Obsession Telescopes are the de facto standard in non-mass market quality dobsonians with premium optics.
(A dobsonian is generic term for a telescope resting within an inexpensive base wtih sliding azimuth and altitude bearings - rather than mated to a precision-geared mount head supported by a tripod).
Dave Kriege's The Dobsonian Telescope is the Bible for building your own dobsonian scope. "Obsession-clone" is the designation for the majority of dobsonians, either boutique-built or DIYer-built. Obsession-closes are the Jello and the Cokes of dobsonians. They're excellent.
They're excellent, but they're not small and they're not light. You generally roll them up a ramp into your truck or van to take them to your dark sky observing site.
Dave renamed these traditional "big box" dobsonians "Obsession Classics" when he introduced a second style of scopes: the Ultra-Compact series. The Ultra-Compacts are designed to be lighter and more portable.
I bought an Ultra-Compact 18" (UC18). At the time, it was the biggest scope I could use both at home and at a dark site. My home observing area was upstairs. I could carry the entire scope from upstairs to the car in two trips. I would not be able to do that with any 15" or larger Obsession-Classic or clone (removing the mirror and carrying separately would be required to keep the weight down. The third trip is less of an issue than removing and re-installing the mirror.).
Now that I don't observe from ground level at home, I can roll the scope intact to the car or to my observing area, the ability to carry the scope is far less important, though the transportability in a compact SUV or a sedan is still important.
The Ultra-Compact series is designed to fit in its ATA Travel Case, so that you can fly all over the world with it (checked-in, of course). That's the overriding engineering constraint. All designs are a compromise, and the major donor from the UCs' design is its ultra-compact lower hardware - broken into a very low-profile groundboard and a very complicated Virtual Mirror Box.
Where this immediately becomes an issue is the requirement for a custom dolly if you want to be able to quickly pop outside to observe.
Below our some videos about this very portable and capable (but potentially finicky) telescope:
- Here''s an Introduction to the UC18 and a custom dolly to make it fast to Grab-and-Go start observing.
- Here's why an Obsession Ultra Compact Needs a dolly
- Here's the most annoying challenge in using the UC18 with GoTo
- Details of the groundboard and Virtual Mirror Box.
The following are some customizations I made: