Obsession UC 18''

I wouldn't worry about the secondary mirror, that case looks like it will be taken as cargo hold luggage and so what if it cost a few euro more.
if I didn't have the 20" already, I would very seriously go for this scope, definitely worth the effort in transporting it.

...enter the Argo Navis and Servo Cat system!


I guess I may as well get my new avitar sorted too...

Lovin' it Frank!

Lads,
Just saw a review of the 18" UC on the obsession yahoo group, looks like a very honest review with good and bad points. Worth a a read (I got Toms permission before posing).


18” Ultra-Compact Obsession Telescope Review
by Tom Polakis and Gordon Pegue

I have had my 18” Ultra-Compact Obsession (S/N #38) for nearly a month now. It was delivered more than 6 weeks ahead of the promised date, which has enabled me to assess it before the monsoon rolls into Arizona. After several sessions from my driveway, I was able to put it through its paces at a star party at a very dark, high-elevation Arizona site 40 miles south of Flagstaff this past weekend. Off the obsessionusers list, Gordon Pegue (S/N #4) and I have been discussing this telescopes good and not-so-good points. We have also communicated most of them directly to Dave Kriege, so little of this informal review should be news to him.

Both Gordon and I agree that the telescope succeeds spectacularly at doing what it is advertised to do. The telescope provides exceptionally sharp and contrasty images in a package that requires only the smallest of ladders for viewing at the zenith. It folds up into a remarkably small volume in a very short time. These features overcome any of the design deficiencies that Gordon and I have been discussing. After reading the following paragraphs, come back to this one for our final impression, which is one of a great star party travel telescope that packs a lot of aperture into a small package. And the figure and smoothness of the OMI mirror is almost beyond belief, particularly at f/4.2.

On to the inevitable complaints. Like many on this list, both Gordon and I have been in the hobby for many decades, and have used a lot of telescopes. While we know how to modify telescopes to make them usable, we would rather have a complete telescope after an outlay that exceeds $7000. The Obsession U-C’s that we received are not complete telescopes. And the irony is that making them so would not require much in the way of design and construction effort or expenditure.

A cooling fan is mounted behind the primary mirror. Before reading the manual, I looked in vain on the scope for an on-off switch and through the four boxes for the power supply. Neither is provided, and recommendations are made in the manual for suitable power supply options. Folks at the star party invariably thought that a complete, mounted fan system should be provided, and were put off by the two dangling wires.

There is a maddening starting friction in the altitude bearing. Since the Ebony star moving altitude bearing surface has to be split in Kriege’s ingenious folding design, he uses a continuous strip of Teflon rather that discrete pads for the stationary bearing surface. Gordon found it next to impossible to make small corrections in altitude, and suspects that the stiction is due to binding along this surface. I concur, and by “small corrections” we mean on the order of a half a degree. Everybody who tried to move the telescope to center an object found themselves overshooting grossly in altitude. Fortunately, my scope was riding on a tracking platform, so corrections were not needed often. The use of subsidiary products like wax and Armour-All should not be a requirement to achieve smooth altitude motions!

The upper Kydex light baffle that extends away from the scope opposite of the focuser is at least 4 inches too short. It would be a perfectly adequate design if the focuser were “submerged” into a true upper cage assembly, but the focuser hangs a few inches beyond the upper “cage” on the U-C. The baffle is ineffective at blocking stray light that enters the focuser. And this problem does not only manifest itself when streetlights are present. At my dark site (SQM 21.7), the gray of the night sky entered part of the field of view, contaminating the view to the point of making certain eyepieces unusable. The Naglers that focused inward in the focuser’s travel were affected the most. Gordon reports that using his 31mm Nagler (requiring the most in-travel) results in very poor views due to the extraneous light incursion. My wife Jennifer was able to remedy the problem at 10 p.m. using only duct tape and a cannibalized box of Fruity O’s, as shown here: members.cox.net/tpolakis/astro/baffle.jpg

In the incomplete telescope department, neither Gordon or I were happy about having to buy our own lead shot for the counterweight. I understand that this would add weight and shipping expense, but again, I don’t wish to become an ATM when I receive my new telescope, even if it’s a Dobsonian.

This was my first experience with a sling-supported primary mirror, and Dave did a nice job of documenting the method of adjustment. I was a bit put off, however, when the mirror moved laterally by at least a quarter of an inch between the two stand-off posts. It would certainly move like that when mounted on an equatorial platform. Dave’s reply to this complaint of mine was that the idea of inserting foam pads between the primary’s edge and the posts has been on obsessionusers for a while. A better approach would be to provide the telescope with two custom fitted, cylindrical foam pieces that can be added after the mirror is correctly positioned in the sling.

Gordon was not ready for the weight of the loaded travel case, which is certainly not something that anybody weaker than Hossein Rezazadeh ( members.cox.net/tpolakis/astro/Rezazadeh.jpg ) can actually lift. Gordon does a lot of solo observing, and cannot use the travel case. The Virtual Mirror Box with the primary is manageable to lift into a vehicle, but the loaded case is not. Since I am prone to damaging things in the bed of my little pickup truck, I greatly appreciate a complete, protected telescope in such a small volume, and Jennifer and I are able to lift and slide it with some difficulty. I understand that this adds volume, but some way of attaching the wheelbarrow handles to the case might be a great improvement.

Slightly more nit-picky is the complaint that the ground board feet are too low. Care must be taken to insure that the ground board assembly is properly positioned with no interference from objects on the ground before placing the VMB assembly.

The azimuth encoder has pretty delicate protection. It would not be too difficult to fabricate a small metal encoder cover for those scopes that are ordered with
encoders pre-installed.

Finally, the manual is in need of copyediting. The manual refers to non-existent figures in several places, and suffers from poor organization. Since this is a new telescope design with new design innovations, the associated terminology really needs to be described with a labeled layout drawing.

Now I must direct you back to the second paragraph, where I wrote all those good things about the telescope. None of my complaints prevented us from thoroughly enjoying the views at the dark site, although the upper baffle deficiency almost did. The scope is light enough to track on a Tom O. platform that was designed for my 10” Dob. Dave did a lot right with this telescope, and I’d give it 4 out of 5 stars. With a price increase of less than 5% completely transferred to the customer, the 18” Ultra-Compact Obsession would be a 5-star telescope.

Hmm. Interesting review.
So, mabey if you hang on for a year or so, they might have ironed out those little issues mabey?

That's my plan exactly!
Thanks for posting the review Dave.

Yes thanks, Dave.
Again, it seems that the weight might be a bit too much to make it that portable, despite the interesting design.
I've back problems, and after initially lifting the constituent parts of my 16" Lightbridge by myself, I would never do it now....the 12" was about my limit, so it's a pity that it's still not really an option with this model.
The mention of that movement in the slinged primary mirror sounds worrying too.