how do you collimate a Celestron SCT?

[dc509]

Hi

Noticed the other night that the out-of-focus donuts were slightly off-centre in the middle, which I assume means that I should collimate the scope. I've heard that replacing the secondary's screws with Bob's Knobs will help, but what else will I need? Is there a tutorial anywhere? Have had a search but most content is aimed at Newts.

Many thanks

d

[John]

This might help:

Schmidt Cassegrain telescope advice - maintenance - SCT collimation

Try and get it as accurate as possible. SCT's are very sensitive to mis-collimation, contrast and resolution suffer quite a lot. Once collimated they tend to hold it longer than newts.

[riklaunim]

You can collimate with normal screws as well. I check collimation from time to time before imaging using the planetary camera:

So I can look at the image when colimating And it's higher resolution than visual. It just needs to be nice and round and centered.

[cgarry]

This might help:

Schmidt Cassegrain telescope advice - maintenance - SCT collimation

Try and get it as accurate as possible. SCT's are very sensitive to mis-collimation, contrast and resolution suffer quite a lot. Once collimated they tend to hold it longer than newts.

Yes, an SCT can feel like a whole new instrument after if has been well collimated. It is well worth checking collimation, especially since it only takes a few seconds.

Chris

[red dwalf]

buying a set of bob`s knobs does make the whole process alot easier as holding and adjusting a screw driver round the front while looking round the back is very difficult,

one tip i found was when adjusting the collmination, point your finger over the front of the collecter plate while looking through the eyepiece and move finger around the rim until you come to the side that needs adjusting (circles through eyepiece look set to one side) then it`s easy to see which screw needs adjusting.

hope that helps alittle

[cgarry]

You can collimate with normal screws as well. I check collimation from time to time before imaging using the planetary camera:

So I can look at the image when colimating And it's higher resolution than visual. It just needs to be nice and round and centered.

I find that I have to use a camera as my arms are not long enough to reach the front of 9.25" SCT whilst looking through the EP! Plus I would really not want to try and use a screwdriver at the front of an SCT while looking through the EP, Bob's Knobs rule!

[Trevor-Austin]

I've got the equivalent Meade (2nd one I've owned) and bobs knobs was my first add-on, followed by the peterson mods.

Makes collimation a literal 1-3 minutes and I do it every time I view now it's that easy.

[dc509]

Hugely helpful as ever - thanks very much for the advice. Like the idea of using a planetary cam to get round the "long arms" problem!

Many thanks again...

d

[Mike_F]

You can collimate with normal screws as well. I check collimation from time to time before imaging using the planetary camera:

So I can look at the image when colimating And it's higher resolution than visual. It just needs to be nice and round and centered.

Just out of interest..

Is it the effect of seeing / heat currents, or is that central dark region slightly off centered to the top and right in that shot?

In addition - posting that has been helpful for me, because I can't see the central bright spot in the defocused image (as shown in all the lovely online collimation imagery) through my C11 - and have been worried that it itself was some kind of collimation problem.

Your image represents exactly what it looks like through my scope.

[riklaunim]

It's a single frame from DSI III Pro, and it's slightly miscollimated. With 2x Barlow it looked like so:

Air currents from primary look like this:

So I've made a cat blow-through cooler: http://oi55.tinypic.com/aw6kqw.jpg

[Psychobilly]

FOr me its...

Bobs Knobs, A webcam with Metaguide and a LED artificial star... (even better with a DMK @ 60 FPS ...)

Billy...