Just about a year ago I bought my first APO as a 70th birthday present to myself. I did it for a variety of reasons, including simply scratching an itch. I knew I'd always be dreaming of buying an APO if I didn't actually do so.
My choice was an AT80EDT on the grounds that I wanted the scope to be clearly superior to my very first -- the Tele Vue Ranger -- in every way except price and portability. Actually, in inflation-adjusted dollars, the AT80EDT is considerably cheaper than the Ranger was when I bought it 28 years ago -- which makes its far superior optical and mechanical quality all the more impressive. As a cute plus, the AT80EDT has exactly the same focal length as the Ranger (480 mm), meaning that with any given eyepiece it delivers the same magnification, but with a bit more aperture to back it up, and much less false color on bright objects.
On the other hand, the AT80EDT is nowhere close to the Ranger in terms of portability. It's small enough, but weighs more than twice as much, and requires a much beefier mount. Which may be a good thing, because I finally splurged for a Bogen 3046 tripod, which works far better than lighter tripods do for the Ranger. Eventually I think I will want a Go To mount for the AT80EDT -- or more likely two, a lightweight alt-az Go To for visual observing, and a serious EQ mount for imaging. But the Bogen 3046 is just about ideal for wide-field browsing, and still perfectly adequate at high power.
All this raises the question: what's an APO good for? Part of the answer is that APOs are ideal for attaching cameras and other instruments -- but I haven't gotten around to doing that yet. For the moment, I'm thinking strictly in terms of visual observing.
From one point of view, APOs are good for everything. From a more cynical point of view, they're good for nothing, due to their ridiculously small apertures. (I'm basically a Dob kinda guy.) With the hindsight of a year of (admittedly rather limited) experience, I'd say that they excel at two things: providing truly expansive low-power, wide-field views, and providing great views of bright stars and multiple-star systems -- within the limits of their apertures. Oh yes, and they're also great for viewing Venus. Not so great on the other planets, due to their tiny apertures, but since there's hardly any detail to see on Venus, small aperture isn't much of a limitation. Likewise for stars -- they show precisely zero detail in any telescope, no matter how big. But if you want to see diffraction rings, you can't do better than a small APO.
I spent a very enjoyable few hours a couple of nights ago on my first serious deep-sky session with the AT80EDT -- the kind where I actually record my observations, and look for objects other than the two or three hundred that I more or less know by heart. I tried all three of my two-inch eyepieces with the telescope, the 27-mm Panoptic, 30-mm UFF, and 40-mm Orion Optiluxe. I specially bought the 30-mm UFF as a companion for the scope, and indeed it proved to be the best of the lot for my purposes. The Optiluxe is a great finder eyepiece, but 12X is ridiculously low magnification for an 80-mm scope, especially given that my pupils now open only to 4.5 mm. The 27-mm Panoptic shows significantly fainter star and finer details than the 30-mm UFF, but at the cost of a much smaller true field of view. The difference in TFOV is much bigger than the numbers suggest, because I can see very nearly the entire field of the UFF in a glance, even while wearing glasses, whereas I have to crane my neck at weird angles to see the Panoptic's field stop.
I also viewed (or attempted) all the same targets with my Oberwerk 15x70 Deluxe binoculars. It was quite an instructive comparison, because those binos theoretically have almost exactly the same true field of view as the scope with the 30-mm eyepiece, slightly over 4 degrees. But again, I absolutely cannot see the whole field of view of the binoculars wearing glasses, and my astigmatism is really obtrusive at wide-open exit pupils when I don't wear my glasses. Also, it's much easier to fit the scope with filters, which mattered for some of my targets, notably the Rosette Nebula.
As is my custom, I was using the binoculars hand-held, so it's not surprising that I could see much finer detail with the scope. On the flip side, large, none-too-bright objects like M46 definitely had more presence in the binoculars. That's not surprising given that the binoculars two 70-mm objectives gather far more light than the scope's 80-mm objectives. And as we all know, two eyes really are better than one.
Overall, though, I'd have to say that I enjoyed wide-field observing a lot more in the scope than in the binoculars, due primarily to the 90-degree viewing angle. Oh, by the way, I was using an Amici prism. I have no desire to return to a conventional star diagonal, except maybe for splitting close double stars. I despise mirror-imaged views, especially at low power where the correlation between the naked-eye view and the view through the scope is so obvious.
For close-up views I used my Baader Hyperion 8-24 zoom, which I find complements the scope beautifully. I was observing the tail end of the winter Milky Way, in Monoceros, Canis Major, Puppis, and Hydra, which contains many bright clusters and nebulae that are well suited to small apertures. Even so, I kept thinking "gosh, I sure wish I had just a little more aperture." Any way you slice it, 80 mm isn't much. Nor is 100 mm, for that matter.
I ended the session just before the Moon rose by observing NGC 2903, the first of the great spring galaxies. It was nice enough, and perhaps even exhibited a hint of its bar structure. But I think I will put away the little refractor for galaxy season, and return to my 7-inch and 12.5-inch Dobs. Which, when all is said and done, are much more versatile instruments as far as visual observing is concerned. And certainly far superior for galaxies.
Edited by Tony Flanders, 20 March 2025 - 08:18 PM.