Keeping Collimation with my Celestron C11 (not the Edge HD)

[Jane C]

Hi: 

I'm able to collimate my C11 just fine.  I use the GoldFocus system with the supplied Tri-Bahtinov mask.

The frustration is that it doesn't stay collimated.  I'm wondering why this is.   I have various thoughts.

I should perhaps  mention that the telescope is fixed in an observatory building.

1. It's a differential cooling issue.  We have had some hot weather lately in Wales. (Cooling is well known to affect focus, so why not collimation?)

2.  Something is loose somewhere.  I don't think it is the secondary mirror: I make sure all three Bob's knobs feel a bit tight.  What else could be loose?  If the primary is loose, how do I fix it?

3. Something totally else.  Any suggestions welcome.

Thanks in advance,

Jane.

Edited August 28, 2022 by Jane C
Omitted sentence

[dan_adi]

SCTs are not known as high quality products. Maybe you were just unlucky and got a bad one.

[dweller25]

I never had a C11 but does the primary have a locking nut around the primary baffle ?
If so it may need snugging up ?

This may help…..

https://astroshed.com/observatory/c11saga/c11saga.htm

Edited August 29, 2022 by dweller25

[CraigT82]

Is this something that has just started happening or has been happening the whole time? 
 

It’s a fairly simple test to check if it is differential cooling. Collimate the scope and then leave where it is without moving it and come back to check later. If it is cooling the collimation might shift without having moved the scope. 

More likely to be the primary mirror shifting. Any moving mirror scope is going to have issues with mirror flop to a certain extent. Not sure how you can remedy that though, sorry. 

 

[newbie alert]

Bobs knobs..

[Jane C]

I already have Bob's Knobs, but thanks for the thought.  🙂

[newbie alert]

1 hour ago, Jane C said:

I already have Bob's Knobs, but thanks for the thought.  🙂

No it's the bobs knobs is the reason... They're easier to collimate but you will have to collimate more often.. don't think they hold the secondary tight enough