Serious aperture

The observant reader might have guessed that it would be only a matter of time before I had to get a bigger telescope. I even admitted that I was still obsessed last October. I ended up with an Obsession 18" Ultra Compact, which is at the very limit of what I can manage by myself. As advertised, it easily fits into the back of my car.

It is wonderful, but in spite of the price, it doesn't really arrive complete: there is lots of customization to be done. The rear mirror fan simply has two wired dangling: it is up to you to figure out how to connect them to the power supply. I connected it to an N-size coaxial connector, the same that is used on the Argo Navis for external power. Then, there is the issue of power; I discovered that the 1.2 Ah gel cells fit conveniently in the base, under the mirror, so it was just a matter of making an appropriate cable.

First light was almost a disaster. I had failed to fully assimilate the instructions for the Argo Navis digital setting circles, so it wasn't until second viewing before I figured out how to align that correctly. Perhaps most serious was that the spider on the upper tube assembly was not centered, so I had poorly collimated images; fortunately, I was able to correct that before the second viewing.

The mirror – the heaviest and most expensive piece of the entire scope – is now suspended with a cable, rather than a strap. Obsession's approach to this is ingenious and inexpensive, but requires occasional manual intervention. I discovered that Howie Glatter has an elegant custom machined replacement that is a huge improvement; I was able to get that before the mirror arrived.

The Ultra Compact leaves the mirror very exposed. There is a Kydex light baffle that attaches via velcro to two points; a rather flimsy approach, so I added two more attachment points to improve that. Finally, the upper light baffle supplied is too small, so that ambient light "leaks" in; I'm not sure why Obsession designed it that way, because it is a well known issue; perhaps because it made the scope look smaller and sleeker. Fortunately, I was able to obtain a sheet of Kydex and make one that will block a lot more of the light.

It was worth it to do the final touches myself. Obsession really grew out of a do-it-yourself world, anyway. Now I have it the way I want it.

So, I have an 18" scope again. I fooled myself into thinking that I had seen everything worth seeing with an 18". In fact, that was an expression of frustration over aging eyesight. My premium 4" refractor has pretty views, but there is nothing like serious aperture! My second "first light" was supremely satisfying, filled with views of galaxy clusters in Virgo. I'm just itching to get again.