by Jay Reynolds Freeman
By coincidence, I was observing with my Astro-Physics 10-inch Maksutov-Cassegrain, whose name is Gillian, six months to the day after its first light. Besides the calendar coincidence, there were two other events of note with the AP-10 that evening. I completed its Messier survey, and I logged its thousandth observation.
I posted a long AP-10 report during the month after I got it, and will restate its conclusions to start this update. (For the original report, send private EMail to freeman@netcom.com, and ask for one.)
Those conclusions all still stand, except -- as I am about to discuss -- hot spells in California this spring required me to make more use of the telescope's thermal-control features. The summary of the original report read "For persons with ten thousand dollars to spend on an OTA, an Astro-Physics 10-inch Maksutov-Cassegrain is certainly one to consider," and I still think that is the case.
I used the telescope seven or eight times in the month after I got it, then once or twice more in the rest of the first quarter of 2001. It sat in its case till Mars started getting large, but now, with the current Mars opposition approximately half over, I have used it five times more, with the primary mission of viewing the tawny planet.
A thousand observations in fifteen setups is a lot -- nearly 70 each time out. Only my Celestron 14, Harvey, do I use more intensively. The AP-10 approaches the C-14 in deep-sky capability, and gets close enough to do deep-sky work with it and not feel too compromised by the lack of Harvey's larger aperture. Thus even for a few targets that require the superb resolution of Astro-Physics optics, I can bring the AP-10, and spend the rest of the evening on faint fuzzies. My main program for the last year or two has been working Millennium Star Atlas, page by page, north of 39 degrees south declination, trying to see all the deep-sky objects plotted. The AP-10 can show me most of them.
I encountered very good seeing on several nights. It was best near the zenith, unfortunately, while the new interesting target since winter -- Mars -- is well down in the south. Notwithstanding, the telescope delivers fine images of relatively tight double stars, such as eta Corona Borealis. In less than perfect seeing, partly because of angle off the zenith and partly because it was still early in the year, I split both Sirius and Procyon.
Mars has been a wonderful sight -- I have posted several separate reports on Martian observations with the AP-10. I can see nearly all the detail on the Mars map in the May, 2001, issue of Sky & Telescope, near the center of the planet's disc. For these observations, I have used of 464x (8 mm Brandon) and 618x (6 mm Pentax SMC-ED orthoscopic), sometimes with a Wratten 23A (light red) filter. I also spotted Deimos and Phobos, at greatest elongation, by putting Mars just outside the field stop of a high-magnification eyepiece.
The Messier survey was delightful. I habitually used a Vixen Lanthanum 8-24 mm Zoom eyepiece, which permitted easy finding at the low end of its magnification range (155x), followed by a twist of the ring to make the stars rush out ("Quick, Chewie, the jump to light speed!") to see how it looks at 464x. Globular clusters were particularly nice with this approach; they all but sparkled. If memory serves, all Messier globulars but M54 showed at least granularity at 464x.
The AP-10 has two interchangeable baffle discs that fasten to the center of the corrector, to block light from the field. The larger one widens the 23 percent obstruction to over 30 percent, to enlarge the baffled area from about half an inch to the width of a two-inch eyepiece barrel. The extra baffling reduces contrast in high-magnification views, but you only put in the big baffle for a wide field, not for high magnification. In any case, I rarely use the wide baffle. There are few objects I look at that are so wide as to spill over the field stop in a fat eyepiece. By habit, I center things, and that leaves what I want to see mostly in the area well baffled by the small disc. If I look hard, I can sometimes detect the extra skyglow outside the half-inch area, and when there is a bright star near there is sometimes a lot of glare. I would use the large baffle for wide-field imaging.
The California sun provided a chance to test the telescope's high-tech thermal control. Several times I reached the observing site near sunset, with the telescope having baked in a hot car for much of the day. On such occasions, I put the optical tube on the mount as soon as I can, remove the back cap, and set the muffin fans to "hurricane" mode while I complete setup. Five or ten minutes later, the back of the quartz primary is cool to the touch. Seeing shortly after dusk then appears not affected by thermal effects, at least, not that I can see.
Once I had the telescope side by side with a late-model AP 180 mm EDT refractor, looking at Mars. The seeing allowed an excellent view with both, but not a critical comparison on fine, low-contrast detail. Both I and the AP-180 owner noticed that at the same magnification (about 450x), the brightness difference between the two telescopes was very noticeable. With fine, low-contrast detail, it does help to have a bright image, so that is an advantage for the 10. We also noticed that in the seeing that prevailed, the 10 appeared to give up nothing to the 180 in contrast of fine detail. That's good, because it shouldn't -- indeed, in excellent seeing, I would expect the 10 to do slightly better than the 180 for such features. Yet we will have to wait for a better night to see if it does. (The actual seeing that night was such that we could just get a hint that Meridiani Sinus might be notched.)
We also tried the 180 owner's Zeiss bino-viewer with the 10. It worked fine, or so my friend said, and so it seemed to me. Yet I have little experience with bino-viewers -- I don't like them -- so cannot pass critical judgement on that configuration.
The telescope is noticeably easier to set up than either my C-14 or my 1987-vintage, pre-ED-glass Astro-Physics 6-inch f/8 refractor. I keep using the C-14, because of its greater aperture, but I have not been tempted to set up the 6-inch since I got the 10. (No, the 6-inch is not for sale. Down! Down, I say!) Part of the ease stems from the rope handles I added to the top of the tube, front and rear. Otherwise, it might be more than my nerves could stand to move the OTA around.
The only down side to the AP-10 showed up one night I took it to Lick Observatory, to help relieve long lines at the big instruments on a public night. The big Maksutov-Cassegrain was so popular that I myself scarcely got to look through it. I guess I shall have to live with it. I'm certainly not going to trade it in on a lesser telescope.