused carefully: Voila! The pair (1.6″ split) were beautifully resolved (magnitudes 4.3 and 4.8), the components round as buttons, with a kind of diffraction halo encircling them; kind of like an ‘aura’ encasing two luminous eggs in a wafer thin handkerchief lol.

I was absolutely beside myself in admiration for what this little telescope can do! I believe Newtonians have been terribly maligned as unsuitable for high resolution work relating to double stars but I now know that this is another myth. The telescope takes very high power well under reasonable seeing conditions and totally exceeded my expectations.  I feel privileged to finally ‘know’ and  to share this personal discovery with my peers.

If no one bothers, how can one ever discover the truth? The Heritage 130P is unreasonably excellent on everything; a great little bundle of joy!

April 7, 2016

Mr. Adam Blake from Pennsylvannia USA, was kind enough to share some video footage of Jupiter he captured with his One Sky Newtonian, as seen on the evening of April 5, 2016 during a spell of good seeing. He used an inexpensive 5X GSO Barlow and standard UV/IR filter on the camera at prime focus to capture the images, which have only been very lightly processed to show the telescope’s potential. See below.

Mighty Jupiter as captured by Adam Blake using the 130mm f/5 Newtonian on the evening of April 5, 2016.

Mighty Jupiter as captured by Adam Blake using the 130mm f/5 Newtonian on the evening of April 5, 2016.

 

 

 

 

 

 

 

 

 

 

21:30UT

I aimed the Heritage 130P at iota Leonis, now high in the south. Using 244x I was able to quite easily resolve A-B. The primary shines with magnitude +4.06 and the secondary +6.71 with 2.1″ separating the components. I would warmly encourage others to try this system, as well as the aforementioned star systems with this telescope.

A Portable Dew Buster: Are you concerned about dew building up on the open tube of the Heritage 130P? Nae worries! I never let any heating devices within a country mile of my telescopes, just like my forebears. I bought a portable three-speed fan for about £10 that zaps dew in seconds from the secondary and primary using cold air. Now you can enjoy the telescope under the stars for as long as you like!

Laudate Dominum!

 

 

 

 

 

 

 

 

 

April 28, 2016

00:30h

At an ambient temperature of -1C, the Skywatcher Heritage 130P worked flawlessly to bag epsilon 1 and 2 Lyrae, eta Bootis (with its 10th magnitude companion), pi Bootis ( AB:  4.9, 5.8  separation  5.4″ and  AC: 4.9,10.6, separation 127″), alpha Herculis ( AB:3.5, 5.4, separation 4.6″ and a corker, AD: 3.5, 11.1, separation 79″)

For lunar and planetary studies, I can also recommend the Baader single polarising filter to use with this adorable little telescope. Retailing for £32.00, it significantly enhances belt detail on Jupiter, reduces glare and presents the planet in its natural colours.

The superlative Baader single polarising filter.

The superlative Baader single polarising filter.

 

 

 

 

 

 

 

 

 

 

Sunday, May 15, 2016.

The view from the sandy beach at Luss, on the western shore of Loch Lomond. May 14, 2016.

The view from the sandy beach at Luss, on the western shore of Loch Lomond. May 14, 2016.

 

 

 

 

 

 

 

 

 

 

During a relaxing weekend away with a group of old friends in the picturesque and historic village of Luss, on the western bank of Loch Lomond, I took the little SkyWatcher Heritage 130P along with me, as it was so easy to transport and set up. After long sunny days outdoors, I set the instrument (on its Dob mount) up on the garden table for a look at Jupiter and the first quarter Moon, which were perfectly positioned in the evening sky.

The Skywatcher Heritage 130P on holiday.

The Skywatcher Heritage 130P on short vacation.

 

 

 

 

 

 

 

 

 

 

As this was an annual event away, the crew were expecting me to bring along a telescope, but it is usually of the short refractor variety. I got some odd looks from the gang as I extended the upper stage of the ‘strange’ reflecting telescope, but I was sure glad I made the effort; they were all mightily impressed by the images the little portable reflector served up:- and even more gobsmacked when I told them how relatively inexpensive an instrument of this quality cost to acquire!

That's it guys: form a nice orderly queue.

That’s it folks: form a nice orderly queue.

 

 

 

 

 

 

 

 

 

A close encounter with the first quarter Moon: Kenny's face says it all!

A close encounter with the first quarter Moon: Kenny’s face says it all!

 

 

 

 

 

 

 

 

 

 

 

July 21, 2016

 LightBridge Mini 130 5.1" tabletop altazimuth mini-Dob reflector by Meade Print Home Telescopes The Meade LightBridge. Image Credit: Meade Instruments.

The Meade LightBridge Mini 130 5.1″ tabletop alt-azimuth mini-Dob reflector
 Image Credit: Meade Instruments.

My collegaue at Astronomy Now, Steve Ringwood, has independently reviewed the New Meade Light Bridge 130 Mini Dob for the August 2016 issue of Astronomy Now (now in the shops) on page 108-10. Although a slightly different design to the Heritage 130P featured in this blog, the optics are essentially the same but features a solid tube and a more traditional four spider-vane secondary support for even more rigid collimation maintenance in the field. Steve found that the optics were very good indeed, being capable of powers in excess of 200x, in agreement with my findings. At $200, it is priced at the same as the One Sky Newtonian from Astronomy Without Borders, discussed above.

So more choice for the discerning amateur.

Brian Schultz, from his YouTube channel Cool Space, describes how the One Sky Newtonian can be fitted to an inexpensive go-to mount for added versatility. See here for a video clip.

August 8-9 2016

The Old Man of Storr, Isle of Skye, as seen in the opening scenes of the block buster movie, "Prometheus".

The Old Man of Storr (elevated in the distance), Isle of Skye, as seen in the opening scenes of the block buster movie, “Prometheus”.

Our family ventured to the remote Isle of Skye, a place of outstanding natural beauty, for our summer vacation. My trusty 130mm f/5 Heritage Newtonian travelled with us. Though the weather was mostly damp and windy, I did enjoy a bout of observing with the instrument during brief clear spells on the evenings of August 8 and 9. The sky is truly glorious at this location, presenting some of the darkest and most transparent skies in all of Europe. And the (not so) little 130mm did not disappoint, serving up jaw-dropping views of the northern Milky Way high overhead, once the crescent Moon fell out of the sky. Deep sky objects were a joy to behold, including M31,Caldwell 14, M57, M13 and M92. The North American Nebula in Cygnus was as plain as the nose on the your face, as were the eastern and western Veil nebulae nearby.

Plotina ready for action on the remote island of Skye.

Plotina ready for action on the remote island of Skye.

I can also report that high resolution targets – including a batch of close test double stars – presented very well indeed. Images of systems such as Izar, delta Cygni etc, were calm and well resolved at high powers (243x), showing that this island has good seeing conditions for such work. Scotland has many such places(as I continue to discover) if one is intrepid enough to find them out!

September 30, 2016

My experiments with the Skywwatcher  Heritage130P continue apace. A while back a kindly gentleman from the USA alerted me to a potential issue with the instrument; the loss of precise collimation as the instrument is pointed to different parts of the sky. In a series of experiments conducted over the last six weeks or so, I discovered that while tightening the shaft that holds the secondary mirror in place seems to solve this problem for lightweight eyepieces, it doesn’t always hold collimation for heavier oculars such as the rather bulky, Baader Hyperion zoom.

As a consequence, I have reassessed the suite of oculars I use with the instrument and have switched entirely to smaller, more lightweight units. Below is an image of my current experimental set up; a 32mm Plossl, delivering a power of 20x and a 2.5 degree true field. Using the tiny, screw-on 2.25x Baader Barlow, I can couple the 32mm ocular to give a power of 45x and a true field of ~1.1 degrees – just large enough to frame the entire Double Cluster in the field!

For higher power work, I use a Parks Gold 7.5mm delivering 87x, a 6mm Baader classic orthoscopic yielding 108x, and a 4mm Revelation Plossl (fully multicoated) giving 163x. Finally, using the 2.25x Barlow I can achieve 243x and even 366x when mated with the 6mm and 4mm oculars, respectively. I also have an old 1.6x screw-on Barlow made by UK Astro Engineering, which gives me still more options to play with.The Barlows will increase the eye relief of the short focal length of the short focal length eyepieces too.

Plotina with a suite of lightweight oculars and low profile Barlows.

Plotina with a suite of lightweight oculars and low profile Barlows.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Over the winter I hope to fine tune this set up some more, but I am very happy with the range of powers available to me and the relatively low cost of its operation.

I also intend purchasing some Bob’s Knobs collimating screws to fit to the secondary assembly in order to make collimation even more easy to achieve.

I will report back later in the year to tell you how I got on!

The instrument continues to inspire in so many ways and needless to say I have grown very fond of using it.

Thursday, October 13, 2016

Plotina received her new set of Bob’s Knobs secondary screws to make fine adjustments to collimation easier. I consider these to be a quality acquisition going forward.

Bob's knobs for easier adjustment of the secondary mirror.

Bob’s knobs for easier adjustment of the secondary mirror.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Monday, October 17, 2016

Upon further investigation, I have been able to tighten up the stalk holding the secondary mirror in place by inserting a small washer, as shown below.

A simple washer tightens up the secondary support.

A simple washer tightens up the secondary support.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

This increased rigidity allows the instrument to maintain precise collimation even after moving the telescope wildly in altitude and azimuth. This was verified using a laser collimator. The telescope can now use larger oculars once again, including the Baader zoom.

Monday & Tuesday, October 18 and 19, 2016

A break in the wet autumnal weather over the last two nights has allowed me to conduct further tests with the SkyWatcher 130mm f/5 Newtonian. I fielded a 90mm apochromat (retained for further testing) side by side with the instrument and studied how both performed on a variety of high resolution targets located in different parts of the sky.

Test instruments: a 130mm f/5 Newtonian (left) and a 90mm apochromatic refractor (right).

Test instruments: a 130mm f/5 Newtonian (left) and a 90mm apochromatic refractor (right).

Yesterday evening, shortly before midnight, I compared and contrasted both instruments in respect of their ability to maintain crisp, bright images of a waning gibbous Moon. Once our satellite achieved a decent altitude, I cranked up the magnifications on both instruments and examined the cratered terrain along the day-night terminator. Both instruments performed well but the larger aperture of the Newtonian allowed me to employ significantly higher magnifications (in excess of 300x) before the image became unsatisfactorily dim for my liking. The 90mm refractor, in contrast, maxed out about 200x.

Tonight, with better seeing but in colder(+4C) and hazier conditions, I ran the two telescopes to a variety of double star targets at various altitudes; gamma Delphini, theta Aurigae, Iota Cassiopeiae and delta Cygni; these systems were deliberately chosen so as to test how the 130mm Newtonian would hold collimation as it was adjusted in altitude and azimuth. My results show that the insertion of the washer in the stalk supporting the secondary mirror (described above) worked perfectly well, the stellar images remaining crisp, round and tiny. In every case, the Newtonian produced brighter, more convincing splits of these systems under equivalent magnification regimes – 200 to 250x.

These results show that the Newtonian is a wonderful, cost-effective and versatile instrument for all celestial targets and is noticeably superior to a much more expensive 90mm refractor, which quickly runs out of both light and resolving power in comparison.

I continue to highly recommend this instrument to those who are looking for excellent performance on a limited budget.

Nothing more to say really.

Thanks for following this blog.

Best wishes,

Neil.

Update: February 15 2017

My colleague at Astronomy Now, Ade Ashford, is helping to change culture by writing an excellent four page article on how to tune up the SkyWatcher Explorer 130PDS, mentioned in the blog above, and essentially the same telescope optically as the Heritage 130P (but with a closed tube) for better visual and photographic use. You can read this VERY interesting article in the March 2017 issue (page 98 through 102), out now.

Update: July 17 2017

Time: 00:09 BST

Location: Wigtown, Southwest Scotland.

Seeing: ( I to II): generally excellent, very calm

Instrument: 130mm f/5 Newtonian

Comments: A fabulous bout of double star observing. See notes below.

 

 

 

 

 

 

 

 

 

 

Update: July 18 2017

Time: 00:45 BST

Comments: Just in from another excellent session with the 130mm Newtonian. Highlight of the night was tracking down and resolving the lovely Mu Cygni. Tight pair, even at 244x and a fainter ‘companion’ wide away making it seem more like a triple system. Generous aperture and solidly good optics made very light work of this system. Like I said, this is arguably the best grab ‘n’ go ‘scope on the market today.  Details below;

 

 

Update: July 21 2017

Time: 00:35 BST

Instrument: 130mm f/5 Newtonian, aka ‘Plotina’

Seeing: Excellent (I); very clear before midnight. Some cloud moved in after midnight.

Comments: Still in Wigtown. Third night where conditions have been excellent.

Some very tricky systems resolved once again this evening with this modest telescope. Textbook perfect results!

Ashamed of my peers.

 

 

 

 

De Fideli.

Changing Culture Part IV: The Ultimate Grab ‘n’ Go ‘Scope?

Monday, December 19, 2016

Ich bin ein beginner!

As described in a previous blog, I have come to learn the many virtues of the powerful yet relatively inexpensive SkyWatcher Heritage 130P, a 5.1 inch f/5 tabletop Newtonian. I described various modifications I made to the telescope in order to optimise its performance. These included replacing the existing secondary with a smaller unit, giving a secondary obstruction of just 27 per cent. Both the primary and secondary mirrors were also treated with Orion Optics’ HiLux super high reflecting coating, providing brighter, more contrasty views of celestial targets. I also described some modifications which involved tightening up the secondary stalk holding the secondary mirror in place, which helped maintain precise collimation while the telescope was being slewed to different parts of the sky.

I can report that the telescope is still performing excellently, so much so that I now question the wisdom of using a small aperture refractor (or catadioptric) for grab ‘n’ go excursions. As explained in my blog, this telescope is very lightweight, fits on a variety of ergonomic mounts owing to the included Vixen style mounting plate, and cools super quick due to its relatively small, thin primary mirror and open tube configuration. But on the evening of December 19, I learned yet more of its secrets.

The night was cold (near zero Celsius) but the sky remained steadfastly clear from sunset to near sunrise the next day. I felt rather tired that evening, having gone through several hours of maths teaching, but I still wanted to venture out under the wintry sky before the waning gibbous Moon got up. So I turned to the 130P, mounting it on a lightweight Vixen II Porta altazimuth to get some observing in. Seeing conditions were not fantastic but perfectly adequate for most targets. The instrument was precisely collimated using an inexpensive laser collimator, as described previously, and made even easier since I installed some Bob’s Knobs secondary adjustment screws. This operation takes only a couple of minutes to execute accurately and I was then ready to reach for my Baader Hyperion zoom, an eyepiece I have grown very fond of owing to its excellent quality for its modest price. Indeed, it really is only slightly inferior to high quality oculars of fixed focal lengths. Thankfully, this is now being openly acknowledged by many amateurs on the forums. See this interesting link comparing this zoom to a much more expensive Leica zoom covering more or less the same focal length range.

The truly remarkable Mark III 8 to 24mm Baader Hyperion zoom and the light weight, low profile 2.25x Baader Barlow lens.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

In previous excursions, I reported that the zoom was rather heavy and I was concerned that it might be throwing off the collimation as the telescope was aimed at targets of varying altitude. But I can report that the addition of a single washer to the stalk holding the secondary mirror greatly increased the rigidity of the system and I felt I could chance using this large (and bulky) eyepiece as my only portal on the Universe on this frosty evening. So, how did it perform? In a word; magnificently!

The Skywatcher 130P outfitted with the Baader Hyperion zoom. Note the extended distance of eye placement from the optical train.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

But to elaborate, I discovered that the zoom keeps one’s body a few inches further back, away from the optical train, and more effectively attenuates the thermal heat plumes issuing from my body. An open tube like the Heritage 130P is significantly more sensitive to thermals introduced into the optical train, especially on cold nights like that experienced on the evening of December 19. I was actually quite shocked at how calm the images appeared in the eyepiece, examing as I did, several fairly tricky double and multiple stars, including some of my seasonal favourites, like beta Monocerotis (at a fairly low altitude), and much higher up: theta Aurigae, iota Cassiopeiae and (the less challenging) Castor A & B. All were well resolved. The native zoom provides a very useful range of magnifications from 27 to 81x, and can be further extended to a greater range of powers up to 182x (and thereby further extending the distance from the optical train). The images of all these systems were remarkably calm!

Close up of the zoom housed securely in the eyepiece holder of the instrument.

Furthermore, comparing the views through the zoom and a much lower profile 7.5mm Parks Gold ocular and Barlow, I could see that the images remained calmer for longer using the zoom. The images were quite simply less affected by anthropogenic turbulence. This is going to make a very significant difference while conducting high resolution work with this telescope during the many cold nights we experience here in Scotland. Nor did the zoom cause any miscollimation issues throughout the vigil. The stars always focused down to small, tight and round seeing disks.

Moving back to the native zoom, I visited M31, riding high in the winter sky, followed by the beautiful trio of Messier star clusters adorning the heart of Auriga (M36, M37 & M38), and from there I visited to my favourite Messier open cluster, M35, in Northern Gemini. I experienced nothing but pure joy experimenting with the right magnifications to frame these clusters using the zoom and the Barlow. I especially like the way the zoom ‘opens up’ at the lower focal length settings (to a very generous 72 degrees indeed) allowing one to soak up the beautiful hinterland around the Auriga clusters.

From there, I panned the telescope down to M42, the Great Nebula in Orion, which had, by now, all but reached meridian passage, and I ‘dialled in’ the optimum viewing magnification (about 150x as it turned out), drinking up the beautiful, crisp nebulosity surrounding the theta Orionis complex (Trapezium).

My adventure under the winter sky was a wonderful experience and only ended once I saw the vault of light emerging in the eastern sky from a rising Moon. The telescope is well able to handle this extraordinary eyepiece, enabling me to effortlessly cruise from low to high power. As I already reported, it is significantly more powerful than a 90mm apochromatic refractor (tested extensively along side the 130P over several months). It can do things no 127mm Maksutov can do, especially on low power, wide field targets, and its smaller central obstruction ensures crisper lunar and planetary views.

This grab ‘n’ go system will take your short, backyard excursions to new heights, thanks to its very generous aperture. Can I recommend this telescope and zoom eyepiece combination highly enough?

Hardly!

 

Neil English is the author of several books on amateur telescopes.

Please check out this ongoing thread on a related telescope, The One Sky Newtonian, which is still going from strength to strength.

De Fideli.

Cleaning Newtonian Mirrors.

I’ve noticed that one issue that seems to give folk concern about investing in a good Newtonian pertains to having to clean the optics every now and again. I’ve never really understood this mindset though. Having had my closed-tube 8-inch Newtonian for about 18 months now, and having clocked up a few hundred hours of observations with it, I felt it was time to give the mirrors a cleaning. Here’s how I do it:

The mirrors are removed from the tube.

Two fairly grimy mirrors

Two fairly grimey mirrors.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

First I make sure that all the loose dust and debris has been blown off using an air brush. Next, I run some cold tap water into a sink and add a drop or two of washing up liquid. The water we use here is very soft; indeed we are graced with some of the softest water in the British Isles, which also makes drinking tea especially pleasant! If your local water source is hard, I’d definitely recommend using de-ionised/distilled water.

Starting with the secondary mirror, I dip my fingers into the water and apply some of it onto the mirror surface with my finger tips, gently cleaning it using vertical strokes. Did you know that your finger tips are softer than any man-made cloth and are thus ideal for cleaning delicate surfaces like telescope mirrors?

Finger-tip cleaning of the mirror.

Finger-tip cleaning of the mirror.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Next, the mirror reflective surface is rinsed under some cold, running tap water.

Rinse the secondary with some cold tap water.

Rinse the secondary with some cold tap water.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The procedure is repeated for the primary mirror;

Gentle massaging of the mirror using the finger tips.

Gentle massaging of the mirror using the finger tips.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Rinsing the primary mirror using cold tap water

Rinsing the primary mirror using cold tap water.

The mirrors are then supported on their sides to allow them to drain excess water, and then left to dry in a warm, kitchen environment. Stubborn water droplets nucleating on the mirrors are removed using some absorbent tissue.

Washed and drying out in the kitchen.

Washed and drying out in the kitchen.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Finally, the mirrors are placed back in the telescope tube, making sure not to over-tighten the screws which hold the primary in place inside its cell. All that remains then is to accurately align the optical train, as described previously.

There we are! Not so difficult after all; and all done in about 40 minutes! The soft water doesn’t show up any significant spots after cleaning unlike hard water sources and now the optics are as clean as the day they were produced.

With a busy season of optical testing and planetary observing ahead, I know that my 8-inch will be operating as well as it possibly can. And that’s surely good to know!

Gosh!

I feel a nice, hot cuppa is in order!

De Fideli.

Further Newtonian Adventures with Double Stars.

'Plotina'; the author's ultraportable 130mm f/5 Newtonian reflector.

‘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:

  1. 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.
  2. 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 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.

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

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.

Results:

Date: 12.05.16

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.

Date: 13.05.16

Time: 00:00-00:30 UT

Seeing: II. Indifferent seeing at sunset (III-IV), improving as the night advanced (II).

Temperature: +7.5C

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.

Date: 15.05.16

Time: 22:30 UT

Seeing: II-III, clear, brightening moon, twilit

Temperature: +3.5C

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.

Date: 21.05.16

Time: 22:10 UT

Seeing: II, partially cloudy, twilit.

Temperature: +10C

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.

22:30UT

Epsilon 1 & 2 Lyrae: textbook perfect split of all four components @271x. Subtle colour differences noted between the stars.

22:45 UT

Delta Cygni: Perfectly resolved at 271x. Magnitudes: 2.89, 6.27, separation:  2.7″

Date: 22.05.16

Time: 23:10UT

Seeing: II, very good, mostly clear, twilit, bright Moon low in south.

Temperature: +9C

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.

Date: 24.05.16

Time: 00:10 UT

Seeing: I-II, excellent steady atmosphere, no cloud, twilit, cool.

Temperature: +5C

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.

Date: 28.05.16

Time: 22:45 UT

Seeing: II, good stable air for double star work, cloudless sky, twilit.

Temperature: +6C

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.

Date: 29.05.16

Time: 23:10 UT

Seeing: II, almost a carbon copy of last night. Twilit.

Temperature: +7C

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.

Battle o’ the weans. In the foreground a 90mm Apo, in the backgroud, a 130mm Newtonian.

 

 

 

 

 

 

 

 

 

 

Date: 30.05.16

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.

Temperature: +11C

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).

System:Delta Cygni

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

System;Marfik*

90mm glass: dim, elongated @208x

130mm speculum: fully resolved /brighter @271x

*Suboptimal altitude

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.

Isaiah 32:6-8

Date: 31.05.16

Time: 23:05 UT

Seeing: III; significantly more turbulent than last night. Twilit.

Temperature: +10C

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.

Date: 01.06.16

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.

Date: 02.06.16

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.

Date: 06.06.16

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 pays no attention to human hubris.

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

Temperature: +11C

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.

Date: 08.06.16

Time: 23:00-30 UT

Seeing: II, good and stable, variable amounts of thin cloud, twilit.

Temperature: +10C

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.

Date: 17.06.16

Time: 22:30-59 UT

Temperature: +7.5C

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!

Date: 18.06.16

Time: 22:30 UT

Temperature: +10C

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.

Date: 27.06.16

Time: 22:45-23:10UT

Temperature: +10C

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!

Date: 29.06.16

Time: 22:45-23:20 UT

Seeing: Excellent, I-II, gentle breeze, very little cloud, twilit.

Temperature: +8.5C

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.

Date: 01.07.16

Time:22:50-23:40 UT

Temperature: +7C

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

Date: 05.07.16

Time: 23:05-30UT

Seeing: III-IV, below average seeing, partially cloudy.

Temperature: +8C

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.

Date: 08.07.16

Time: 22:40-23:00 UT

Temperature: +12C

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

Date: 11.07.16

Time: 22:45- 23:00 UT

Temperature: +13C

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.

Date: 12.07.16

Time: 22:30-23:00 UT

Seeing: III, partially clear, cool, twilit.

Temperature: +10C

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.

Date: 13.07.16

Time: 22:30-23:00 UT

Seeing: II-III, an improving picture, though not where I would like it to be. Partially cloudy, twilit.

Temperature: +10C

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.

Date: 18.07.16

Time: 22:20-30 UT

Seeing: sultry, clouded out, midge flies by the legion, twilit.

Temperature: +18C

Poodle versus Plotina

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.

Clear Skies!

Neil.

Updates

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.

Temperature: +12C

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.

Temperature: +10C

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.

 

De Fideli.

Changing Culture III: Aperture & Resolution.

On the left, a 90mm apochromatic refractor and on the right, a 203mm f/6 reflector enjoying a bout of late evening sunshine.

On the left, a 90mm apochromatic refractor and on the right, a 203mm f/6 Newtonian reflector enjoying a spell of late evening sunshine.

 

 

 

 

 

 

 

 

 

 

Introduction:

One of the ABCs of telescopic optics is that resolving power scales linearly with aperture and light gathering power with the square of aperture. These are fundamental facts that are demonstrably true and have been used productively over two centuries of scientific applications. And yet, all the while, there has been a consistent drive in the last few decades within a section of the amateur community that somewhat erroneously links performance to absolute monetary value. This largely corrupt movement is most ostensibly seen in the refractor market, where amateurs are apparently willing to shell out relatively large sums of money for telescopes that, in terms of performance, are severely limited by their small apertures. This is a worrying trend indeed, and has led many astray within the hobby.

In this capacity, I decided to highlight the anomaly by devising a simple test which exposes this ‘peashooter’ mentality for what it is; a gross misrepresentation of basic optical principles.

Materials & Methods:

Two telescopes were set up in my back garden; a 90mm apochromatic refractor retailing at £1017 (tube assembly only) and a 203mm f/6 Dobsonian, with a retail price of £289, but with some basic modifications (97% reflectivity coatings and a smaller secondary giving a linear obstruction of just 22 per cent) which increased its cost to  approximately half that of the smaller telescope. The Newtonian was carefully collimated before use.

The telescopes were left out in the open air during a dry and bright evening when the temperatures had stabilised and were fully acclimated. Both instruments were kept out of direct sunlight. The refractor had an extendable dew shield to cut down on ambient glare, while the Newtonian was fitted with a flexible dew shield to serve the same purpose. To remove the complicating effects of atmospheric seeing, the telescopes were targeted on the leaves of the topmost boughs of a horse chestnut tree, located about 100 yards away.

Both telescopes were charged with approximately the same magnifications, in this case, a very high power was deliberately chosen; 320x. Next, the images of the leaves were examined visually, being especially careful to achieve the best possible focus, and the results noted.

Results:

The 203mm Newtonian images of the leaves were crisp, bright and full of high contrast detail. In comparison, the image served up by the refractor was much dimmer and a great deal of fine detail seen in the larger instrument was either ill-discerned or completely invisible in the smaller instrument. Though less dramatic, the same results were obtained when a larger refractor (127mm f/12) was compared with the 203mm f/6 Newtonian under similar conditions, with the latter delivering brighter, crisper images with finer detail.

Conclusions:

This simple experiment, requiring nothing more than a few minutes of one’s time and no complicated formulae or optical testing devices, clearly showed the considerable benefits of larger aperture. The images served up by the Newtonian were brighter and easier to see than those served up by the smaller instrument. Resolving power and light gathering power work hand in hand; you need decent light grasp to discern fine details and vice versa.These results were largely independent of the surrounding atmospheric conditions, as the targets were located at close proximity to the telescopes and thus had to travel through a short column of air.

These experiments were repeated with larger instruments; a 127mm f/12 refractor and the same 203mm Newtonian, with the same results, that is, the smaller instrument runs out of light faster than the larger and shows less fine detail in the images served up.

These results confirm that larger aperture is superior to smaller aperture. No amount of claptrap can change the result either. Complications may arise when the same tests are performed on celestial targets, especially during bouts of turbulent atmospheric seeing, when the larger instrument will be commensurately more sensitive. In such instances, it is the environment that introduces anomalies. But when conditions are good, the benefits of larger aperture will be seen, clearly and unambiguously. Absolute monetary value has little or nothing to do with the end result, in direct contradistinction to what is claimed by those who promote small aperture refractors in an unscientific way.

See here for further reading.

 

De Fideli

Changing Culture.

Octavius: instrument of change.

Octavius: instrument of change.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

As  I have commented on in previous communications, an urban myth has been cultivated over the years regarding the unsuitability of Newtonian reflectors in the pursuit of double stars. In the last six months or so, there are encouraging signs that more people are bucking this trend using Newtonian optics of various f ratios and in the examination of pairs of various difficulty, including the sub-arc second realm;

Exhibit A

Exhibit B

Exhibit C

Exhibit D

Exhibit E

These are but a few examples, and I can only hope that the changes will continue so that more people can enjoy this wonderful pass-time.

De Fideli

Planetary Telescopes.

The author's plnetary telescope; a 8 inch f/6 Newtonian reffector.

The author’s planetary telescope; a 8 inch f/6 Newtonian Reflector.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

But thou shalt have a perfect and just weight, a perfect and just measure shalt thou have:

Deuteronomy 25:15

Comments on planetary telescopes by established authorities** in the field over the last 130 years.

As a really efficient tool for systematic work on planets, telescopes of about 8 inch aperture cannot be surpassed. It is useless waiting for the two or three serene nights in a year when the whole diameter of a big instrument is available to really good effect. Amateurs urgently require the appliances most efficient under ordinary conditions and they will find a larger aperture of little avail until it is much reduced by a system of gagging and robbed of that very advantage which is extolled so much; namely grasp of light. The 18.5 inch equatorial of the Dearborn Observatory cost £3700, the great Washington refractor £9000, the great Melbourne Cassegrainean (reflector) of 4 feet aperture cost £14,600, and at first it would appear preposterous that a good 8.5 inch With or Calver mirror, that can be purchased for some £30 will effectively rival these expensive and elaborate instruments. Many people would consider that in any crucial tests the smaller instrument would be utterly snuffed out: but such an idea is entirely erroneous. What the minor telescope lacks in point of light it gains in definition. When the seeing is good in a large aperture, it is superlative in a small one. When unusually high powers can be employed on the former, far higher ones proportionally can be used with the latter. We naturally expect that very fine telescopes, upon which so much labour and expense have been lavished, should reveal far more detail than in moderate apertures, but when we come to analyze the results it is obvious such an anticipation is far from being realized.

From W.F. Denning’s, The Defining Powers of Telescopes, Anno Domini 1885.

The planet looks as if cut out of paper and pasted on [the] background of sky. It is perfectly hard and sharp with no softening of edges. The outline and general definition are much superior to that of a refracting telescope.

E.E. Barnard comparing the views of Saturn seen with the newly erected 60-inch reflector atop Mount Wilson, with the 36-inch Lick Refractor, Anno Domini 1908

Source: Sheehan, W. The Immortal Fire Within: The Life and Work of Edward Emerson Barnard, Cambridge University Press, pp 398. Anno Domini 2007.

Although something worth recording may be seen even with a 3-inch, the intending student of Jupiter should have available a telescope of not less than 6 inches aperture. With such an instrument a great deal of first-class systematic work can be accomplished and only the smallest of the really important markings will be beyond its reach; indeed, until only a year or two before his death Stanley Williams made all his invaluable observations with a 6-inch reflector. An 8-inch is probably adequate for all purposes; a 12-inch certainly is. The bulk of the author’s work has been done with a 12-inch reflector; and although it would not be true to say that he has never yearned for something larger when definition was superb, the gain would have been mainly aesthetic and he has never felt that anything important was being missed owing to the inadequacy of his equipment.

Peek, B.M., The Planet Jupiter:The Observer’s Handbook, Faber, pp 36-37, Anno Domini 1981.

If the aperture exceeds about 12 inches , the atmosphere will seldom allow the full aperture to be used……..Direct comparisons of performance on different occasions have revealed an 8-in refractor showing more than a 36-in reflector; an 11-in refractor surpassing a 12-in reflector; canali invisible in the Greenwich 28-in stopped down to 20 ins, but visible in an 8-inch by T.E.R. Philips; apertures less than 20 ins showing more than the Yerkes 40-in stopped to 30 ins.

From Mars by J.B Sidgwick, Observational Astronomy for Amateurs, (pp 118) Anno Domini 1971.

One of the greatest Jupiter observers, Stanley Williams, used only a 6-inch reflector, but most serious students of the planet now would look for at least an 8-inch, although a good 5-inch OG can reveal surprising detail. This is not the place to debate the relative performance of refractors and reflectors, but good resolution, high contrast and faithful colour rendition are essential. A good long focal ratio Newtonian , a Maksutov, or an apochromatic refractor is probably the best but, as in every field, the quality of the observer is the most important factor, and good results can be obtained with any reasonable instrument.

Moseley T., from the chapter on Jupiter in The Observational Amateur Astronomer, (Moore, P. ed), Springer, pp95, Anno Domini 1995.

To recapitulate: Mars is not an easy target. Because the disc is generally small, it is essential to use a fairly high power telescope if it is hoped to see anything except for the most prominent features. Of course a small telescope such as a 7.6cm refractor or a 15cm reflector will show something under good conditions, but for more detailed work a larger aperture is needed. A 20cm telescope is about the minimum for a reflector; I would not personally be happy with anything below 20cm, though opinions differ, and no doubt observers more keen sighted than I am will disagree.

Moore, P., from the chapter on Mars in The Observational Amateur Astronomer, (Moore, P. ed), Springer, pp78, Anno Domini 1995.

A 3-inch refractor with a magnification of around 50x will show the planet and its ring system, but an aperture of no less than 6-inches is needed for observations to be of value; ideally one should aim for an aperture of at least this size – the larger the better. It has been claimed that the best magnification for planetary observation is about equal to the diameter of the object glass or mirror in millimetres. To see the fine details of Saturn’s belts and ring structure, a magnification of 150x to 300x is necessary, and therefore, according to the above rule, telescopes of 150mm or more are clearly required.

Heath, A.W., from a chapter on Saturn in:The Observational Amateur Astronomer, (Moore, P. ed), Springer, pp113, Anno Domini 1995.

Seeing varies from 0.5 arc seconds on an excellent night at a world class observatory site to 10 arc seconds on the worst nights. On nights of poor visibility, it’s hardly worth observing the Moon with anything but the lowest powers, since turbulence in the Earth’s atmosphere will make the lunar surface appear to roll and shimmer, rendering any fine detail impossible to discern. For most of us, viewing rarely allows us to resolve lunar detail finer than 1 arc second, regardless of the size of the telescope used, and more often than not a 150mm telescope will show as much detail as a 300mm telescope, which has a light gathering area 4 times as great. It is only on nights of really good visibility that the benefits of the resolving power of large telescopes can be experienced. Unfortunately, such conditions occur all to infrequently for most amateur astronomers.

Grego, P., The Moon and How to Observe It, Springer, pp244, Anno Domini 2005.

As a choice for planetary observations then, there is a lot to be said for the Newtonian reflector in the 6- to 10-inch aperture range.

F.W. Price, The Planet Observer’s Guide (2nd Edition), Cambridge University Press, pp 41. Anno Domini 2000

 

It allowed visual scrutiny with very high magnifications, each time it was necessary.

Adouin Dollfus (2002) in a comment pertaining to the efficacy of the Great Meudon Refractor.

A high quality Newtonian reflector is a very powerful instrument, fully capable of superb performance in viewing the planets, when the optics are kept clean and properly aligned. They have been among the favorite instruments of serious planetary observers for many decades.

Bengton, J.L., Saturn and How to Observe It, Springer, pp57, Anno Domini 2005.

As good as my 6-inch f/9 is, the 8-inch f/6 I built soon after is crushingly superior in virtually every way — including planetary performance. This is something to keep in mind if you’re considering a long-focus Newtonian. A long f-ratio helps, but aperture is much more important. Would an 8-inch f/9 be better than my f/6? Probably. But mounting and using a scope with a tube more than 6 feet long is would be a challenge. And when the aperture gets much bigger, it’s easy to keep the secondary size small without resorting to extremely long focal lengths.

From an article entitled,The Big Red One, Sky&Telescope Associate Editor and veteran ATMer, Gary Seronik, commenting on the superiority of a 8-inch f/6 reflector over an optically superlative 6-inch f/9 reflector ‘Planet Killer,’ Anno Domini 2009.

I was once loaned a 4.5 inch refractor by the British Astronomical Association back in the 1990s; it was an excellent instrument, but the optical tube was longer than me! These days refractors come with much shorter tubes, but at considerable cost and apertures of 5 in., or more, however the cost of smaller refractors have come down in recent years. Although they look splendid, remember it is aperture(size of the telescope) that is the most important. Ideally you should get the largest telescope you can for your money.

Abel, P.G, Visual Lunar and Planetary Astronomy, Springer, pp 13, Anno Domini 2013.

All in all, if you can afford it, and if you have the room to house it in some sort of observatory, I would say go for a Newtonian reflector of 10 inches -14 inches aperture and as large a focal ratio as you can reasonably accommodate…..My second choice would be a 5 inch refractor…..having a focal ratio of f/12……or an ED apochromat ( f/8).

North, G., Observing the Moon, Cambridge University Press, pp 52, Anno Domini 2014

When Mars was closest to the Earth in August 2003, the Macclesfield Astronomical Society held a star party at Jodrell Bank Observatory with quite a number of telescopes set up to observe it. As the evening progressed a consensus arose that two scopes were giving particularly good images; my FS102 4-inch Takahashi Fluorite refractor (at around £3500, or $5000, with its mount) and an 8-inch Newtonian on a simple Dobsonian mount newly bought for just £200($300). I personally preferred the view through the f/6 Newtonian but others thought that the FS102 gave a slightly better image, so we will call it a draw. It is worth discussing why these performed so well and, just as importantly, why perhaps the others did not.

From A Prologue of Two Scopes: Morison, I. An Amateur’s Guide to Observing and Imaging the Heavens, Cambridge University Press, xiii, Anno Domini 2014.

** The author chose these individuals based on both published and unpublished observations of planets available from historical archives and/or books, and having (ostensibly) sustained these observations over many years.

                                   Relevant Physical Principles

 

Resolution:

A telescope of diameter D cuts off a wavefront and blurs a point source to an image size, I,  given by I = lambda/D (radians). This can be converted to arc seconds by multiplying this result by 206265 giving I = (lambda x 206265)”/D.

Making both units of diameter and wavelength (arbitrarily set to 5.50 x 10^-9 m)  the same we obtain:

I = 0.116/D

This is similar to the more familiar Dawes formula (expressed in inches given by 4.56/D)

Thus resolution scales linearly with aperture e.g. a telescope with a diameter of 20cm will have an angular resolution twice that of a 10cm instrument.

Contrast Transfer:

Optical engineer, William Zmek, in the July 1993 issue of Sky&Telescope magazine, analysed the effects of a central obstruction on contrast transfer, arriving at this simple rule:

Contrast Transfer of an Obstructed Telescope = Full Aperture – Aperture of Obstruction.

Consider this author’s chosen planetary telescope, a 203 mm Newtonian with a secondary minor axis of 44mm (22% linearly), the resulting contrast transfer will be the equivalent of a 203-44 = 159mm unobstructed aperture, the effects of the spider vanes being essentially negligible (~1-2 %).

This result has been amply borne out by the author’s extensive field testing.See here for details.

Larger apertures also allow the observer to enjoy a larger exit pupil, which is of paramount importance in studying low contrast details at magnifications typically employed in planetary studies. See this link to see how a consideration of the size of the exit pupil can radically change the direction of a discussion about two very different telescopes.

Light Gathering Power:

Image brightness is proportional to the number of photons collected, which in turn scales as the area of the optical surface. Thus a 20cm telescope collects four times more light than a 10cm, all other things being equal. Refractors, having no central obstruction and multi-coatings applied to the glass surfaces have the greater light transmission. Reflective surfaces exhibit proportionally less transmission to the eye due to less efficient reflection off optical surfaces. In the same article highlighted above, the author described the acquisition of ultra-high reflective coatings (and greatly reduced light scatter) to both mirrors (97 per cent). Thus the overall transmission is (0.97)^2 =0.94 and subtracting the obstructing area of the secondary reduces the overall light gathering power to ~0.9. Compared with an almost perfectly light transmitting refractor object glass, this represents a 10% reduction in light, a value that even a seasoned observer would be hard pressed to see. Thus, the author’s 20cm Newtonian has a broadly equivalent light transmission to an unobstructed refractor of equal aperture.

Atmospheric Turbulence, Seeing Error & Viewing Altitude

The astronomical seeing conditions at a given site can be well described by the so-called Fried parameter r0. We need not wade into the mathematical details to understand the basic ideas behind this model. In this scheme of events the air consists of moving cells which form due to small-scale fluctuations in both the density and temperature above the observer, resulting in the blurring and/or moving of the image. The larger these cells are (which is a measure of r0) the greater the aperture that can be profitably employed. For telescopes with diameters smaller than r0, the resolution is determined primarily by the size of the Airy pattern (which scales as 1/D) and thus is inversely proportional to the telescope diameter. For telescopes with diameters larger than r0, the image resolution appears to be determined primarily by a quantity known as seeing error and scales as (D)^5/6. So, for example, a doubling of aperture results in a 1.78x i.e. (2D)^5/6 increase in seeing error. Interestingly, while the seeing error does scale with aperture, the rate of increase is not nearly as rapid as one might anticipate. This implies that large apertures can work at or near optimally, though maybe not as frequently as smaller apertures.

Reference here.

The best estimates of r0 for typical observing sites used by the amateur astronomers seems to be in the range of 5–20cm (2-8 inches) and generally larger in the better sites at high altitude, where bigger telescopes are pressed into service. Intriguingly, r0 also appears to scale somewhat with wavelength, being as high as 40cm at 900nm(near infrared).

Reference here.

Seeing is also dependent on the altitude of the planet owing to the variation in air mass through which it is viewed. If one observes a planet at the zenith, one looks through 1 air mass. At 30 degrees altitude, the air mass through which the observer views is fully doubled and at 10 degrees altitude it shoots up to 5.6 air masses!

Reference: Morison, I., An Amateur’s Guide to Observing and Imaging the Heavens, Cambridge University Press (2014), pp 22.

In general, a long-held tradition recommends waiting for the planet to rise above 30 degrees altitude to begin to exploit the potential of any given telescope, large or small.

Taken together, these physical parameters can be used to adequately explain all of the aforementioned comments made by celebrated planetary observers over the decades and centuries.

Discussion:

Unbiased testimonies provide a bedrock upon which sound conclusions can be formulated. It is self evident that aperture plays a crucial role in seeing fine detail and it is reassuring that basic optical principles reaffirm this.

The list of British observers quoted above; Denning, North, Moore, Abel, Grego, Heath and Sidgwick etc, highlight the efficacy of moderate but not large apertures in divining fine detail on planets. The consensus appears to be that apertures of between 6 and 10 inches are most efficacious in this regard. This may be explained in terms of the size of the atmospheric cells that move over British skies, which allow telescopes in this aperture range to be exploited. My own discussions with many experienced planetary observers abiding in Britain affirm the truth of this; British skies seem to favour these moderate apertures. It is important to note that this conclusion has little to do with planetary imaging, which often employs significantly larger apertures to excellent effect.

The testimony of Gary Seronik shows that an optimised 6-inch f/9 Newtonian – which presumably would provide views rivaling a 6-inch apochromatic refractor, was comfortably outperfomed by an 8-inch f/6 Newtonian, again confirming the superiority of a little more aperture.

The testimony of E.E Barnard at Mount Wilson and Adouin Dollfus at Meudon shows that larger apertures can be used to much greater effect if seeing conditions allow. Both Meudon and Mount Wilson have enabled telescopes of 30 and 60-inches to be used visually, indicating that the atmosphere can be particularly good there and for long enough periods to permit a meaningful program of visual study.

There evidently exists regions on Earth where the seeing is poor (small r0) for prolonged periods of time, explaining why amateurs in these regions stick to smaller apertures. This in part explains the popularity of small refractor culture.

The most intriguing testimony is offered by Professor Ian Morison, also based in the UK, which, on the face of it, seems to lend more credence to small refractor culture. The reader will recall that during the August 2003 Martian opposition, a large number of amateurs, fielding various telescopes, were present at Macclesfield, England. Morison claimed that two telescopes were doing particularly well; a Takahashi FS102 Fluorite refractor and a mass produced 8″ f/6 Dobsonian and that there was no clear consensus on which was delivering the better views. Having owned several econo- and premium 4 inch apochromatic refractors (and even a gorgeous 4-inch f15 classical refractor), this author (also based in the UK) has become intimately familiar with their performance. And while they all provided good views of the planets, they come nowhere near the performance of the author’s 8-inch f/6 Newtonian, which, despite its very modest cost, proved ‘crushingly’ superior to the former.

So, Morison’s testimony presents an apparent contradiction, which must have a rational explanation.

Further investigation revealed that during the August 2003 Martian opposition, the maximum altitude of the Red Planet was just 23 degrees at meridian passage as observed from London (51 degrees North latitude).

Reference here

Since Macclesfield (53 degrees North latitude) is further north than London, the maximum altitude of Mars would only have been 21 degrees and thus was significantly below the minimum altitude recommended – 30 degrees – for planetary study. Thus, it is not at all surprising that Morison et al reached the conclusions they did.The Newtonian being more sensitive to the vagaries of the atmosphere would not have been performing optimally at that low altitude, while the smaller refractor was performing much as it always does. In addition, this author observed Mars during the same August 2003 opposition using a 20cm f/10 Schmidt Cassegrain. At 56 degrees North, the planet was only 18 degrees above the horizon at meridian passage. Needless to say, the images of Mars were nothing to write home about.

Interestingly, this author reached the same conclusion whilst comparing visual drawings of Jupiter conducted with a Celestron 8″ f/6 Dobsonian during the mid-1990s with those delivered by a 5-inch refractor in much more recent apparitions. It was subsequently discovered that Jupiter was low in the sky in Aquarius at this time, while the 5-inch refractor enjoyed views of the Giant Planet situated much higher in the sky. Last year’s Jovian apparition revealed the clear superiority of the 8-inch f/6 Newtonian over the 5-inch under these more favourable conditions.

Thus there is no contradiction; aperture rules when conditions are reasonable to good. Anomalies only arise under sub-optimal conditions – persistent bad seeing, low altitude viewing etc – or if one telescope has not fully acclimated when the other has etc, hardly a fair test.

This author has brought the reader’s attention to the efficacy of a modified 8-inch Newtonian on all types of objects; deep sky, planets, lunar and double stars. These testimonies provide further evidence that such an aperture – 20cm – is probably optimal for British skies and many other environs besides.

De Fideli

An Evening with Octavius.

Octavius, my 8 inch f/6 Newtonian in the Cold of Mid-Winter.

Octavius, my 8 inch f/6 Newtonian in the cold of mid-Winter.

 

 

 

 

 

 

 

 

 

 

Prove all things; hold fast that which is good.

                                                                                1 Thessalonians 5:21


Date: Saturday, December 12, 2015

Time of observation: 22:00-23:30 UT

Temperature at commencement: -3C

Temperature at termination: -4C

Seeing: Ant I -1.5, transparency excellent, no wind.

Instrument: Well-collimated 20cm f/6 Newtonian (22 % CO). Standard Skywatcher Dob focuser. No fans employed.

Materials & Methods: A suite of double stars observed with the Newtonian, being mindful of magnifications used, aesthetics of the image garnered, and efficacy of the splits on a range of systems of varying degrees of difficulty. Mark III Baader Hyperion Zoom and dedicated 2.25x Barlow, 1.25″ Baader Neodymium filter, Parks Gold 7.5mm ocular. Instrument sat upon a Lazy Suzan Dob mount (undriven). Instrument moved from a warm and dry domestic setting to a cold and dry unheated shed, where it remained for several hours until its deployment at 22:00 UT. Flexi-dew shield attached.

Observations: One good night can dispel a myth and expose a fallacy. This time it pertains to the notion that small refractors are better suited to winter viewing and that reflectors or compound, catadioptric instruments can only do useful work in the warmer months of spring and summer.

This is a misleading notion and simply untrue. Nor is it supported by the weight of historical evidence, which shows that large Newtonians were used to great effect by some of the finest and most admired observers of past generations. The work of the great Victorian, Reverend T.W. Webb, is just one example. As we have explored previously, Webb chose to use a 9.25” With-Berthon silver-on-glass reflector to carry out observations in all weathers, including freezing winter nights. Nor did Webb employ active cooling to his telescope as no such device was available for him to use.

Octavius, my 8-inch f/6 Newtonian (also without active cooling fans) performed flawlessly this evening when turned on a variety of double stars, the Airy disks of which were observed as tiny, round, calm and beautifully resolved. Despite the large temperature differential between my body and the surrounding air, a warm insulating coat, gloves and hat greatly reduce heat loss. Attaching a dew shield to the end of the tube increased the distance between my body and the entrance pupil. All these measures and a steady atmosphere conspired to produce arguably the finest images of double stars I have seen in any telescope.

theta Aurigae: Very easily resolved at 160x but even more compelling at 360x, both the primary (magnitude 2.6) and secondary (magnitude 7.6) separated by about 4 seconds of arc. This system can be quite tricky, owing to the large magnitude differential between the components. A magnificent sight!

Rigel: Despite its low altitude, the exceptionally calm air made seeing the feeble spark from its companion child’s play at 60 diameters or above.

The theta1 Orionis complex: The 8-inch speculum showed all six of the Trapezium stars A through F at magnifications of 360x, the magnitude +11 E and F components becoming ever more distinct as one’s eyes became better adapted to the dark.

Alnitak: The easternmost star in Orion’s belt. The 8-inch telescope at 150x showed its whitish, magnitude 3.7 companion just 2.5” away to the south southeast of the magnitude 1.9 primary.

Mintaka: Very easy at all powers. The primary shines in a soft white colour but the companion, located a decent 52” away to the north presents as a beautiful, pale blue cast in the 8-inch speculum.

eta Orionis: Much more challenging but the decent aperture made very light work of this system at 360x. The telescope showed its very tight companion a mere 1.8” east northeast of the primary. This is a fetching colour-contrast double, faithfully rendered in the perfectly achromatic reflector, with the primary appearing yellow and its companion blue.
32 Orionis: The pair was perfectly resolved at 360x.The primary (magnitude 4.4) and its secondary ( magnitude 5.7) separated by 1.8”

52 Orionis: a classic Dawes pair of 6th magnitude luminaries, brilliant white and well separated by 1” using a magnification of 360x.

42 Orionis: Very impressed with this system, which was not as difficult as I had anticipated! Though only separated by 1.1”, the difficulty here is the very large brightness differential between the primary and secondary (4.6/ 7.5), the raw resolving power of the 8-inch aperture (360x) in these excellent conditions rendering the split easily.

eta Geminorum: The icing on the cake on this frigid evening! I have given mention to this orange variable star (magnitude ~3.5) in previous communications. Although I have glimpsed (and I mean glimpsed) the very faint secondary in 4- and 5-inch refractors as well as 17cm f/16 Maksutov at very high powers, the image in the 8 inch reflector was in a completely different league! My notes from the evening of January 29, 2015, using a 17cm Maksutov Cassegrain revealed the companion using a glare-reducing variable polarising filter at 340x and at a recorded temperature of -5C. That being said, the superior resolution of the 8 inch speculum was all too obvious to my eye, for it revealed the dim (magnitude 6.5) bluish secondary just 1.6” off to the west-southwest of the ochre primary more plainly than I have ever seen before in any telescope! And this was true even though the system was still a few hours away from meridian passage! The superiority of aperture being abundantly apparent, I watched eta for many minutes, savouring the sight which I had dreamed of seeing for many years.

Concluding Comments: Despite the cold, the Newtonian telescope worked perfectly well. Laziness and wilful scaremongering have prevented many from using their larger Newtonians to good effect under these conditions. The observations made this evening reaffirm the importance of aperture-dependent resolving power working under ideal meteorological conditions. They are supported by three tiers of evidence; physics, history and personal experience. Don’t let anyone stop you from discovering the genius of Newtonian optics! If you don’t try, how will you ever know? And as to the wisdom of confining one’s observations to aperture-limited refractors in winter, that’s all well and good, but bear in mind that you’ll be missing out on golden opportunities to see more, much more!

 

De Fideli

 

Taking Back Visual Astronomy II: Resolving Binary Stars with Newtonian Reflectors

Octavius the Progressive.

Octavius the Progressive.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 De omnibus dubitandum

The Newtonian reflector has a long and distinguished history among dedicated observational astronomers. With the advent of generous aperture, silver-on-glass mirrors in the late 19th century, many more amateurs could enter the field and make valuable contributions to the study of the Moon and planets. What’s more, their comparatively enormous light gathering power compared with traditional refractors made it possible to see new morphological details of hitherto elusive deep sky objects, thereby aiding in their classification.

The traditional instrument of choice in double star astronomy has been the classical refractor. With their long, native focal lengths and excellent thermal stability, they are especially adept at separating point sources at very high magnifications, at or near the theoretical limit imposed by their aperture. Refractors don’t scale well though and become impractically cumbersome and expensive in apertures above 6 inches (and if you really want to do sub arc second work you’ll need something larger anyway). I have demonstrated in earlier work that more economical telescope designs – the Maksutov Cassegrain in particular- can be excellent double star instruments. Having used a large, 17cm f/16 Maksutov continuously for a year, this author debunked a long standing assumption about these telescopes that prevented many from exploring their considerable charms. Specifically, some prominent amateurs, perhaps in some desperation to justify the purchase of much more expensive refractors, cultivated the idea that large Maksutovs (and, by implication, other catadioptrics) would not acclimate. This assertion was found to be largely unsubstantiated, after extensive field testing showed that these instruments can and do work well, even in winter.

In more recent times, this author has begun to explore anew the many attributes of the Newtonian reflector. As described in an earlier review lasting about six months, a closed-tube 8” f/6 Newtonian reflector was found to cool quickly (typically 40 minutes for a temperature differential of 20C) – significantly faster than even a 5 inch refractor. What is more, no cooling fan was deemed necessary and the telescope offered up excellent, high resolution images of planets like Jupiter. What was most surprising however, was its ability to split tricky double stars when contemporary wisdom said otherwise. This led to further investigation by examining the historical literature in order to establish whether Newtonians were ever used for double star astronomy and, if so, how efficacious they were in this capacity.

Having explored the life and work of the Reverend T.W. Webb (1806-1885), it came to my attention that the celebrated 19th century observer had indeed used a large 9.25 inch f/8 silver-on-glass reflector made by George With to resolve very tight pairs at or close to the limit imposed by its aperture. As a follow up, double star observer, John Nanson, alerted me to the work of an obscure British 19th century observer – Kenneth J. Tarrant – who employed a 10.25 inch Calver reflector (probably a f/7 or f/8 relative aperture) during the 1880s and 1890s to not only observe double stars, but to measure them also!

I would invite you to examine the documents presented here, noting the dates and seasons when the measures were made, thereby providing information on the frequency and likely conditions (like English summer temperature swings) under which observations were conducted – as well as the measures themselves, some of which show that the mirror was indeed capable of resolving pairs at or near the theoretical resolution of the telescope. I canvassed the opinion of the double star expert, Bob Argyle, based at the Institute of Astronomy, Cambridge, for his take on Tarrant’s data. Specifically, I asked Argyle whether there was anything in the Victorian amateur’s data that would stretch credulity, calling his attention to Tarrant’s measures of 25 Canum Venaticorum.

“As far as I can see, looking at Tarrant’s results, these are what I would expect from a good Calver telescope – in fact he did not seem to stretch the telescope very often. Specifically 25 CVn looks very plausible – the current WDS mags are 5.0 and 7.0 so it’s somewhat brighter than the values Tarrant gives (and currently at 1″.7).”
Tarrant’s measures demonstrate three things;

1. The British climate allowed him to frequently work to very high standards, which included sub arc second pairs.
2. The Calver reflector must have produced images stable enough for mensurative purposes.
3. Tight pairs with very significant brightness differences (up to two or three stellar magnitude differences) were also resolved.

Not much else is known about Tarrant however. “I don’t know of any other references to Tarrant’s work, “ said Arygle, “but he seemed to hold the BAA Double Star Section together before WWI finished it, and probably deserves a paper from one of the historical groups.”

In more recent times, a number of other observers using Newtonian reflectors have come to the fore. This author has already brought to your attention some of the ongoing work of Christopher Taylor, who employs an open-tubed 12.5 inch F/7 Calver reflector to watch a number of sub-arc second pairs moving rapidly in only a few years. You can see a few images of his telescope here. In addition, I am mindful of the work of the French double star observer, Jean-Francois Courtot, who has resolved pairs down to 0.66” using his homemade, 8-inch Newtonian since 1993.

It would also be worthwhile considering the portfolio of the well known astronomical artist, Jeremy Perez, who has sketched many double stars using both a 6″ f/8 and a 8″ f/6 Newtonian reflector, as well as the observations of Mircea Pteancu, who has used a 8″ f/6 reflector to successfully resolve sub-arc second pairs.

Thus, not only is there a historical precedent for the use of the Newtonian reflector in doing the kind of work traditionally associated with the classical refractor, but the notion that the former instruments would only be capable of such work in tropical or temperate climates is not supported by the evidence.

That said, not all Newtonians are equally well favoured to carry out such work!

To see why, we need to explore aspects of the physics of the Newtonian telescope.

Modern parabolic mirrors of decent quality are (or should be) essentially devoid of spherical aberration. The main optical defects in the Newtonian are due to other Seidel aberrations, particularly coma and astigmatism. Let C represent coma and A represent astigmatism.

Mathematically, the angular expansion (theta) of the image due to coma is given;

C = 3theta/(16F^2) where F is the focal ratio (relative aperture) of the telescope.

Astigmatism is given by:

A = ( D/2f) tan^2(theta), where f is the focal length of the telescope.

Since D/f = 1/F and if we consider small angles, where tan (theta) expressed in degrees ~ theta radians, the formula for astigmatism simplifies to;

A = (theta)^2/2F.

We can see from the formula for both C and A that coma (C) scales proportionately with theta while A scales as (theta)^2, so that for very small angles ( << 1 radian) it follows that coma will always overwhelm astigmatism in any properly executed mirror.

Let us now set the resolution of the telescope to the Dawes limit (in arc seconds) given by 4.56”/D
To convert this formula to radians, we need to do some more arithmetic.

1 degree = 60 x 60 = 3600”

Also 1 angular degree = 1/57.3 radians =0.017 radians

Thus if 0.017 radians = 3600” then 4.56” = (0,017/3600) x 4.56 radians = 2.21 x 10^-5 radians

So the Dawes formula expressed in radians is:

(2.21 x 10^-5)/ D where D is in inches.

For critical work at maximum resolution we may equate the expressions for coma and astigmatism with the Dawes limit;

Thus,

A + C = (2.21 x 10^-5)/D

But since A << C for any small angles (which is appropriate here), we may simplify this to just:

C = (2.21 x 10^-5)/D

Thus, since we have C = 3theta/(16F^2)

We get: (2.21 X 10^-5)/D = 3 theta/(16F^2).

Cross multiplying and rearranging, we obtain:

Theta = (16F^2 x 2.21 x 10^-5)/3D

Simplifying gives theta (in radians) = (1.18 x 10^-4 x F^2)/D

For convenience, we can now convert this formula to arc minutes;

1 arc minute = 1/60 degree = (1/60) /57.3 = 2.9 x 10^-4 radians

So, 1.18 x 10^-4 = (1.18 x 10^-4)/ 2.9 x 10 ^-4 = 0.407

Thus our final result is that

Theta (arc minutes) = (0.407F^2)/D.

We are now in a position to analyse what happens when we use various different numbers for the focal ratio (F). The formula predicts that for a constant aperture D, the maximum available field (theta) over which the image contains no appreciable aberrations scales as F^2.

This means that the faster the F ratio, the smaller the true field over which aberrations are minimized.

For example, a 8 inch f/6 mirror would have an optically corrected radius of (0.406 x 6^2)/8 = 1.83 arc minutes or 3.66 arc minutes in angular diameter. Doing the same math for F=5 and F=4 yields diameters of 2.54 and 1.62 arc minutes, respectively.

To see how this impacts work at the eyepiece, consider my own telescope, a 8” f/6 Newtonian. In order to get adequate image scale for sub-arc second pairs, I like to use a magnification of 548x (3.5mm Baader zoom and 1.6x Barlow). Since my eyepiece has an apparent field of 72 degrees, the true field available at this magnification will be 7.88 arc minutes [ that is (72/548) x 60]. Thus, the percentage (linear) of the field that gives perfect definition will be (3.66/7.88) x 100 ~ 50 per cent. When we get to an F/5 system, the percentage falls to just 30 per cent, and at F/4, a pesky 20 per cent!

One can see that at F/5 or faster, positioning the image of the double stars will become problematical, but that’s not the end of the story!

As anyone familiar with the operation of a Newtonian will tell you, the lower the F ratio, the harder it is to collimate the optics accurately. Indeed, the sensitivity to mis-collimation (a quantity called primary mirror axial error) in millimetres is given by the 0.022 x F^3. It follows that the wiggle room for a F/6 Newtonian will be a comfortable 4.8mm but just 2.8mm at F/5 and only 1.4mm at F/4!

What does all this mean?

In a nutshell, the faster the F ratio of the primary mirror, the smaller the true field at any given magnification that is truly free of aberrations and the greater the likelihood of mis-collimation. I was being kind when I described the result linearly; but when you recognise the relevant field area (which scales with r^2), you suddenly realise you’re in deep water. X marks the spot! LOLl

These are the principle reasons why an F/5  or faster Newtonian will be less likely to resolve to the Dawes limit. F/6 is about good enough – thank goodness for small mercies! – and anything slower is a bonus!***

This also agrees with my own experience, having never satisfactorily resolved sub arc second pairs with an F/5 or F/4 Newtonian. It also agrees with the aforementioned historical curiosities!

Look again at Tarrant’s measures of 25 CVn conducted in the summer of 1885.

Octavius; a ‘scope to believe in!

***Note added in proof: The above calculations do not preclude the possibility that a precisely aligned, fast Newtonians (f/5 or slower) can’t do this type of work  but rather serve to illustrate that the difficulty of achieving these high resolution results becomes more difficult as the F ratio falls. Investing more money in precision focusers and more exotic collimating devices can increase the odds of success, as could the possibility of introducing optical accoutrements like coma correctors (now being made by various manufacturers) into the optical train.

References

Bell, L The Telescope, Dover (1971)

R.W. Argyle (Ed.) Observing and Measuring Visual Double Stars, Springer (2012).

Results so far: In the last six months or so, I have had the privilege of using this fine SkyWatcher 8-inch f/6 Newtonian reflector. As explained in an earlier review, I modified the instrument by purchasing a smaller secondary mirror (22 per cent by diameter) made by Orion Optics, Newcastle Under Lyme, England. I could have reduced this further but I wanted the telescope to be an excellent all-rounder rather than just a one trick pony. Both the primary and the new secondary were treated to enhanced Hilux coatings, which significantly increased its light grasp, reduced scattered light around images and has a longevity that is guaranteed for at least 25 years. Such an instrument provides breath-taking views of the Moon and planets and serves up a 2.25 degree true field for stunning deep sky vistas.

Even before I had these modifications done, I was very impressed by its ability to resolve some tricky doubles and triple systems. On the best nights, stars present as tiny Airy disks, round as buttons, even at very high powers ( > 500x). The spherical correction of the mirror is excellent and displays no on-axis astigmatism, which is a definite show stopper for this kind of work. My best images yet came just a few nights ago, where on the mild evening of Friday, June 26 at 22:20 UT, I beheld the most striking image of Epsilon Bootis (340x) I have seen in just about any telescope! The components – a soft yellow primary and a royal blue secondary – were magnificently rendered with acres of dark sky separating them. The same was true when I examined Delta and Mu Cygni, as well as Pi Aquilae (1.5″); text book perfect renderings if ever I have seen them!

At twenty minutes past midnight on the morning of June 9 last, I managed to glimpse the elusive companion to Lambda Cygni (my best yet at this location, 0.9” and 1.6 stellar magnitude differential), convincing me that I could go still further.

My methodology is fairly straightforward and is based on the recommendations of Christopher Taylor, who I mentioned earlier.

• The telescope is checked for accurate alignment using an inexpensive laser collimator before the commencement of each vigil and backed up by careful star testing.

• Only stars above a certain minimum altitude are examined, not less than 35 degrees

• I use a Baader Neodymium Moon and Sky Glow filter, which darkens the twilit sky at my location, reduces glare from very bright stars, and retains a neutral colour balance.

• After charging the telescope with the appropriate optical power, the stellar image is swung to the east of the field and left to drift slowly into the centre, where it is critically examined by my eye. The above is repeated again and again until I am satisfied that what I am seeing is not a diffraction artifact or some such.

• The time, date and conditions, magnification etc are always recorded. And if at first you don’t succeed……. try try again Lol!

In my correspondence with Bob Argyle, he was kind enough to suggest two stellar systems which are especially ripe for study with the 8-inch speculum; 78 UMa, now conveniently located near the bright star Alioth in the Plough Handle (components have magnitudes 5.02 and 7.88, with a current separation of ~0.8”) and Tau Cygni (magnitudes 3.38 and 6.57 with an angular separation of 0.9”).

I will begin with 78 UMa, as it should be fairly easy to find near Alioth in the twilight.  I shall leave Tau Cygni to later in the season.

I will report back on my progress in due course.

If you have a similar ‘scope at home, why not give it a try too?

If these stars are not suitably located for you, seek out others of similar difficulty by looking up the WDS catalog.

This project will certainly tax your powers of observation.

It would be great to hear about your experiences!

 July 1, 2015

NB: Taylor used a ‘routine’ magnification of 825x with his 12.5 inch f/7 Calver to achieve separations of 0.35 -0.40″ pairs. May attempt slightly higher powers on my own (smaller, 8 inch) telescope, perhaps 600x plus?

Nae luck as yet. A heat wave has settled in over the UK. While southern Britain basks in sunshine, conditions have remained stubbornly sultry with lots of cloud hampering any attempts to track down UMa 78.

Attempted a brief vigil late in the evening of Friday, June 26. Although my ‘easier’ test systems mentioned above all looked excellent, cloud prevented me from locating  my target near Alioth. I did however ‘uncover’ a delightful new binary system about half a finder field away from Alioth; STF 1662 ( RA  12h 36 min, Dec: 56 34, magnitudes 7.83 an 9.75, separation 19.3″).

Just received word that my article on modifying the SkyWatcher Skyliner 200P will be featured in the August 2015 issue of Astronomy Now………hallelujah!

July 2, 2015

Time 22:50h UT

Ambient: Clear, good transparency, 14C, slight SW wind, strong twilight, seeing not so hot (Ant III-IV), midge flies legion.

Four ‘warm up’ systems  observed @ 340x

Epsilon 1&2 Lyrae: well resolved.

Epsilon Bootis: resolved with some distortion.

Delta Cygni: Companion seen periodically, but with some considerable distortion.

Pi Aql: Resolved fairly well but only occasionally.

A 1.5″ night. Little point in continuing. Packed up early.

 July 4, 2015

Happy Holidays to all my viewers in the United States!

Moi?

Semper eadem.

Weather still rather unsettled, very humid with lots of heavy down pours, so little else to report from my own observations.

Investigo: I love data and admire diligence. Though I don’t know him from Adam, the American amateur astronomer, Mr. Tom Bryant, gave me both in bucket loads!

Mr. Bryant has been very busy testing the performance of his C8 on hundreds of double stars from all across the heavens.

You can see the fruits of his considerable labours here.

Go on; have a good, long look at that huge list. Dates (all year round!!!), times, instruments, are recorded, and, crucially, the location of those observations.

Input! Input! Input!

Lol!

And I see he’s constantly updating (see the latest dates listed).

Way to go!

He’s done remarkably well on many sub-arc second pairs don’t you think?

0.7″ doesn’t seem too much of a stretch for him and he’s elongated pairs down to 0.5″!

Here’s a recent review of a modern C8.

This instrument has a central obstruction of ~ 35 per cent and takes a while to acclimate…. apparently.

Here’s  the climate data for Bethesda, MD, which is quite near Silver Spring, MD, where Mr. Byrant uses his C8 inside his cosy, wee observatory, Little Tycho.

Typing in the months, one by one, we see diurnal swings of about 10C throughout the year, and which is a little larger than those encountered at my location.

My 8″ f/6 Newtonian, with a 22 per cent central obstruction, ought to do just as well – if not better – would you not think?

Only the seeing and my laziness can limit its performance.

Surely?

 July 5, 2015

Some thoughts on a lazy, Sunday afternoon:

The diligence of Tom Bryant and Carlos has delivered treasures to them. Work pays.

God endowed King Solomon with wisdom because he desired it ahead of wealth and power.Still, because of his faith, the Lord gave Solomon all three, and in great abundance.

Yet, he was better at dispensing that wisdom to others than applying it to himself.

In the proverbs of that ancient King, we learn of the traps laziness sets for us;

No matter how much a lazy person may want something, he will never get it. A hard worker will get everything he wants. 

Proverbs 13:4

A lazy person is as bad as someone who is destructive.

Proverbs 18: 9

Why don’t lazy people ever get out of the house? What are they afraid of? Lions?

Proverbs: 26:13

Nuff said, eh?

20:30 UT

At last, another opportunity will likely present itself later this evening to visit 78 UMa.

With a bit of luck, I’ll have more to report back on soon enough.

But let’s not confuse ourselves. There is one telescope forum in particular that harbours a few lazy liars I’m in the processing of flushing out.

Folk who masquerade as being ‘experienced’ but ostensibly reveal very little of that quality. Nor do they show any real insight except that which they borrow from others.

They neither understand their observing environment, nor the kinds of instruments that would best work there. e.g. using a large, fast reflector to split low-altitude double stars in a desert?!

How dumb is that? Lol!

But this is just ignorance, and I’m willing to overlook that.
That said, there’s a more insidious side to all this, which I am not willing to overlook.

Lies, lies, porky pies.

You see, some individuals spend their time cultivating untruths about what can and can’t be done with certain telescopes, without ever testing these claims in a scientific way.

Worst still, they persist in maintaining these myths, despite the mounting counter-evidence presented to them.

I suppose it’s a form of blindness.

Why shouldn’t a Newtonian deliver the readies?

If you know, tell me; I’m all ears!.

iustitia! iustitia! iustitia!

July 6, 2015

00:20h BST.

Ambient: Mostly clear, tranquil, cool (10C), twilit.

Seeing: II-III

A better night tonight. Seeing fairly good.

All warm up systems beautifully resolved at 340x

0.9″ companion to Lambda Cygni well glimpsed at 548x during moments of better seeing

78 UMa: diffraction pattern examined on and off for 20 minutes at 548x. Higher powers found to be unhelpful. Companion unseen.

Heavy dew this evening.

Good, productive night, all in all.

22:25UT

Teeming down with rain tonight.

Thus far, it’s not the kind of Summer we enjoyed last year.

Still, when are two ever the same? lol

Moi?

Semper eadem.

It occurred to me that I’ve already achieved what I set out to demonstrate; that a decently executed Newtonian can be used to explore the dynamic realm of sub-arc second binary star astronomy; I mean, I’ve already bagged (a few times now) a 0.9″ with a sizable brightness differential (1.7), so anything beyond that just reaffirms my premise.

But I don’t think I’m being overly ambitious to work for something better. Do you?

I will continue to work with 78UMa until the skies get darker.

July 8, 2015

00:30h BST

Test everything; hold fast to what is good.

                                                                   1 Thessalonians 5:21

Ambient; mostly cloudy, 13.5C, a few patchy sucker holes opening and closing. Breezy (7mph westerlies).

Seeing: II, certainly a notch up on last night.

Only three test stars examined tonight; all images at 340x were clean and crisp but shaky in the wind.

Spent a few minutes on and off examining 78UMa at 340x and 544x. Complex diffraction image, no elongation observed at 544x, so the companion must be ‘disembodied’ from the primary (Airy disk round as a button). Wind and cloud making detailed observations very difficult. Companion unseen.

I have noticed, going back through my notes, and again tonight, that on windier evenings, the images through the Newtonian can look especially fine. I have thought about why this might be. Perhaps the breeze circulates the air inside the tube more efficiently and might be ‘brushing off’ any boundary layer that might be on the mirror?

I think there is something in this.

Mother Nature lending a helping hand, just as she must have done with other observers using their specula over the decades and centuries.

Thank goodness for the wind!

09:50h BST

Last night was most interesting. Not much in the way of systems observed but the quality of the images in the modest wind was duly noted.

It was such a simple revelation to me that I cannot help but think it is universally true.

My previous observing records with refractors and a large Maksutov have shown that good to excellent seeing can accompany windy weather. I look back fondly at the wonderful skies of last Summer, where I got superb results with a 17cm Maksutov. I note especially my observations made on the evening of July 16, 2014, where the Maksutov cleanly resolved Lambda Cygni  during a windy (9mph) spell.

In the case of the Newtonian, I think windy conditions can have additional benefits in improving image quality, independent of the seeing.

Open air observing with Newtonians appears to be a good thing and I shall continue with this custom.

Might a fan be beneficial?

Maybees aye, maybees naw.

Would I consider installing one?

No.Ohxi.

I get enough breezy evenings in a year to continue as I am.

Besides, I am willing to bet that the foolishness of the wind is smarter than the ingenuity of any man-made fan.

A curious aside: Our Victorian friend, Kenneth J. Tarrant, observed 25 CVn with his Calver reflector on the 189th day of the year. Curiously this was July 8, 1885 – almost exactly 130 years ago today!

LoL!

I found some old British archives for the general weather for that month here.

I note that in this meteorological document, for the dates July 7-11, there were ‘favorable South-westerly winds in most places’.

Might  Mr. Tarrant have enjoyed a few breezy evenings when he made these measures?

I wonder!

July 9, 2015

00:20h BST

Ambient: Clear, cloudless sky, very beautiful twilight, no ground wind, unseasonably cold (6.5C), seeing III-IV. Cool Arctic air flow tonight; bright stars scintillating strongly.

Test systems all resolved, but the more difficult ones not so cleanly. U78Ma examined at 340x an 544x but too turbulent to study.

Vigil aborted.

11:20h BST

I have been thinking about the wind again and how best to use it. When Mr. Tarrant observed 25 CVn, his telescope would have pointed westward, towards Canes Venatici, and if there were a southwesterly breeze during the time he observed the system, some part of it would have blown over his Calver primary mirror.

This immediately presented a simple activity that I could use profitably during breezy evenings. When first placed outside, I could remove the cap that covers the front of the instrument and point the telescope directly into the prevailing winds. That way, the air would be blown over the mirror and it would help expel any ‘stagnant’ air inside the tube.

When observing an object in a part of the sky away from the natural direction of the wind for any prolonged period of time, I could swing the instrument back into the natural air flow  periodically, for a minute or two perhaps, before resuming my work.

I did some searching this morning to ascertain if anyone had recommended this procedure, either in printed texts or online. To my astonishment, I came up with nothing.

Maybe you know better?

In addition, I have been looking at images of those silver-on-glass reflectors of old (existing before the era of the electric fan) and noticed that many of the tubes have little hinged  ‘windows’ at the side, near the primary mirror, so as to assist (presumably) the circulation of air in the optical train. I may consider something along these lines myself; perhaps drilling a coupe of small holes on opposite sides of the tube and fitting a fine wire gauze over them to enable air to flow through but not particulates.

I can make the wind work harder for me.

Something to think about anyways.

To my chagrin, more unsettled weather is forecast for the weekend ahead.

Mair anon..

July 13, 2015

23:45h BST

Ambient: almost entirely clear, tranquil skies, seeing excellent (I-II), 10C, humidity high.

Success!

Started on Delta Cygni (340x) and was rewarded with a beautiful calm image! Companion resolved from its primary by a veritable country mile.

Pi Aql: Very cleanly resolved (340x) even at less than optimal altitude.

78UMa: Companion seen fairly well, roughly due east of the primary and inside first Fraunhofer diffraction ring. Glimpsed at 22:50h but better seen at 23:30h.  Checked the WDS data on the system Der Admiral sent me the other week. Its estimated position angle of ~118 degrees agrees fairly well with my observation.

No’ bad ken.

Where next Columbus? LOL

Anyone following me?

Vigil ended owing to heavy dew.

July 14, 2015

Bastille Day, New Horizons hurtles past Pluto, ken.

20:00h

Consummatum est.

No more to prove. No more work to be done. No one left to fight.

A 8 inch f/6 reflector can indeed be used to resolve sub arc second pairs. You don’t need an expensive telescope to do it.

A little preparation and the determination to succeed is all that is required.

And one good night.

I contacted Bruce MacEvoy, who I had the pleasure of meeting in California a few years back. He will be editing a brand new edition of the Cambridge Double Star Atlas. Bruce followed my work with the Maksutov and, more recently, the Newtonian reflector. After congratulating him on his new role, I reminded him that he had a responsibility not to cultivate untruths about the types of telescopes that can and cannot do high resolution double star work. He assured me that the atlas will not endorse the fallacy that one type of telescope is superior to others.

Satis.

Nota Bene: November 29, 2015: Dave Cotterell, based in Ontario, Canada, posted a string of high resolution images of double stars – some quite tricky for any telescope – using his 12.5″ f/6.5 Newtonian, thereby providing more evidence that these instruments can and do make excellent double star ‘scopes. In addition, he has reported his visual results here, using the same instrument, showing that he was able to cleanly resolve pairs down to 0.5″ or  0.6″. Well done Dave!

De Fideli