by Jay Reynolds Freeman
I was at Lick Observatory Friday night, June 15, 2001, helping with a public event. I was one of the folks assigned to provide an extra telescope. I brought my 10-inch Astro-Physics Maksutov-Cassegrain.
Mars was the target of the evening. It was too far south for the 36-inch without using an observing ladder, which is rather a pain for long lines, but most people knew about the opposition and wanted to see it. Fortunately, seeing cooperated. My first clue that it was a good night was shortly after polar alignment, when I viewed Polaris through the main optics and encountered crisp, almost steady diffraction rings at 464x. Mars wasn't as high, but even so, seeing was sufficient to warrant 464x (8 mm Brandon) and 618x (6 mm Pentax SMC-ED orthoscopic). There were intervals many seconds long, particularly later in the evening when Mars was higher, when I could detect no seeing jitter with either of these magnifications.
Sometimes I used a Wratten 23A filter (red) ahead of the eyepiece, not because it was necessarily the best one, but because it was what I happened to have. It improved contrast of the dark shadowy markings against the brighter, pinkish-orange portions of the planet, but I am not convinced that I could see anything with the filter that I couldn't see without it.
I am not an artist, so I did not make drawings. Perhaps the best way to describe the level of detail visible is to say that near the center of the planet's disc, most of the albedo features shown in the Mars map that accompanied the article on the opposition in the June, 2001, issue of Sky & Telescope, were visible at the eyepiece. One exception -- something I could *not* see -- was the notched protrusion on the west side of Syrtis Major -- I could see the protrusion but could not tell it was notched. On the other hand, on the opposite side of Syrtis Major, the small protrusion of Moeris Lacus was visible. Both polar hoods were seen. Hellas was defined, but not nearly as bright as it has been in the past two oppositions.
As the planet rotated, we had a nice view of everything from the east end of Mare Cimmerium, through Syrtis Major and a bit beyond. It was fun showing members of the public a world-class view of Mars, and coming up with ways to describe what they were seeing, and to tell them how to use a high-magnification eyepiece successfully.
I likened the (north-at-the-top, reversed) view to the view of the thumb and first two outstretched fingers of my right hand, seen palm toward the viewer with the thumb pointing up. The thumb was Syrtis Major, which was coming around the right side of the planet at the time, and the two fingers were Mare Cimmerium and Mare Tyrrhenum.
The key to using the eyepiece was to focus it with my glasses on (I wear glasses for distant vision), then tell viewers to do whatever was necessary to get their own best distant vision, locate Mars in the field of view, and BACK OFF from the eyepiece -- so as not to touch and jiggle it -- while keeping the planet centered in the portion of the field still visible. Even with a 6 mm orthoscopic, one could observe the planet with as much as 35 mm between eyepiece and eye. That would not allow seeing the entire field of view, of course, but Mars wasn't as large as the entire field of view.
Some people preferred 464x, some 618x. The tradeoff between reduced surface brightness and larger area of individual features is subtle, particularly for low-contrast details. I felt that 464x produced a view that was more often more aesthetic, but that 618x gave me the best chance of seeing all the detail that was there, particularly if the seeing went clear when my eye was not directed squarely at some interesting feature that was only just then visible.
After the public had left, we volunteers got a real treat -- a view of Mars through the 36-inch refractor. The telescope was loafing; the eyepiece was a 35 mm Panoptic, yielding 496x. Unhappily, it was more compromised by seeing than were the smaller, amateur instruments, and the glare of chromatic aberration noticeably degraded contrast on the planet's disc. Proper use of this instrument on the planets would require excellent luck on seeing and careful choice of filters. It would be particularly interesting to see how well it worked with narrow bandpass filters, such as were not available during its heyday.
Under the circumstances, it is perhaps not surprising that some amateurs present believed the 10-inch Astro-Physics Maksutov-Cassegrain offered a better view of Mars than the 36-inch refractor. I am not quite ready to say so myself, at least, not entirely: I thought the view of brightness variations -- what might be called "texture" -- in the darker areas of the planet was better in the 36-inch than in the AP-10, but that the AP-10 had perhaps slightly the edge on small, low-contrast detail. Good filters and better seeing would be required for a more interesting comparison, but I think that all present were much impressed with the performance of the Mak-Cass.