How do I check collimation and if needed collimate my C9.25?

[KE400]

Hi

I'm just trying to image Jupiter again at the moment and questioning the collimation of my scope. Can someone please explain to me in simple terms how I actually check it and if needed, how do I actually collimate it?

Help & advice much appreciated

Thanks for taking a look

[The Bat]

You may have trouble focusing on Jupiter if your collimation is out. You may notice as you try to bring it to focus that it always appears to be fuzzy, and always on one side, whichever way you turn the focus knob. I noticed that when I bought my C8 that I could never quite get Saturn in focus and it was always one side that was fuzzy.

Alternatively, point the scope at a brightish star (near the zenith ideally) and de-focus it. If the scope is collimated you should see a doughnut shape which should be pretty much round. If it is squashed or the hole is off centre, then your collimation is out. A perfectly collimated scope should show concentric rings on an out of focus star.

There will be 3 screws holding the secondary mirror which are located on the central obstruction in the middle of the corrector plate. These may be covered by a cap that you need to flip off (I have to use a small screwdriver to do this). You will need to work out which screw has to be adjusted (if you have the instruction manual, there should be a guide to collimation in there). While centred on an out of focus star at high power you need to tweak the screw very slightly (often 1/8 of a turn or less at a time), re-centring the star after each adjustment. Continue making adjustments until you get the concentric rings. You may have to adjust the other screws in the opposite direction too. It should only require fractions of a turn. My description is not great and I would recommend reading a collimation guide with diagrams which should make it clearer. There are plenty floating around on the internet.

Hope that helps a bit.

Rachel

[KE400]

Thanks Rachel

Having read your reply it looks as though out of collimation is my problem. I'll take a look around on the net too before attempting anything.

Thanks again

[r3i]

Hi Kevin,

One of the tricky things when collimating an SCT is working out which of the knobs on the secondary you need to tweak to make the right adjustment.

I came across an article which describes a simple yet cunning device which helps: The Sheer Genius Collimation Device: Astromart Reviews - SCT Collimation under Adverse Circumstances

[cgarry]

This is the best link that I have found about SCT collimation:

Thierry Legault - The collimation

Cheers,

Chris

[KE400]

Thanks guys, will take a look