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CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.
Why the tests?
While other scopes in varying sizes and specifications have come and gone from my collection over the years, the above scopes are among five which have stayed, and these two have been the nucleus of my battery and in constant use for many years.
Their general optical quality has been rather well established via countless observations, but while they have been used extensively in side by side testing of eyepieces and other components, strangely, I never compared these scopes against each other until now.
The purpose of this evaluation was to establish the comparative overall quality of these scopes, as part of the process of determining my long term telescope battery. The result was also to help determine what, if any, other scope purchases may be required to deliver my long term telescopic needs.
OK! You've got me!!! I should have said my long term telescopic lusts!
This was a lightly structured test. I set up the scopes, and used all my (30+) eyepieces in each scope, taking care to compare views using as close to identical magnifications, as focal length and eyepiece selection allowed. Basically, in addition to general optical comparisons at various magnifications, I tried to determine just how much magnification each scope can deliver and still display a quality image. This process would, I hoped, deliver some overall qualitative enlightenment on each scope's capability. If atmospheric conditions permitted, I planned to do critical star testing of each scope's optics. As it turned out, the atmosphere never became calm enough to complete this objective to the degree of accuracy I wanted, so this objective remains only partially fulfilled (based on earlier individual tests).
Meade 8" f/6 Equatorial Newtonian
This scope has been so fully modified and upgraded over the years, it's a stretch now to call it a Meade. The equatorial mount and (horrors!)AC drive unit, circa 1982, is still original. The fiberglass tube and primary mirror cell are still original. Depending on what I'm doing, the optics may or may not be Meade. I have spare primary and secondary mirrors, and I tend to swap them in and out of the OTA fairly regularly. Multiple primary cell mounting holes in the fiberglass tube, and a focuser with slightly more than average travel, allow for the slight variations in focal length between mirror sets.
During these tests, I had the original Meade primary mirror and a Lumicon enhanced aluminum secondary in it. The secondary is in a Novak Research Grade holder supported by a Novak Research Grade 4 vane spider assembly. The focuser is a Telescopics Sky Micro combination rack & pinion and helical focuser. Rough focus is achieved by using the conventional knobs, then fine tuning is done by twisting the focuser barrel. Unique, and surprisingly precise!!!
This scope delivers images that rival refractors (I said rivals, I didn't say equals). In many observing sessions, it equals or beats the 10" SCT on lunar & planetary detail. On star clusters, it's close between the 10" and 8", but the contrast and pinpoint stars across the field (using a Paracorr) give the 8" a slight edge. On faint fuzzies, the 8" delivers nice clean, contrasty views, but the 10" still wins.
It was with this 8" that I first discovered that there were actually six stars in Orion's Trapezium, before I actually knew E & F existed. This scope routinely shows E & F from 75X on up.
Meade 10" f/10 Schmidt Cassegrain
I purchased this scope specifically for astrophotography back in the mid 1980's. For this purpose, the scope is superb, perhaps today, since a new set of mirrors were installed in the mid 1990's, it's even better than originally! Visually, however, it's a compromise scope. It's compact, but weighs a ton. It isn't much fun to lift a fully accessorized and counter-weighted optical tube and drive assembly to shoulder height in the dark, while trying to finesse the first bolt in the drive base into it's corresponding little slot on the top of the equatorial wedge.
It offers brighter images than an 8", but it's relatively huge central obstruction robs image contrast. Image shift is a problem with many SCT's, this one included, but to compensate on this scope, I've installed a JMI Moto-Focus on the primary focuser, and a motorized 2" JMI NGF-S focuser at the rear cell, so hands-off critical focusing can be accomplished without image shift OR touch-induced telescope vibration. Getting this thing in crisp focus is never a problem, at least mechanically. Getting a crisp image, on the other hand, sometimes can be... The optics take a long time to reach thermal equilibrium. An hour and a half is pretty good. On Arizona nights with rapidly falling temperatures, sometimes it NEVER catches up (this may be even more significant in more northern latitudes). Lots of glass to equilibrate, and optical components not open to the air.
This scope routinely delivers excellent deep space views. The best view of the Whirlpool Galaxy(s) I've ever seen, aside from photos, was delivered with this scope from Peeple's Valley near Yarnell, Arizona, about 90 miles (purely a guess) northwest of Phoenix.
It can deliver surprisingly good planetary images when everything is fully in synch (collimation, stable temperatures, stable atmosphere, transparent skies), but it's more prone to disappoint than please for this kind of work when one or more of the variables are not perfect (which is often).
It's also a great looking telescope. Hang some of it's coiled-wire electrical hardware and hand controllers
on it, and set the legs to full extension and put it in your living room. NO ONE will fail to notice it, and a
whole evening's worth of conversation can originate from it's mere presence!!! Pretty hard to justify it as a piece
of furniture, though, even if it may be the nicest looking non-human thing in the room!
There were no major surprises. For deep sky observing of dim, diffuse objects, the old adage "aperture wins" is demonstrated clearly here. Although the 8" f/6 Newtonian has outstanding optics, when it comes to viewing faint fuzzies, larger aperture still is the deciding factor. The 10" SCT wins hands down. The difference is clearly noticeable, if not dramatic.
For observing open star clusters, and globulars, things gets muddied a bit, because here, contrast and optical quality begin to play more of a part, and the results are less straightforward. For instance, on the Double Cluster, I'd have to call it a tie, with each scope having distinct individual advantages and disadvantages. The SCT's larger aperture brought out a few dimmer stars in this awesome field of diamond dust, and it's additional aperture tended to show off some of the stars' colors better (the orange hued ones really begin to stand out). However, the 8 incher's crisp optics and better contrast, afforded by it's much smaller central obstruction, made the background darker, resulting in a rather more pleasing view, even though it actually contained slightly less detail.
On planetary images, both scopes did surprisingly well. Jupiter's equatorial bands showed a wealth of detail in both scopes. The 10", as seeing came and went, generally delivered slightly more planetary detail, and slightly brighter images at higher magnifications. However, the 8" with it's better contrast & excellent optics, delivered images that were extremely close detail-wise, and actually delivered more satisfying color and what could best be described as better visual separation between low contrast planetary details. Another area where there were notable differences were with Jupiter's four principal moons. They were distinctly imaged as discs in both scopes, but the discs were never quite as crisply shown in the 10" compared to the 8". I could easily make them LARGER in the 10" by driving the magnification on up to 529X, but they never had as "hard" an edge as was shown by the 8" at 292X.
Still, the SCT was a pleasant surprise. I hadn't really done any critical work with it since having it's tarnishing "Multi-Coated Silvered Optics Group" replaced with enhanced aluminum about four years ago. By then, my back had begun to present such problems that the 10" spent much of it's life in it's trunk, because carrying it out from the house and lifting it's fully-accessoried mass to shoulder height, while finessing the first bolt in it's drive base into the corresponding slot in the equatorial wedge was like playing Russian Roulette with my back.
However, once mounted and carefully collimated for these tests, it delivered better planetary images than I ever recall from it. This is possibly because when I sent it to Meade for new coatings, they may have simply removed the optics, and inserted another matched optical set, which just happened to be a little better than the originals. This is purely conjecture on my part, but if true, it would explain the perceived improved performance. The 10" delivered surprisingly good images up to 529X where I stopped, to avoid the added complexity that using Barlows during this test would introduce. At 529X there was plenty of detail, but no obvious new detail was seen that wasn't visible at 362X. I'll want to repeat these tests on the moon where it is much easier to detect subtle differences of this nature, based on known versus observed craterlets in specific areas, but my work schedule hasn't permitted this so far.
The 8" delivered spectacular (given it's deficit in size) images of star clusters & globulars, and delivered excellent planetary images up to 292X (4.8mm Nagler + 1.15X Paracorr). I'm sure it could have gone on up to at least 406X (6mm ortho & 2X Barlow), and probably 507X (4.8mm Nagler & 2X Barlow), simply because I've been there before with it.
If I could only keep one of these two scopes, which one would it be, based on this test?
This would be a very difficult decision to make. I'm primarily a visual deep sky observer. Given that, I'd go
with the 8" if I could make no modifications to either scope. If modifications were allowed, it's close enough
that I might consider putting the 10" on a Losmandy G11 mount, and keeping it. In the real world, I'll probably
keep them both.
I'd guess an Intes Micro MN86 would be slightly better (higher contrast, slightly better optical correction over a larger field) than the 8" f/6, but it would be so close, many folks couldn't tell the difference.
I'm still seriously considering a Maksutov, but this session put a lot of things into better perspective for me (like if I buy a Mak, it'll be because I want one, not because I can justify the improved performance versus the cost. I already have the 8" Newtonian. Spending four to six thousand dollars (with mount) to obtain slightly better performance could only be justified as an Iwannit versus an Ineedit!
In this real world, I'll continue to evaluate the Maksutov idea a little longer. I may yet decide on an MN86, as an alternative to a 7" APO. But I' m leaning more and more toward the TEC 8" f/15.5 Mak Cass.
Although I've always been a proponent of Al Nagler's signature line of eyepieces, I've generally always agreed with the conventional wisdom that for the best planetary definition, orthoscopic eyepieces tend to deliver the best images. And this may be still be the case for most magnification ranges and telescope combinations. But during this testing session, when I got to the top of the magnification range, and was stretching the capability of these particular scopes' optics, the Naglers could always squeeze just a little more performance from the system, even though I was only using a fraction of that huge 82 degree field.
The Naglers continue to impress after all these years. Despite the hoopla, I'm not firmly convinced that the later series necessarily deliver crisper images than the earlier versions, even though they do address certain specific issues. Each Nagler is a wonder unto itself. My only regret is that I let the 11mm get away. Al warned me, but I had other things on my mind at the time, and I let it get away. I'll eventually probably put a "wanted" ad in AstroMart before it's over and pay too much to get a used one.
Final word on fork mounted SCT's:
Fork mounts suck. Ohhh!!! Did I say THAT??? YES!!! Gimme a German equatorial mount anytime!!! If no German equatorial
is available for a given scope, gimme a good altazimuth or Dobson mount. If necessary, I can put an equatorial
table under it! But puhleeeeeze don't give me another fork mount!!! Actually, forks're just fine, if you never
look North. Anyone know where the Whirlpool Galaxy and Double Cluster are??? Or M81 & M82? Or M31 & M39?