Prospective Obsession (or other large Dob owner) w

Hello:

I posted the post below in the Obsession group on Yahoo, but it might be more appropriate in a general discussion group. I received some very helpful responses and would appreciate any further assistance. Thank you in advance.


I am soon approaching the "purchase point" for a scope in the
20" to 25" range. I have narrowed my choices to Obsession, NighSky,
and Teeter. I have done so much research that I am coming to a point
of diminishing returns. I also have reviewed the Obsession video.
I did have a few final questions that I was hoping Obsession owners
could address. I would be greatly appreciateive of any help. I also
will be visiting an Obsession 20" owner in a few weeks who was kind
enough to invite me to take a look through his scope.

Just for background, I am a serious observer, though, virtually
all of my experience has been with large scts (12, 14, and 16). I am
not particularly mechanically inclined, not a dummy, but not very
good at it and I do not have time to learn. My knowledge of optical
theory is minimal. I just really enjoy observing. Visual only.

My concerns and questions regarding Obsession are:

1. Sling v. removable cell: can the mirror really be left in
the scope for transport by van over bumpy, though not too bad,
roads? Is the mirror held securely especially when viewing low in
the sky? Is the mirror held correctly to avoid or minimize
astigmatism? Does collimation hold throughout the night?

2. F/5 v. F/4.5 and use of a paracorr. Here is where my
inexperience really comes in--lack of observing time through large
dobs. I know comfort and preference varies among individuals, but is
a paracorr necessary at F/4.5? Does a paracorr significantly dim the
image, i.e., more glass in the way? Or is this just minimal for
objects just on the edge of visibility? Once on a ladder, does it
matter if you are on the 3rd or 5th step, comfort wise ("heights" is
not an issue). Is the smaller central obstruction really an issue
given the relatively small size of it at either focal ratio?

3. Enhanced coatings. Are scatter or roughening of the
mirror's figure really an issue? If these do occur, is the extra
half dozen percent in brightness worth it?

4. I like how NightSky and Teeter have "electronics packages"
where the jacks, power supply, extra fans, dew control, etc., are all
installed. This "complete package" does not seem to be an option for
Obsession and I will not be drilling into the scope myself. Nor do I
feel like shipping it to a third party vendor. How do I get around
this?

5. Is it significant that the Obsession structure and mirror
come seperately and are not tested as a unit before going to the
customer?

6. Has what appears to be an increased production run by
Obsession lessened quality or introduced mass production
disadvantages?

7. How do Obsessions hold up over the years? I rememebr seeing
a couple of them at the NEAF show two years ago and was a bit
dissapointed by what looked like very visible wear and tear (i.e.,
flocking of the uta peeling off)?

8. Can the mirror be cleaned whiile staying in the scope if the
scope has the ServoCat and ArgoNavis installed?

I think that is it. Any assistance is very much appreciated.
Thank you in advance.

Gregg D. Bernstein
Augusta, Maine

Gregg, rather than getting into a long diatribe, I'll just suggest that you take a hard look at the Starmaster 20" and 24" scopes before you make your decision.

(For anyone else, this isn't an invitation for a debate - it's just my opinion on an important option.)

Doug

A couple weeks ago I picked up an 18" Obsession from Dave Kriege at Astrofest. Last weekend I delivered it to my friend in Michigan (I'm in Wisconsin). This was all OKed by Dave, we're old dob building buddies from the late 80's. I had a chance to use the 18" at Astrofest through some sucker holes and it performed beautifully. I was very impressed by it since it was an f/4.5 mirror (Torus). The views were wonderful. Had a hard time giving it up to the new owner. As an aside here, I was buying the new Obsession owner's used Starsplitter 15" f/5 dob. I've had it in the back yard a couple of times and it handles very nicely too. The Swayze mirror is excellent.

I would not hesitate to buy a new dob from either company or the others you have mentioned. And to echo another's advice, put Starmaster on your list too.

I will say this about Obsessions. Dave tries to keep mirrors in stock so his turn around time is very fast. My friend ordered his 18" about two weeks before Astrofest. Another person at Astrofest ordered a new 18" and Dave told him he could pick it up the following week.

Don Wyman

Thank you all for your helpful information. I am off to Mass. in a week or so to look through a 20" Obsession!

Gregg