Moving the mirror of a GS for Astrophotography

[1ponders] (Paul) · #1 12-12-2005, 03:41 PM

I've wondered on occasion how far forward the primary mirror of a GS dob OTA (10 or 12") would need to be move to give sufficient focus travel for connecting a 300D. Or any reflector for that matter. Is there a simple formula to work this out?

Orion · #2 12-12-2005, 05:24 PM

I think Scott (tornado33) or Paul (photon collector) can help you out with this one.
I am sure Paul Mayo modified his telescope for his camera.

davidpretorius · #3 12-12-2005, 06:06 PM

46mm i think paul moved his, check his website and his equipment section. I was reading it the other day.

Starkler (Geoff) · #4 12-12-2005, 06:30 PM

How far back in the housing is the ccd in the camera?
The focal plane should be 1/2 inch or so above the focuser when fully racked in so it shouldnt be too hard to work out.

[1ponders] (Paul) · #5 12-12-2005, 06:46 PM

From memory Geoff its 50mm from from the front of the camera (FP?)

Starkler (Geoff) · #6 12-12-2005, 06:51 PM

Paul you should be able to find the focal plane of your scope by holding a tissue or something translucent over your focuser and pointing the scope at the moon.
Take some measurements and you'll know how far your mirror has to come up the tube to bring the focal plane to where you want it.

The downside might be that the secondary is no longer big enough to catch all the light from the primary once you have moved it.