Obsession 18" f/4.2 UC Question

Greetings,

I am wondering if an owner of the Obsession 18" f/4.2 Dob can comment on its stability and ability to hold collimation trough a night of observing?
Thanks,
Greg W

Greg Wing said:

Greetings,

I am wondering if an owner of the Obsession 18" f/4.2 Dob can comment on its stability and ability to hold collimation trough a night of observing?
Thanks,
Greg W

No one has any input to my question? Thanks-Greg W

I once owned one. Collimation was pretty stable through the night. There was one collimation issue I noticed. The focuser was mounted on the upper ring between two of the support trusses. The ring flexed a little bit between viewing at low and high elevations, so the focuser and hence collimation would shift a tiny bit. But if you collimated at say 20 degrees from the zenith, and observed within say 40 degrees of the zenith, it wasn't too bad. I think a stiffer upper ring would help -- a carbon fiber upper ring would be nice but also very expensive. One could also add some thin extra trusses at the focuser to give the upper ring more support there -- maybe run the thin trusses to the normal truss poles.

I had an Obsession 18" UC. The only good thing about it was the mirror, and that was from OMI

The truss poles were the wrong length and the mirror sling was too short, so the sling kept falling off. Has some other issues too, for $7000 new scope. I didn't know any better at the time.

If I had bought a classic I might feel differently..

My criteria for a new dob is the vendor tests the complete functions of the scope at night under the stars before delivery. Also the eyepiece height must allow seated observing at zenith, unless it's 27" mirror or larger.
John