|
I think the main benefit of an OAG is to avoid flexure issues between the guiding scope and the imaging scope. Usually the heavier the optics the better off you are with an OAG.
If you use an SCT you're best using an OAG. I you use a big refractor as a guider then you're likely to get flexure when weight shifts in various parts of the sky. If you use an small light finder then it's less likely. But as it is separate from your imaging scope, again the primary mirror of your scope might shift, or the tube rings/dovetail flex, so you're better off with an OAG again.
I was getting flexure with my 8" F/4 newt because I had the finder/guider mounted on the tube rings, not on the scope body. Mounting the socket on the tube sorted that out. The scope was moving in the tube rings and that wasn't long FL at all at 800mm but noticeable in the images as a drift that wasn't guided out. An OAG will guide that out.
|