Off axis guider position

[edjrgibbs]

Probably a dumb question but where does the OAG in the image train?

1. Scope - filter wheel - OAG - CCD

or

2. Scope - OAG - filter wheel - CCD

Thanks

[vlaiv]

I use it in position number 2.

Provided you can bring it to focus (depends on OAG and extensions used for guide cam), you will probably want unfiltered light for guiding.

If your filter wheel uses too much of light path and CCD sensor is further (sunken into cam body), you will probably want some kind of T2 extender for OAG guide port (but even then you might have trouble reaching focus then go for option number 1) - just check the back focus specs for filter wheel, camera and OAG and check the math.

[Joel Shepherd]

Yup. Put the OAG on the light path before the filters (#2). Particularly if you decide to do narrowband, you'll appreciate having unfiltered light to guide from.

[edjrgibbs]

Brilliant, thanks.