Collimation issue

[Darien]

Good Evening Everyone,

I have bob's Knobs on my 8" SCT... Was wondering if there's a way to tighten the knobs but also keep it collimated. Its stressful having to collimate my SCT everynight. Any suggestions?

Best regards,

Darien

[Akiainavas]

Are you sure that knobs are the issue ? SCT telescopes rarely need collimating - frankly speaking, once collimated, many of them don't have to be collimated for years unless you remove secondary on a regular basis or bump it very badly.

My EdgeHD was only collimated once, and after over 9 months of regular use and transporting it to a dark side - it still produces perfectly sharp image and passes star-test each time.

Do you use Fastar/Hyperstar ?

[Davey-T]

I've had my SCT since God was a boy and it's never needed collimating.

Dave

[Akiainavas]

Darien, let us know what exactly is happening. Is your scope failing star-test ? It might be that those knobs are not suitable, viewing conditions are not good or perhaps ( hope not ) the optics are defect ?

[PeterCPC]

As above, my C9.25 was collimated using Bob's Knobs over a year ago and is still ok. You only tighten the knobs as far as you need to achieve collimation.

Peter

[faulksy]

are the bolts loose, was you scared to tighten them after colimation incase it moved again. this is probably the reason

[Darien]

Hello everyone sorry for the slow replies... When I first bought this my Junior of high school and well into deep space imaging my star threshold in DSS only picked up so many stars. The following night I put Deneb on high power and noticed it was out of collimation (donut) now I was able to do adjustments to get the perfect donut but I didn't know how to tighten it to keep it that and every since I've doing the same routine:/ I appreciate your help guys

 

Darien 

[Ceramus]

I've had an 200mm SCT for 15 years and hardly ever needed to collimate it. Good to make sure the scope has cooled down and the seeing is good before a star test.

here's an usefull site:

Skywatch.braniac.com/collimation.pdf

[Darien]

And yes the Bob's Knobs are the correct threads for the the C8. Would like to get this fixed before going to Texas Tech and also because I'm currently on standby because of the moon in finishing the remaining 6hrs on the fireworks Galaxy.

Darien

[Akiainavas]

On 17/07/2016 at 06:27, Darien said:

 but I didn't know how to tighten it to keep it that and every since I've doing the same routine:/ I appreciate your help guys

Darien 

I'm afraid there is no way to 'tighten' or lock them. You loosen or tighten them to collimate/move the mirror around, but once you're done, you should just leave them be and they should not move.

You should not have to repeat the procedure, or at least not very often. If that's the case then either the secondary mounting is poor or perhaps the threading on your Bob's Knobs or the secondary holder are at fault. Have you tried reverting to original setup and checking whether the issue persists ?

[Darien]

The bobs knobs are the correct threads for the secondary mirror.. Now I do believe I have the factory set screws because I ordered some before getting the bobs knobs

 

[Darien]

Should I try those?

 

[Akiainavas]

13 hours ago, Darien said:

Should I try those?

 

Yes, I would suggest that. This might help you identify the problem - it it'll hold, it means there might be something wrong with Bob's Knobs. If it won't hold, then it might be the secondary holder.

By suggesting that maybe threading is not good on your knobs I meant that perhaps it's worn or damaged, not that it's incorrect. Unfortunately, sometimes it does happen.

[Dave In Vermont]

One trick everyone who is planning to install 'Bob's Knobs' should know is to be sure to install them one-at-a-time. Do NOT take all of the old one's out - and then install the new one's. Doing so will toss your current collimation-settings out-the-window. This will make your collimation be really messed-up and all the more difficult than it need be.

Have fun,

Dave

[Darien]

9 hours ago, Dave In Vermont said:

One trick everyone who is planning to install 'Bob's Knobs' should know is to be sure to install them one-at-a-time. Do NOT take all of the old one's out - and then install the new one's. Doing so will toss your current collimation-settings out-the-window. This will make your collimation be really messed-up and all the more difficult than it need be.

Have fun,

Dave

Unfortunately that's what I did.Gross