C8 Mirror Lock Screws.... Help!

[tony4563]

OK.. I've just purchased a Celestron C8 XLT OTA. ( Was thinking about buying an SCT/Mak at a later date but this came along and I got it for a great price compared to a new one) The seller says its only been used once and looking at its condition I believe him. Used it properly for the first time yesterday but found collimating it pretty difficult and frustrating (Bought some Bobs Knobs to replace the screws) as the tiniest turn loses the object (in my case, Polaris) from view. I was constantly turning and adjusting to get it right. Eventually I did and the views I got were very nice, however I don't think I let it cool down long enough as there seemed to be thermal plumes spoiling my diffraction ring testing. Anyway, it came with no instructions but I managed to get some from the Celestron website. On reading the instructions I came across this:

" Note... Before turning the focus knob, remember to loosen the two mirror locking knobs located on the rear cell of the telescope. These knobs connect a screw to the primary mirror mounting plate and prevent the mirror from moving when locked down. These screws should be locked down when transporting the scope "

Which screws are these? There are 3 small screws that attach the focusser to the rear cell... I don't think it's them...and thats it! There are two black screws just to the right of the finderscope. Could that be them? If they are, how loose should they be? The scope still seems to focus with them screwed all the way down.

Can any C8 owners (I know there are a few) enlighten me about this?

[John]

Well I'm new to C8 ownership and mine is a 1994 model but, apart from the 3 screws holding the focusser knob in place I can't see any other screws / nuts on the rear cell of the OTA at all. Maybe it's an error in the instructions or they apply to a different model of SCT

Incidentally I had the same fun with collimation - mine was way out at 1st light and it took about 30mins of fiddling to get it to an acceptable state. I don't have Bob's Knobs fitted yet but will soon !. I found the scope needed at least 45 mins to reach ambient temperature and during that time the out of focus star image that I was using for collimation showed a distinct heat plume. Once I'd finished fiddling though the views of Saturn were very satisfying though so it was well worth the effort and I think I can improve on the collimation further in due course. From now on I'm also going to allow an hour for cool down as well.

John

[DOCCORTEX]

These instructions apply to the EDGE version. Standard C8's do not have mirror lock.

 

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