C9.25 mirror locking

Hi,

I've got things pretty well set up in the observatory now and have started so do automated imaging but one of the limitations of the CPC 9.25 is now becoming a problem. There is no way to lock the mirror in place. This results in very noticeable out of focus points on ccd images as the scope moves around the sky.

One solution to this would be to get another mount and scope, but creche fees rule that possibility out!

So I'm left with wondering about modifying the scope to lock the mirror. I've a separate focuser screwed into the rear cell to do the actual focussing.

There don't seem to be any modifications out there on how to do this, which is a little surprising as I'd have thought it would be a common enough mod.

Not having opened up the scope it seems like there are two options.

1. Do like the larger scopes do and drill holes in the rear of the scope to screw into the support of the mirror cell.
2. construct some sort of O-ring retainer around the edge of the mirror and put screws in from the side of the ota that will lock the mirror in place.

Has anyone here tried anything like this before?

Hi Al,
Did it come with a locking shipping bolt, if so then you could use that.
Otherwise I'd go with drilling holes in the back of the ota and get some nuts and bolts in there.
You'd probably need someone to weld the threaded nuts to the back of the scope. I'd have them on the inside of the ota if there was room and if you're going to go to this kind of trouble, then I'd put in 3 of them in the shape of a triangle.
You'd want the bolts to touch the back of the mirror cell and not the glass for obvious reasons...
I'm sure I saw a page many many years ago of someone who did this to an older meade sct.

Thanks Dave.

Celestron only start the shipping bolts with the C11. But that's exactly what I'm thinking of putting in. Guess I'll have to just take it apart and see what's back there to screw into - not the glass anyway

Actually this is more what I was thinking of. Might be a bit safer, and doesn't assume there is a nice plate to screw into behind the mirror and I'm less likely to mess up collimation.

page 5-8 www.marsastro.org/presentations/MARS_Mirror-Lock.pdf

If there is enough space in the 9.25 to do it...

It's a clever idea, but this could knock out the collimation as easily as using the 3screws from behind, I think either system would be ok so long as you don't over tighten the bolts.
Would you have less focusability/travel using this system compared to the 3bolts from behind the cell ?

Just had a thought, I might go for the side bolts as bolts on the back might get in the way of a camera or be more difficult to get to cos of the camera