Collimating an SCT

[Ags]

I have now attached Bob's Knobs to my C6 and seem to get reasonable results with collimation. But I find the collimation screws turn with no resistance at all? Is that normal? It doesn't give me confidence that the scope will hold collimation in the long run.

When collimating, I favor tightening over loosening, but sometimes a bit of loosening is unavoidable.

Am I doing anything wrong?

[noah4x4]

Yes, I found the problem with Bob's Knobs is that they don't hold collimation as well as original Phillips screws. You can never apply enough torque with them.  I was forever having to adjust them and  regretted adopting them. After a month of frustration I restored the Phillips screws where 1/8th turn (with enough torque) is desirable. I would only recommend Bob's Knobs if you are prepared to collimate every other session, and definitely not recommended for Hyperstar users that regularly handle their secondary mirror. Phillips screws are far more snug.

 

Edited July 19, 2020 by noah4x4

[Ags]

I got the collimation just right last night, but it was half an hour of wasted time. Hopefully it will hold for a few sessions.

[Mr Spock]

I use Bob's Knobs on my C9.25 and they are just fine. I don't know why yours would be loose. 

I don't think I've touched my collimation in at least a year. Every time I do a star test it looks spot on.

[Ken82]

🤔 ive also found bobs knobs to hold collimation. 
 

maybe tighten them slightly before starting collimation. Sounds odd 

[billhinge]

My Bob's knobs seem quite stiff to me. I bought one of the Hotech laser devices many years back https://www.firstlightoptics.com/hotech-collimation-tools/hotech-advanced-ct-laser-collimator.html unfortunately I was using a CG5 to hold the 11" SCT and it wasn't stable enough so I stopped using it and moved to a more manageable 80mm APO.

I've now bought an EQ6-r so will try the SCT again, I uncovered it the other day and it looks fine, mirror still seems clean and bright

My gripe with Bobs knobs is I didn't like the thread on the outside, could be a bit painful on the fingers!