On the evening of 31 July, 1998, I helped out at one of Lick Observatory's public programs. I was one of several local amateurs who set up telescopes on the grounds just outside the main building, for public viewing. I brought my Meade 5-inch f/9 ED refractor on my Losmandy G-11 mounting. Other equipment included a 6-inch f/7 Astro-Physics EDF refractor, a Meade 10-inch LX200, and a Meade ETX.
The seeing for the five-inch was good to excellent. Temperatures remained at shirt-sleeve levels, at least on my side of the building, away from the wind. The sky was clear and transparent, so much so that after the Moon had set, the Milky Way was bright and obvious, despite nearby San Jose, which -- alas -- never got close to setting.
I had my equipment going well before the end of twilight, and turned immediately to the first-quarter Moon. The terminator had not long cleared the region of Archimedes, and the rille detail between that great crater and the Apennines was fabulous. I had brought my Rukl Moon atlas -- the large-format one -- and used chart 22 as a reference. Observing at 285x (Vixen Lanthanum 4 mm eyepiece) I could see all of the detail associated with Rimae Archimedes and Rima Bradley. I found the (selenographic) southeastern member of the Rimae Fresnel system, and approximately the southwestern half of the forked rille that completes the system to the northwest.
I am not much of a lunar observer, but the region of Hadley Rille is one of my favorite parts of the Moon. Apollo 15 landed by the eastern extremity of this sinuous, collapsed tunnel made by giant, extinct, Moon gophers (well, that's as good an explanation as any), and well I remember the live video from the Moon's surface: The earlier Apollo landing sites had been relatively flat at the scale of stuff out on the horizon, but this southeastern corner of Palus Putredinis ("Houston, this is Putridity Base..." -- well, not quite) featured some spectacular up-and-down real estate, which awestruck earthbound viewers were privileged to enjoy vicariously from the perspective of a gawking tourist.
On this night at Lick I could again visit and clearly identify many of the sites on another world that I had long ago seen in real time, close up, from a camera on the Moon's surface. The rille itself stood out clearly, all the way from its origin to the southwest, past the Apollo 15 site, then northwest to the boundary of the flat land beyond the mountains. Hadley C was an easy small crater, as were the mountain masses Hadley and Hadley Delta. I looked for the small crater which bridges the rille at the north end of Hadley Delta, but it was beyond the resolution limit of the five-inch. (If memory serves, I have seen it in my Celestron 14.) The great, unstated lie of astronomy, which many of us unconsciously still accept, even today, is that "down here" is somehow different from "out there". Views and memories such as these firmly establish it as a falsehood. It ain't so, it never was, and it never will be.
The disappearance of the Moon behind the dome of the 36-inch refractor forced my attention to other objects. I put in a 12 mm Lanthanum eyepiece and showed the public a handful of Messier objects The 20 mm eye relief of the Lanthanum eyepiece series makes them great for star parties: I focus with my glasses on and tell viewers to leave theirs on, too, and ignore the focus knob. M57 showed a happy donut, M11 was well resolved at the 95x that the eyepiece yielded, and M15 showed its central concentration. At that magnification, Mizar was a wonderful and easy double star, with Alcor wide in the same field. Sky conditions were such that many viewers could separate Mizar from Alcor with the naked eye, providing an interesting visual illustration of just what the telescope was doing for them. With the 4 mm Lanthanum, I demonstrated a lovely and colorful split of epsilon Boo.
Presently I pulled out a new gadget: I recently bought a used Vixen 8-24 mm zoom eyepiece, and was eager to try it out. I had used one in the Orion store in Cupertino before, and at the level of across-the-street views in daylight, it had seemed to be a decent eyepiece -- unlike all the other zoom units I have ever encountered. I was quite curious to see what it would do on astronomical eyepieces in the field. (I should say in passing that the new Tele Vue zoom unit appears identical to the Vixen in every way but cosmetics, though I have only handled the Tele Vue eyepiece, not observed with it.)
The other zoom units I have used have an actual field of view that remains constant as you change magnification. These units generally have a half-way reasonable apparent field of view at their shortest focal length, but as you dial back the magnification, the field of view shrinks in the same proportion, so that at the longest focal length you are looking at the exact same patch of sky, only shrunken in size, often so much so that you might be looking through a toilet paper tube, or almost through the "wrong end" of a telescope or binocular. One thing you might hope for in a zoom eyepiece is a wide field of view at low magnification, for finding things, but the early units do not provide this feature.
The Vixen does. Its apparent field of view is perhaps 55 or 60 degrees at 8 mm focal length, and has contracted by about 15 degrees by the time the focal length has been lengthened to its 24 mm maximum. That means that the actual field of view -- the diameter of the patch of sky in sight -- is approximately twice as large at 24 mm as at 8 mm. A 40 or 45 degree field of view at 24 mm focal length is reasonable for finding things in many amateur-sized telescopes -- even casual use of the finder got things into this field in my five-inch refractor.
How good were the images? I am not sure how many air/glass interfaces the Vixen zoom eyepiece has, but I expect at least six: The eyepiece seems to be a moving-Barlow variant of their fixed-Barlow Lanthanum series. It undoubtedly has more glare, and hence less contrast, than a unit with fewer surfaces, such as an Orthoscopic or Plossl. Yet the coatings were good, and the glare was not especially obvious, even on objects as bright as Jupiter.
Image quality appeared good all the way across the field, at all focal lengths. Star images were round most of the way across, but showed some degradation at the edges. Focus did not change across the field -- the eyepiece either has no field curvature, or happens to match whatever is in the Meade 5-inch. At 8 mm focal length, bright stars showed unremarkable tiny diffraction patterns, with nothing to indicate that the eyepiece viewing them was weird or peculiar. I'd say the eyepiece was working fine, at least at f/9.
The significance of any image defects is minimized because at the focal ratios of most of today's amateur telescopes, eyepieces in the range 8-24 mm are unlikely to be used for high-resolution work. An 8 mm eyepiece would give a magnification that might be called "high" on a classic f/16 refractor, but most of today's amateur telescopes have focal lengths of f/11 or shorter. For my 5-inch f/9 the 8 mm focal length gave 142x, a magnification that is merely loafing, when it comes to things like the Moon, planets and double stars. Even so, I split zeta Aqr at 142x with no trouble.
Using the eyepiece is fun. The focus changes a little as you zoom, not so much as to lose objects from out-of-focus, but enough so you must refocus for critical viewing. The effect is small enough not to be noticed as you twist the knob quickly, changing from the lowest magnification to the highest at the flick of a wrist. With an open cluster or a rich portion of the Milky Way in sight, stars rush toward you in a blur and disappear across the edges of the field. "Quick, Chewie! The jump to lightspeed!" Whee!
Changing the magnification visibly makes clear something we all know but rarely see vividly: The sky appears much less brighter at high magnifications than at low. Varying the focal length from 24 to 8 mm reduces the illumination of the background by nine times. In the conditions that obtained before Moon set at Lick on July 31, in my f/9 refractor, that meant a striking difference between "a lot too bright" and "pretty dark".
One thing a change in background brightness may do is facilitate viewing diffuse objects, and as I had that thought, it occurred to me that at the focal ratios I usually observe with, the range 8-24 mm includes most of the eyepiece focal lengths I use for deep-sky observation. Thoroughly curious, I tried the zoom eyepiece on M8, M20, M31/32, M15, and M52.
Suddenly it was clear that I had an enormous and unexpected win in hand. Each of these objects showed different features and qualities at different magnifications in the range of the zoom, the range of focal lengths at which those features were well seen was narrow -- a few mm, and the difference between "well seen" and "poorly seen" was for the most part great. For example, the obscuring matter in M20 was best seen by a great deal, over a range of eyepiece focal lengths only one or two mm wide, as were the dark lanes in M31. Other focal lengths best showed the emission regions of M20 and M8.
Most people think of a zoom eyepiece as a relatively useless gadget, of which the best that can be said is that it is a rather expensive substitute for two or three conventional eyepieces. What I was finding out was that the Vixen 8-24 mm zoom was usefully substituting for a run of six or eight conventional eyepieces that I not only did not have but did not even suspect I needed, was doing it at about half the cost of separate components, and was taking vastly less time and effort than fumbling in a box to switch eyepieces.
I am not going to make an unqualified recommendation on the basis of a single night's observing, but (1) I will for sure put the Vixen 8-24 mm zoom eyepiece into my eyepiece box, try it out on a great many more deep-sky objects, and report what I find, and (2) I have learned enough to recommend that any serious deep-sky observer seek out an opportunity to play with one of these devices, and see if it is as useful for you as it seems to be for me. The prospect is better views, at less cost, with less time at the eyepiece, and that sounds like a real win. Worries include the prospect that the Vixen zoom eyepiece may not work at shorter focal ratios, and that its merely moderate field width may hamper persons who do not use driven telescopes.
As the evening wore on, Jupiter cleared the trees to the east of the parking lot. The seeing was good enough that I needed more magnification than the zoom provided, so I tried 285x. The view was a little soft -- Jupiter was far enough from the zenith that seeing was a slight problem. I did switch from the Lanthanum 4 mm to a Meade 4 mm Research-Grade Orthoscopic, which not unexpectedly gave slightly noticeably better contrast. I finally settled on a Meade 7 mm Research-Grade Orthoscopic, which provided 163x. I could see several dark bands, with feathery scalloping at their edges, as well as one long white oval. The Great Red Spot -- er, make that the Great Pale Gray Spot -- was coming around the limb as the evening wore on, and I had a nice view of it. The Galilean satellites appeared noticeably different in size.
It was interesting to compare the view of Jupiter in the Meade 5-inch with that in the 155 mm Astro-Physics set up nearby. Its owner was using a 6 mm Zeiss Abbe Orthoscopic when I visited, for a magnification of 181. The Astro-Physics gave the better view, but in my opinion, the Meade was holding its own, allowing for its smaller aperture. It would be fun to compare it with an Astro-Physics 130 mm. As I have said before, the consensus of the two previous owners of the Meade optical tube assembly was that it is one of the better Meade EDs, and they certainly seem to be right. I continue to be impressed with this Meade refractor -- I begin to think it deserves a custom paint job and an appropriate name... I don't think that all of them are nearly as good as mine, however, and I must again point out that Meade's advertising for the ED refractors is shamefully false -- they are fine achromats (at least, mine is), but they are NOT apochromats in any sense of the word.
I looked at Saturn at 163x as well. It was still lower in the poor seeing, but even so, I could see the Cassini division, some banding on the planet, and perhaps a hint of the Crepe ring, at the inside edges of the ansae of the ring system.
I only looked once through the 10-inch LX200. Its owner had put in an OIII filter for a lovely view of the western arc of the Veil Nebula, at 98x. I tried my Meade on the Veil, using the 8-24 mm zoom at its lowest magnification of 48x. I did not put in a filter, so the view I had was not nearly as good, but I could find both the eastern and western arcs.
At the end of the evening, we stragglers got to look through the 36-inch refractor at some galaxies, to see if any late-summer examples of these objects were suitable for public viewing. We observed at 316x, with a 55 mm Tele Vue Plossl. NGC 6946 was a pretty face-on spiral, showing nuclear concentration and disc, but probably not whiz-bang enough for laypersons. NGC 7457 was similar -- it had a fainter companion very nearby, evidently not bright enough to make the NGC. The win was NGC 7331, which to my eye showed obvious spiral detail, and at least three nearby companions, though for want of scale and orientation I could not positively identify any of them. I suspect that some were too faint for the NGC.
Three of us were convoying back down the Mount Hamilton road at 0300, and passed a car by the side of the road, with someone standing beside it and waving. The car was a low-rider hot rod, and the waver was a slender, lightly bearded young man wearing a cowboy hat. Mount Hamilton Road at night is lonely, dark, and fearful, and I am sure that if none of us would have stopped if we had been on our own. But in convoy, we halted, and were glad we did. The car -- an immaculate, beautiful, and sanitary modification of a '66 Chevy Nova, in a color that reminded me of Refractor Red, had a broken fan belt, and its occupants -- a charming couple in their twenties -- had been stranded for hours because no one would stop to help. They had been country-western dancing in Sunnyvale, and were on their way to a friend's house off Mount Hamilton Road, when the breakdown happened. The driver had had a little experience with a friend's large Newtonian, so we had something to talk about after we ferried them to a call box and were waiting for the AAA truck. (Only one of us had a cellular 'phone, and its batteries needed charging.)
Between playing good samaritan and the obligatory stop for food, I didn't get to bed till the sun was rising. It had been an uncommonly good night -- I observed the Moon, planets, double stars, open and globular clusters, bright, dark and planetary nebulae, galaxies, and a couple of sporadic meteors, I had used a classic Great Refractor, and I had performed useful public service in the interest of astronomy. I wish you all nights that are as fun and as satisfying, and I hope you get to sleep as late as I did on the mornings after.