Atik OAG with Coma Corrector?

[Lex]

Hi folks,

for the moment I am using the TSOAG9; I must admit that I do not want to fiddle around with it anymore. The Atik OAG seems well designed and of a good quality, way better than a lot of the other same price category ones!

My questions is:

Is it possible to use the Atik OAG with a Coma Corr with 55mm backspace? I own the EFW2, the 383l+ and the lodestar as guider. My main scope is a 10" f5 Newt (1250mm FL).
What are the dimensions of the OAG?

Thanks a lot!!

[chrisjbaileyuk]

Had the same issue and no it wont work. EFW is 22mm, OAG is 24mm and CCD backspacing is 17mm so 63mm in all. In addition to get the Lodestar and 383 into co-focus you will need a bit more spacing behind the EFW even with a low profile T-C converter. Add in the various thread converters and it is about 75mm. The OAG/EFW combination is very nice though and works very well. Much better than the TS OAG I intend using with the 460 if the clouds ever part again.

[joelshort]

Chrisj pretty much summed it up, but in my experience it is not necessary to add space between the EFW2 and OAG in order to get a Lodestar to focus.  I use a T to C converter that is about 10mm thick to mount the Lodestar on the OAG.  In addition to having the OAG focuser all the way down toward the prism stalk, you also need to physically move the prism stalk in order to get close to focus.  Doing this gets me very close to focus in the Lodestar, not perfect but perfect focus isn't necessary or even recommended for guiding.  HTH