Troubles with Atik OAG

[sazam91]

Hi everyone,

I began testing the Atik OAG with my WO GTF 102 (has a built-in field flattener) and was having issues with getting the guide camera to focus. I am using a QHY5 L-II autoguider and the Atik 383L + EFW2+ Atik OAG. The CCD camera focuses in at about 48mm and when I attempted to focus the autoguider using the ring on the OAG, I still cant focus it. The only way I can focus it is if if retract the focuser draw tube in which will make my CCD out of focus.

Is there anyone who had issues such as mine and is there a fix for it? I would really like to use an OAG since I am going to be imaging at a longer focal length.

Thanks,
Sal

[Konihlav]

please post some photos of the setup - camera, OAG, how it looks like...

the distance from the pickoff mirror of the OAG to the main CCD camera must be equal to the distance (optical distance) from the pickoff mirror of the OAG to the guide camera...

you can calculate the distance using a scale - measure the physical distance from the OAG mirror (center) to the end of OAG, calculate the distance between OAG and your camera (or FW or whatever) include the backfocus of the main CCD. This number you get means your guide camera's chip must be located this distance from the OAG's pickoff mirror.

You will probably need to either move the guidecam more inside into the OAG or more outside... maybe you can also change the position of the pickoff mirror of the OAG... depends on how the Atik's OAG is built...

I had 4 different OAG units in the past and was able to reach focus with all of the combinations, it's just a game to play :-) and the hardness level depends on how stupid design the OAG has based on manufacturer's brainstorm...

[sazam91]

Hi,

For the Atik 383L the optical back focus is 17.5mm and for the EFW2, the distance is an additional 22mm giving me 39.5mm of distance. And lets ASSUME that the distance from the OAG mirror to the end of the OAG is 14mm. So the total distance is now 39.5mm + 14mm = 53.5mm. So I have to make sure that my Autoguider is 53.5mm away from the mirror using the spacers that come with the OAG, correct?

If so, then my question is this: My Atik focuses (when attached with the OAG, EFW2 and nothing else) when the focuser draw tube is at 48mm out. Having my autoguider at 53.5mm away from the mirror, I will have trouble getting it to focus because I'd need more in focus which would make the Atik out of focus.

What would I do in this case?

I'll post pictures soon.

Thanks!!!!