Which OAG?

[JimsShed]

I'm thinking of getting an off-axis guider for use on my c9.25. My current assembly is a Sony a6000 DSLR, connected to a Hotech SCA field flattener, which goes straight into the 2" focus tube.
Like potato chips, I've noticed that you can get them in a thick or a thin variety. Can anyone recommend which type to get, and a brand/model they've had success with.
I'll be using my ZWO185MC as the guide camera.

Thanks, Jim

[billdan]

Gooday Jim,

With a SCT with its generous back focus, you can use either thick or thin.

With a Newt with limited back focus usually this requires a thin OAG especially if a coma corrector is used.

In your situation does the field flattener have to be a fixed distance from the CCD chip like a coma corrector?
This would determine how thick or thin the OAG should be.
You should install the OAG in between the flattener and the CCD chip.

You want the OAG pick up prism as close to the main camera as practical.
Other wise you will need an extension tube to get the guide cam to find focus.


Cheers
Bill