Want to sell: My 18-inch Obsession Classic

[Akarsh Simha]

I think I've come to terms with the idea of selling my 18" telescope. The last I used it was in December 2024 when I still hadn't figured out how to set up and tear down the 28-inch on my own. The 18" is a lot easier to set up and move than my 28-inch, but I have learned that I probably won't use it. For portability, I have a 12" now.

The mirror is an OMI-made 18" f/4.5 that I got second hand. The mirror was last recoated by OMI in August 2017 or so just before they went out of business. The secondary mirror is a dielectric secondary as was typical of Obsession and does not need recoating. The previous owner, John Tatarchuk, was apparently displeased with the mirror at first and sent it back to OMI for re-figuring, so allegedly it is a re-figured mirror. Alan Agrawal star-tested the mirror and you can ask him for his honest opinion if he remembers :-), he said there was a tiny bit of spherical aberration. But you don't need to rely on the star test (in fact it doesn't give the full picture for deep-sky observers), I have a huge list of observation reports with that mirror including the 10 galaxies in the Corona Borealis cluster which to my knowledge is a record with an 18-inch. Of course, that had more to do with sky conditions than the mirror -- I typically see six galaxies which is the norm for an 18", but my 18" has been able to fairly consistently reproduce many of Steve Gottlieb's observations with his 17.5" and Zambuto-figured 18" telescopes.

The structure is fully functional, but devoid of any aesthetic appeal. If you care about how your telescope looks, not what it shows you, this is not the telescope for you; unless you're willing to varnish it and clean it up. There are lots of hacky fixes on the structure; a buyer with resources (money or time) would ideally rebuild the structure, even though there is nothing impeding usage as of today. Most recent hack was that I messed up the locking nut for the JMI crayford focuser on it, and had to drill it out and put a different screw. It works, but as I said, you won't get anything but a "wow, that's a beat up telescope" at a star party. You would also probably want to do something about the truss clamping system. It works, but it is far from ideal. Obsession's clamping system is superseded by much more convenient systems today, and the old wooden clamps on it are getting rickety. Here's the deal though: I have access to a bunch of woodworking and metalworking tools, and if you're willing to invest the money in a new clamping system of your choice (probably Aurora precision, which is expensive but the best; ), I could spend a weekend helping you re-do the clamps or such.

I made a few upgrades from the standard Obsession over the years, and the most notable one is a Glatter sling. The old "seat belt" sling from Obsession has the propensity to produce astigmatism from time-to-time which the Glatter sling does not. Except, a Glatter sling cannot be used with an equatorial platform, so even though I have a Gregg Blandin equatorial platform that I want to sell as well, I would probably sell that separately. The other upgrade is an adjustable counterweight system from Markless Astronomics. A light shroud from Astrosystems (with a small hole), a dust cover from Astrosystems (no issues) that I got from the original owner will be included.

Now comes the price. If you offered me $3600, I would give it to you today. The telescope has more meaning and sentimental value to me than any money I would get for it, so I think the bigger compensation I could get for it is the joy of reading someone else's ORs with it. Which means that I would settle for quite a chunk less, first if it were a TACo, and second if it were someone who would post ORs with it when they take it out. The main motivation for me to sell it is the space it is occupying in my apartment now that I've upgraded.

Clear Skies

Akarsh

[Akarsh Simha]

Forgot to mention there's also Obsession's original wheelbarrow handles. The tyres are pneumatic, you may wanna replace them with non-pneumatic tires if you please.

[Ted Hauter]

Deal of the year!

On Sat, Sep 27, 2025, 4:25 PM Akarsh Simha <akars...@gmail.com> wrote:

Forgot to mention there's also Obsession's original wheelbarrow handles. The tyres are pneumatic, you may wanna replace them with non-pneumatic tires if you please.

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[Stacy Jo McDermott]

It's a beautiful telescope. 

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