I’ve tried a lot of telescopes since I got back into astronomy as an adult after the harrowing weeks around September 11th. In part I am on a search, familiar to a subgroup of amatuer astronomers, for the perfect observing setup. This group pursues its quarry one of two ways: either buying and selling commercial telescopes, or making their own.
I’ve done a little bit of both. I’ve made quite a few telescopes, although I have never been as hard-core as some in the ATM (Amatuer Telescope Maker) community, those who grind their own mirrors and make everything from scratch. I’ve mostly built newtonian reflectors, and those from parts generally available over the shelf. My biggest endeavor was building a telescope from a kit by dobstuff.com, which I wrote up for the magazine Astronomy Technology Today. (Dennis has a pdf of this up on dobstuff.com, you can view it here.)
But recently I was talking to a retired college professor named Larry from Salt Lake City, and he asked me about some of my favorite telescopes from those I’ve used over my years in the hobby. Which got me thinking…what would my short list be? Which are the ones that gave me unforgettable views. And what have a I learned from trying so many telescope, and building a few?
So here’s a list of my favorites.
Tasco was an American company that imported Japanese-made telescopes for years. The 10TE was sold from the late 1950s into the 1970s, according to John Siple, who writes about classic telescopes for the Rosette Gazette, the newsletter of Portland’s Rose City Astronomers. I got mine from a gentleman in Arizona, I believe, with the idea of spending a winter observing double stars.
The 10TE is the 76.2mm (3-inch) refractor of the Fraunhaufer doublet design, with a focal ratio of 15.7. It was a long scope! And even longer than it looks, since it was designed to have a very long sliding drawtube. Mine only had a holder for .967″ eyepieces, which is an old and outdated standard. I didn’t know it at the time, but Vixen makes an eyepiece holder that fits modern 1.25″ eyepieces that fits this old focuser! The Japanese must love their traditions. But, not knowing this, I took the focuser to a local machinist. It was my first time in a machine shop, and I was fascinated. We drew up a collar that would attach to the drawtube and lock down, and provide a standard opening. I think it cost around $40 to make. I was proud of my modification.
I mounted the scope on a wonderful mount, a Losmandy GM-8. I will do a post on favorite mounts some time, too.
That scope, which was the subject of many amatuer astronomer’s dreams in the 60s and 70s, is pretty modest by modern standards. But I have to say it gave me some of the most indelible views ever. In particular, I remember an amazing view of the Plaiedes, a nearby open cluster visible to the naked eye. It was the first time I glimpsed, or though I glimpsed, the faint nebulosity that shroud those stars. I also cannot forget the view of the globular cluster M13, a faint patch with a spidery overlay of stars shimmering in and out of resolution.
I sold that scope to get something with more aperture after my winter of double star observing. I replaced it with another unforgettable classic scope, the Meade 628 reflector.
I don’t have a photo of the Meade. The scope kept morphing, anyway, as I “improved” it. The Meade was a 6″ fl8 newtonian reflector manufactured in California in the late 1970s/early 1980s. I still think a 6″ f/8 reflector is the best beginning instrument a new astronomer can get, and I prefer it to the larger 8″ f6. At f8, the abberations of a newtonian reflector (namely coma) are minimal, and the secondary mirror is small enough to not make a very noticable impact on the contrast of the image.
I had a lot of good times with that Meade. I had it on the Losmandy GM-8, which allowed my to track objects, but as anyone who has observed with a an equatorially-mounted reflector will tell you, the eyepiece ends up in some odd positions and the tube needs to be rotated in the rings often. I built a simple dobsonian mount kit I bought online, and used that for quite a while.
I did public outreach at my first star party with that scope. And it accompanied me to quite a few local star festivals and at least two Black Forest Star Parties at Cherry Springs State Park in Pennsylvania. Most of the time I would set up my little scope next to my friend Peter’s monster 17″ newtonian. And I learned a lesson from this. Peter would hunt down obscure little galaxies and I would follow him. Much of the time whatever he saw, I could see in the 6″ scope. Usually it was a matter of knowing where to look. And perhaps younger, more sensitive eyes than I have now.
One of the drawbacks of the newtonian design is that the secondary mirror and the vanes that hold it obstruct some of the light path. The light lost is minimal, but the vanes scatter light, giving stars and planets a thin, cross-shaped overlay. It’s not a big deal, in fact some astrophotographers add these diffraction spikes to their photos for aesthetic reasons. I don’t really like them, however, though I liked the other attributes of the newtonian, namely cost per inch of aperture (generally much cheaper than refractors with multiple lenses) and the fact that they don’t suffer from chromatic abberation, or false color.
Enter Dan McShane’s off-axis reflectors. These are somewhat exotic beasts. I’ve only seen one other at a star party, a massive 9″ one. An off-axis reflector is best thought of as a slice of a larger newtonian, allowing the secondary mirror to be off to the side so it does not intrude on the light path. Here’s the OA5.5’s secondary, mounted on the side of the tube just under the focuser:
I actually met the optician who made the mirrors for the DGM scopes, Rod Dodgen in Flagstaff, Arizona, and he explained the process. He basically makes a large, short focal ratio mirror, say 14″ across. He then uses a big hole saw to “core” four round sections from the parent mirror. I actually still have a 6″ f7.5 set of optics from Rod that I hope to turn into a lightweight travel telescope soon.
I really enjoyed hte OA5.5. It took some getting used to. In particular, collimating (aligning the optics) was a new experience. It had to be done on a star, and carefully. And the optical theory at work was interesting too, which the residual coma appearing like astigmatism, though when the scope was well-collimated, this was minimal. What it afforded was extremely high-constrast views of planets and deep sky objects, in part because of the unobstructed design, and in part because Rod Dodgen’s is a perfectionist of an optician who grinds extremely accurate, smooth mirrors to begin with.
One of the downsides of this scope was the tube length. I don’t recall the focal length, but I believe it was around f10, which means the light path was about 55 inches long. It was just long enough to be a bit tricky to fit into hte back seat of my 1989 Honda.
I’ll continue my review of past telscope loves in the next post!