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OAG...AF function+recentering etc

QHYCCD QHY163M Acquisition Guiding Deep Sky Troubleshooting
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Georg N. Nyman avatar
Georg N. Nyman avatar
Hi everyone,

I am tending to move from standard guiding to an OAG system. I tried it yesterday and it worked fine - as long as I did not need to refocus and/or recenter.
But both is during a long night necessary and after doing this, the guiding had either enormous problems or did not work anymore.
My setup ist FL 1500mm, f/8, QHY163m with EFW as main camera and ASI290M as OAG camera.
Did I miss anything? Did I do anything wrong - or do you experience the same issues with OAG?

Thanks for any advise and suggestions!

CS
Georg
Björn Arnold avatar
Björn Arnold avatar
Hi Georg,

Can you give us a bit more detail about the telescope and the OAG used?

I'm also using an OAG and on different telescopes. From 250mm to 2000mm FL. The only problem that I sometimes have is to find guide stars with the 2000mm FL as the field of view is very small and therefore cannot have a sufficiently bright star in the guide cam's field.

As I don't know your specifics, let me give some general recommendation:
1. To setup the OAG, you would focus the main camera through the scopes regular focus mechanism. Once focused, you do not touch the telescope's focus but focus the OAG camera locally (ideally through a small helical focuser). *IF* your filters are homofocal, your guide cam will always be close to focus when your main camera is in focus (I'm quielty assuming your OAG is in front of the filters and doesn't look through filters).

2. If your filters are not homofocal (and OAG in front of filters), it can happen that your OAG is out of focus when your main camera has focused. However, for guiding accuracy it doesn't mean it's all off. Focus is not as critical for the guide cam. Although, you can lose brightness and that can mean that you may have trouble finding a guide star.

3. Is the prism of the OAG behind the filter wheel or in front of it, or in other words, does the guide camera look through the filters? If so, that can be an issue especially with narrowband as too little light will get into the guide cameras.

4. Did something get lose?

Björn
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