Used 18" Obsession, what to look for?
Posted 08 July 2013 - 02:17 AM
Since I've mostly been an sct guy, what should look for?
I've read lots and lots but it's always good to check for tips.
Posted 08 July 2013 - 07:01 AM
--Look to see that the scope is at least roughly collimated, i.e., viewing through the focuser shows proper alignment of the reflections. This will tell you that everything fits together properly. If a laser is available you can check for movement of the spot as the scope is raised and lowered in altitude. Spot movement will indicate that there is a source of flexure, such as wear on the truss connectors.
--How are the motions in azimuth and altitude? They should be smooth but not loose.
--Make sure the mirror surface has no clamshells or other defects. Small issues can be tolerated at an appropriate price.
--How is the finish of the scope? Maybe you can renew the finish if necessary; what you don't want is a lot of parts that have become warped or severely corroded by exposure to the elements.
Posted 08 July 2013 - 08:10 AM
Posted 08 July 2013 - 02:48 PM
Posted 08 July 2013 - 09:35 PM
Will definitely check Collimation and check the movement too.
Posted 10 July 2013 - 12:18 AM
Posted 10 July 2013 - 10:41 AM
I'll probably keep my C11 for taking along when we are camping as I don't think I can load the Obsession into the camper and keep it safe in there when not using it. I live in a yellow zone so it's not too bad at home.
Posted 10 July 2013 - 01:26 PM
I have a "exhausting" fan set in a sealed rear baffle coupled with the Teeter-style boundary layer fans. Had a similar set-up on the Ob. The boundary layer fans improve the view for well over 2 hours, so I'd say it takes 2 hours in general for things to settle down to a reasonable degree. Truly, it never reaches ambient. But first hour I would typically use binocs or do something else while the scope cooled.
Endorse the advice to check all bolts and tighten as necessary. Both my dobs would/do loosen over time....but I trailer the scope and things vibrate more. That's the number one reason for collimation drift for these scopes in my experience: loose bolt somewhere. Split block (which holds the truss tube) loose on an Ob. Teeter alt bearing bolts loosen also. Spider vane bolts.
Use blue loctite judiciously to reduce this tendency on the split block screws, but it'll happen either way...
Also carefully check the tailgate, mirror cell and collimation bolts. Make sure the mirror is resting on the pads, and check the back of the mirror for evidence of trauma. More than a few times I've seen damage from mis-handling in older mirrors that have been around the block...If there is a crack or splintering anywhere on the mirror, walk away.....
Posted 24 July 2013 - 10:10 AM
Posted 24 July 2013 - 08:50 PM
An 18" Obsession is a great sized scope.
Posted 27 July 2013 - 11:15 AM
The man was very very helpful and showed me everything, so much so that he answered most of the questions you guys gave me. I also had the collimation laser on and when from zenith to about 20deg and no movement of the laser!
Will give a first light report when I get a chance.
Posted 27 July 2013 - 01:29 PM
Congrats on your new super scope. You will likely enter a new era of happiness under the stars