culminate a cpc 1100

[dutch queen (Franciscus)]

does anyone know how to do this, is it possable at all, i am a little underwelmed with the viewing out of my newish cpc 1100
tnx

[Allan_L (Allan)]

I had a CPC1100 for three years and neither I nor the previous owner ever needed to collimate it.
Several experts checked it and all agreed it was perfect.
However, not all scopes are this lucky.

The first thing is make sure you really need to before adjusting anything.
The defocus star test should confirm your diagnosis.

From memory, collimation is described in the manual.

Or try this link to the Celestron site:
http://www.celestron.com/c3/support3...articleid=1974

Hope this helps.
Al

[The_bluester (Paul)]

My CPC925 was a little off the mark out of the box. I had a couple of goes at it and thought I had it pretty right. But a recent star party left me realising it compared poorly to other scopes on the field. A nearby 18" dob produced star images that were much crisper and tighter.

I invested in some Bob's Knobs as I think the collimation screws on the CPC925 were just silly (Imagine making you wave a small, pointy screwdiver around the corrector plate in the dark!) I actually bought a set off here cheap (They were for a C11 and I bought them on the off chance they would fit, From Allan_L as it happens, unfortunatly they did not so I bought a set of the right ones direct from Bob's Knobs, the C925 secondary sits slightly further out from the housing so the C11 ones are not quite long enough)

After fitting the new ones up and guessing the mirror alignment on the bench (Long story! The install instructions suggest that you remove one screw at a time and count the turns so your collimation should be close enough to begin with when you put them all in, but as soon as I removed one the mirror moved away a little on that side and the screws would not reach to pull it back in, so I had to remove the secondary to fit them, thankfully that is easy to do with the triffid "Fastar" secondary)

After guessing the collimation on the bench I tried it out and it was nearly spot on, actually much better than I had done it before, a small tweak and it is about as good as I reckon I am going to manage and the scope now produces much tighter, cleaner star images, but I have not had a chance to really try it out due to that muddy thing we are calling a sky and work never coinciding with a clear day on both counts!

Basically, I second what Allan said, check the collimation before you get too unhappy. The SCT scopes seem to hold it pretty well (Mine did not appear to change in a year and a bit with the scope carted about in my car a number of times) but if it is not right to begin with then it will nicely hold the poor collimation for you as well.

[Shiraz (Ray)]

hi Franciscus. maybe you could give the forum an idea of what is wrong with your views through the scope. Seeing can be pretty ordinary this time of year - could be just that. If there are identifiable distortions, someone here will know what needs adjusting. regards Ray

[g__day (Matthew)]

Can you attach a DSLR to your OTA and take a shot?

My prefered method to check optics for collimation is select a single bright star, centre it and defocus it until it takes up about half the DSLR photo size (so the stars defocused size is about the size of the full moon) and take a 3 to 10 second image and post it here. Such a shot will create a doughnut effect. Then you simply check to see is the dark hole of the doughnut in the precise centre. If not - you need to collimate! Always try and recentre the star before you adjust collimation (so focus star, centre, defocus, adjust collimation, then refocus, re centre, defocus - image check collimation etc over and over).

Once collimated optimally at the centre of your viewing - refocus the star (any Bhatinov mask really helps with this), then move to a object with alot of stars across the whole image. Eta Carina or LMC suit this well enough. Take a 30 second to 2 minute shot and see how curved or flat your field of view is - namely is the centre of your shot nice and tight but the corners streaked or stars strecthed away from the centre. If so you have coma and may need a coma corrector.