8" cat problems

[Gazabone]

Hi,

Hoping someone can offer some advice here please. I have a 2nd hand Celestron C8 with motofocus. The collomination is badly out and I can't seem to get it right. With a de-focused star, I can get the donut effect with the centre properly centred. However, when I bring the scope to focus, the stars turn into long streaks with little "star bursts" at each end. Additionally, when focussing, initially, the image in the eyepiece is static but when it gets close to the point of focus, the image in the eyepiece moves up and right and then down and right (with the direction of focus in one continual direction).

Perhaps this means I need to take it to a specialist for service/repair?

Any comments welcome please.

On the up side, I have a new Celestron AVX mount for it and after giving up on the C8 earlier this evening, I put on my 6SE OTA and had a great evening, the AVX mount is excellent (thank you FLO, fantastic service again)

[Charic]

Gazzabone.......Hi There, Unfortunately I don't own a CAT, is anything here of any use? 

ftp://downloads.celestron.com/pub/manuals/telescopes/ultima_series/c-8_multiples.pdf

http://www.asterism.org/tutorials/tut14-1.htm

[Gazabone]

Gazzabone.......Hi There, Unfortunately I don't own a CAT, is anything here of any use? 

ftp://downloads.celestron.com/pub/manuals/telescopes/ultima_series/c-8_multiples.pdf

http://www.asterism.org/tutorials/tut14-1.htm

Many thanks Charic, I'll give that a try next time there's a reasonably clear night, it looks like identifying collomination is more precise than I thought!

Cheers

[ronin]

If you do decide to have it repaied then I fell over this a couple of days back:

http://sctelescopes.com/

[Gazabone]

Thank you, looks like a good service so will give it a try if my next attempt at doing it myself is no more successful than my last attempt.

Many thanks

[CodnorPaul]

Try to re-focus a little in and out after sorting the big donut centering, will give more fine collimation. And if you don't have them get bobs knob's - you can look through the EP and reach them on a C8 so get a livetime idea of what you are doing without risking the corrector with a screwdriver!

[CodnorPaul]

Sorry also star bursts at each end doesn't sound right - you haven't overtightened the screws have you so it is distorting the secondary?