by Jay Freeman
My new Astro-Physics 10-inch Maksutov-Cassegrain had first light Saturday, 16 December, 2000, at Henry Coe State Park, not far southeast of Lick Observatory. It was a frustrating night -- seeing mostly so-so, transparency mostly poor, scattered to broken cloud intermittently crossing the sky. At no time that evening did I see anything resembling an Airy disc surrounded by diffraction rings, and I don't believe anyone using any of the other telescopes present did, either. On the other hand, things could have been worse -- there were twenty thousand dollars worth of new stuff there, which should have invoked the curse of the new telescope in massive force. We were making jokes about using kayaks to paddle down the hill and get home.
I expect to use the AP-10 intensively during the next few weeks, weather permitting, and I will continue to report on its performance. Yet plenty of people are waiting to hear how it did, so I am not going to wait for razor-sharp seeing to post. In central California winter, that's likely a long wait.
The OTA case fit sidewise in my van with a little wiggling, and made it all the way to the site without shucking around too much. I arrived while the Sun was still well up. That was part of the plan: I had foregone an opportunity to use the telescope the night before, because I wanted my first set-up to be when I could see what I was doing.
I configured my Losmandy G-11 with three 21-pound counterweights. I suspected I only needed two, but did not wish to shown wrong by having the OTA do a vertical reverse from being out of balance.
The key part of setup was dovetail alignment. Those of you who have read my postings about Harvey, my Celestron 14, may recall that I have spent moderate effort making special components, so I do not have to do a precision dovetail alignment of 52 pounds at shoulder height. The AP OTA was lighter and smaller, but was a dovetail alignment reasonable?
I set the latitude adjustment to 20 north, as low as I could get it without the counterweights hitting the tripod. With the dovetail clamp parallel to the polar axis, I would be sliding the dovetail plate up a 20 degree slope as I installed the OTA from the south. I could have gotten a shallower slope with the clamp pointed east and west, but at the expense of a rotating polar axis messing things up.
I cleared a spot on the floor of the van in case I needed to set the OTA down. I made sure the safety screw on the north end of the plate was out, then lifted the OTA by my new rope handles -- they worked great! -- and carried it around to the G-11. Installation was smooth and easy, and I was much relieved as I tightened the dovetail clamp and re-installed the safety screw. This telescope will not require any special hardware for me to set it up. (Your mileage may vary -- I do push-ups regularly.) Then I elevated the polar axis to the latitude.
I paused to remove the rear dust cover and let other people inspect the cell and focusing mechanism, then installed my new MaxBrite star diagonal, finder, and dew cap. Relative humidity was in the mid 40 percents, and temperature was 15 C, but I wrapped an anti-dew heater around the dew cap, just in case. Yet I did not need it that evening.
Both the front dust cap and the dewcap were tight fits, even with the latter's setscrew backed way out -- I had to tug some to get them off. Too tight is better than too loose, but I have often wished there were a reasonable way to make the tightness of such items adjustable.
The telescope indeed required only two 21-pound counterweights, so the mounted weight was perhaps 35 pounds less than for my C-14. The longitudinal balance point of the tube was much further forward than for a Schmidt-Cassegrain, approximately half way from primary to corrector. Thus variation in eyepiece height as the telescope looks at different parts of the sky is greater than for my C-14. With the telescoping legs on the Losmandy at full length, the eyepiece was convenient for most of the sky, but it required scooting way low in my observer's chair to view the zenith, and using the finder then required much pretzeling of my spine. Perhaps I should put another finder on the front end of the tube, just for use in such circumstances.
The telescope had sat in the cool car most of the day, and I set up well before sunset, and it did not seem likely that the temperature was going to drop much, so I felt no need to use the muffin fans to cool the mirror, or even to leave the rear dust cap off for long. My guess about temperature was right -- it dipped only to 10 C during the evening.
I aligned my finder with a tree on a nearby hill. The Maksutov's optics certainly worked, the belt-drive focuser felt smooth and solid, without a hint of backlash, and there was no image shift while focusing. Images appeared good all across the field, and indeed, I did not notice any off-axis aberrations of any kind the whole night long.
First light on a celestial object was a view of Jupiter at 309x (12 mm Brandon). I spotted the giant planet while the sky was still blue, and turned to it immediately, hoping that seeing would be very good at dusk. No luck, the image was turbulent. I could see several belts, and even some scalloping in them, but little detail. Other telescopes confirmed the problem was seeing, not turbulence in the tube. Saturn was similarly poor. I looked at Venus, whose half illuminated disc was spectacularly brilliant, utterly color free, and seemed to show a hint of shading variation across its surface, then decided to give up on planets for a while. But keep reading, I got back to them later.
I tried a few stars. There was no trace of an in-focus Airy disc, just swirling glare, but I could see enough out of focus to verify that collimation was okay, and what is more, what I could see looked the same inside and outside focus -- scarcely a critical measure of quality with so much turbulence, but encouraging nonetheless.
So I switched to a Vixen Lanthanum 8-24 mm zoom eyepiece to hunt bright deep-sky stuff. I logged over 70 objects during the evening, so I will only give highlights here. As I began, it still wasn't quite dark, and I had the fun of looking at the ring nebula at 155x against a sky background that was distinctly pale blue. It was its usual oval shape, softer at the points of the oval than elsewhere. I could not detect the slightly ruddy periphery that I have occasionally seen with my C-14, even later, when the sky was dark. I ran magnification up with the zoom -- if the seeing had steadied I would have put in a better eyepiece and tried for the central star -- but had no luck on seeing.
For the next few hours, I chased sucker holes or peered through thin cloud at deep-sky objects, mostly using the zoom eyepiece at 155x (24 mm focal length), but occasionally with a higher magnification. M15 was notably higher up than the gas giants had been at sunset, and at 464x -- 8 mm on the zoom eyepiece -- it was resolved almost all the way across, with only a tight core that was merely granular. M2 was similar, though not as well resolved, perhaps because it was nearer the horizon.
h and chi Persei were pretty examples of open clusters, both blown more than wide open, showing numerous colored stars. The Auriga Messier open clusters were wide open and looked very different from one another. M35 plus its smaller neighbors, NGC 2158 and IC 2157, provided an interesting contrast in size and compactness of open cluster.
Central Orion has plenty to test a telescope with. I looked at M42 and M43 several times, both with the zoom eyepiece and with my 40 mm Vernonscope Erfle, which gave 93x. M42 showed a pale green core around the trapezium, shading into dark reddish-purple tones in the "wings" of the nebula. There was not as much textured detail in the nebula as I have seen with better seeing, and a glance at the Trapezium showed why -- with Orion not far above the horizon, often, the edges of the images of its brightest four stars touched. The seeing was better at times, but even knowing where to look, I could not see stars E and F.
The late autumn sky also has some bright galaxies. I only had an unremarkable view of M74 and M77, through thin cloud, but M31 was pretty even through the same, showing dark lanes at 155x, and traceable out as far as star cloud NGC 206. M32 and M110 seemed to have different textures as well as different surface brightnesses. The view of M33 through cloud at 155x was not impressive -- all I could see was the central part of the galaxy, but a later view, at 93x through a break, showed the stretched-out S shape of its spiral arms unmistakably.
After I had looked at forty or fifty objects, I was beginning to be a little tired and thought it must be late. But no -- it was winter, and I had started observing at dusk. It was 8 PM. I took a coffee break and offered the telescope to some friends, who are experienced planetary observers, for a while. They promptly turned to Jupiter and Saturn and started playing with eyepieces. Seeing had improved a bit, and the spot formerly known as "Great Red" had come into view. They and a third observer, who had a late-model AP 155 EDFS set up ten meters away, took turns looking at the large planets. The consensus seemed to be that though the night was not first-rate, the AP-10 was showing more detail than both smaller telescopes and larger ones. (The larger ones were fast Dobson-mounted Newtonians, and I did not record whether the smaller one included the AP 155.) That is a very positive and strong statement. If true, it may indicate a combination of two things; first, that the telescope was of a useful size for the seeing that prevailed -- more aperture would have resulted in taking a much worse hit from poor seeing -- and second, that the telescope itself was not doing much on its own to ruin the image, that is, that its optics were very fine. All this is as I had hoped when I ordered it.
A wide sucker hole crossed Auriga and Taurus, so I tried a few objects there from my serious deep-sky list. I only looked at one faint galaxy, UGC 3374, but at 93x, I could see it. I also spotted the extremely faint planetary nebula, IC 2120 -- I could only suspect it at 93x, even with an Orion UltraBlock light-pollution filter, but at about 300x, with the zoom eyepiece, I could hold it without the filter. If the telescope can pull in these demanding objects, it can probably do most deep-sky work in my current C-14 program. I don't think it is quite as good as the C-14 for deep-sky -- a factor of two in collecting area gives the larger instrument an enormous edge -- but Harvey's coatings are twenty years old, and were never as high-tech as the AP-10's, so the difference is closer than you might expect, and my current deep-sky program doesn't usually push the C-14 to its limits.
I was still using the small central baffle, whose diameter matches the aluminized spot, but when I tried another deep-sky object in Auriga, diffuse nebula Sharpless 2-234, I found an annoying flare of light -- most likely from nearby Capella -- overlying part of the field, so I switched to the second, larger baffle, that came with the telescope. The baffles screw on to a threaded stud that protrudes skyward from the center of the corrector plate -- I did not look closely at how it attaches. Unfastening the small baffle was no problem, but installing the larger one was nerve-wracking. It was reluctant to thread on cleanly, and I certainly did not want to cross-thread it. I finally got it on, but it would have helped if there were some means to line it up squarely before engaging the threads. Perhaps the outer tip of the stud could be turned down so that it slipped inside the inner diameter of the female threads in the baffle, to guide the threaded portion into place? Anyhow, with the larger baffle in place, the flare went away, and I could see part of Sh 2-234 with no problem. The field of view was nice and dark -- I would say the baffling was excellent.
As the earth rotated, objects I had looked at before became better placed. I returned to Orion, and explored further. I had a nice view of NGC 2023 and 2024, and an unaesthetic but nonetheless convincing look at the Horsehead Nebula, all at 93x with no filter. Then I turned again to the Trapezium and put in my 8 mm Brandon. Seeing quality varied, and after some minutes waiting and tweaking the focus, I did have solid views of stars E and F. That is not much to cheer about -- I have seen six Trapezium stars with my 55 mm Vixen fluorite refractor -- but any bright star with a close, faint companion is a sensitive indicator of poor seeing or scattering in the optics, for the slightest smear of the bright star will wipe out the faint one.
Feeling optimistic, I tried Sirius, but no luck. I did see the Pup in 1999, with the C-14, and in seeing that was not perfect, so it is possible I could find it in the AP-10 on a good night.
I tried Jupiter and Saturn again, using the zoom eyepiece to pick the best magnification. They were just about transiting. I ended up with about 250x on Jupiter, but the Great Pink Spot was rotating out of view, and I am not a particularly experienced Jovian observer, so I am not sure what was special and what was not about what I saw. I did notice that the Galilean satellites were clearly small worlds of different angular sizes, though. And I switched to Saturn.
A little to my surprise, I found myself dialing the eyepiece to its shortest focal length, 8 mm, so I put in the 8 mm Brandon instead. At 464x, in moments of better seeing (but the seeing was far from perfect, even at best) the Cassini Division appeared crisply defined, changing abruptly from dark to bright at its boundaries, not the fuzzy-edged vague black smear of smaller apertures. The Crepe Ring was easy, like gauze. The B ring did not have constant brightness across its width. Within the A ring, the broad brightness minimum half way from its outer periphery to the outer edge of the Cassini Division, was easy, and I had occasional glimpses of a narrower dark feature between that minimum and the outer edge of the A ring, rather closer to the outer edge. Both these A-ring features have had the name "Encke" applied to them, but the nomenclature of the details of Saturn's rings is so confusing I have given up using it. I looked for but did not see "spokes" in the rings.
On the disc, the dark band in the north temperate zone appeared narrower than usual, and even at 464x it showed a pronounced brown color. I also had a sense that the visible polar area of the disc was darker than most of the rest of it, though not as dark as the band.
The view of Saturn was startlingly good considering the so-so seeing, and also considering that I was still using the large, not-quite one-third-diameter, secondary baffle. I have had views approximately as good in my 1987 six-inch Astro-Physics f/8 triplet refractor, and in my C-14, but only on nights of vastly better seeing, for both telescopes.
I took the telescope down at Moon rise -- thickening cloud precluded doing anything else while waiting for Luna to get high enough to be a good target. Everything came apart as easily as it had gone together, and shortly the Mak-Cassegrain was stowed in my van for the ride home.
A fair summary of the night's experience would be the following:
All well and good, but what a lot of you probably want to know is, is it worth ten thousand dollars? There are two parts to the answer.
First, no telescope is worth ten thousand dollars if you don't have ten thousand dollars to spend on a telescope, and many do not. Persons with a lower budget limit, or whose concern is performance per dollar, should not consider this telescope.
Second, for you who do have ten thousand dollars for a telescope, I can say with some confidence that the AP-10 is a viable choice. I did not order it on a whim, or out of pocket money. I was ready to spend a lot on new equipment, and I thought much about large Dobsons, possibly with tracking, as well as about collections of fancy accessories. Yet I ordered an AP-10. The one night I have had it out demonstrates that it almost certainly delivers more resolution on low-contrast detail than any other telescope I own, and that it provides enough capability for much of the deep-sky work I like do, all in a package that is easy to set up and convenient to use. That is a combination worth having. You should all hope that Astro-Physics produces some more of these, because I doubt I am going to sell you mine.
There is one more thing. I never have gone out of my way to name my telescopes, but many of them have nevertheless told me what their names are, or ought to be, and so it is with this one. I am not absolutely sure, but I think she is "Gillian". Persons familiar with magical co-stars of Jimmy Stewart may be able to figure out why.
| Next |
|---|
| Part I |
| Part II |
| Part III |
| Part IV |