Celestron CPC 9.25" collimation

[Chris P]

Hello all,


I need some help with collimation of this scope. First some
background. I bought a Hotech laser collimation device a few months
ago and this is where it all went wrong. I made a mistake by not
thoroughly reading the instructions and I actually got my secondary
out of alignment. Since then I have managed to just make things
worse. I tried last night for three hours to get the secondary mirror
in alignment but all I could get was a out of center view of a non-
focused star. I can see a double circle. An out-of-focus star looks
like an egg x-ray with the yolk all the way at one end of an oblong
shape. The mirror shadow looks more like two circles halfway across
each other. I tried backing all the collimation screws out to a loose
starting point and had no luck with that either. I ordered some Bob's
knobs so I can stop messing with screws to collimate but I still don't
understand why I can't even get the mirror shadow to move even close
to the center. Has anyone experienced this at all or something
similar? Any ideas? Thanks.

[suthers]

Collimation of a Schmidt-Cassegrain's secondary is supposed to be
possible although I have no personal experience of doing this. There
is some advice here: http://legault.club.fr/collim.html but if it is
wildly out of alignment, you might need to seek the help of a
Celestron dealer. I'd be interested to see what Robin thinks.

Paul

[Robin Scagell]

Hi Chris,

I asked Dave Tyler, an expert planetary photographer, about this and he replied:

"First he simply needs to look through the empty focuser in daylight and get his eye in the middle of the secondary. Next step, try it on a star in very small steps on low power. Next try on a mag of about 200x. When that's OK increase the power to 300x. At these mags an 1/8 turn of a screw may be too much.Seeing needs to be good too. Always check the collimation each time you use the scope , preferably on a star close by to the planet you intend viewing."

I find that when something is wrong with a scope it always helps to begin just by looking through in daylight, as Dave suggests. You can often sort out gross errors in this way as they are much more obvious when you can see what is happening. I'm not sure that it's a good idea to slacken the screws too kuch, BTW -- there may be a danger that the secondary will drop off altogether.

Let us know how you get on.

Robin Scagell