Trying to achieve focus with QHY12 CCD @ prime focus

[dylan_odonnell]

Hi all,

I recently acquired my first CCD and had some trouble getting it to focus for first light.

My image train was :

C9.25" SCT -> 6.3 Focal Reducer -> T-adapter -> QHY Clip -> QHY12 CCD

All I was seeing on Nebulosity's "Frame and Focus" was gain noise when I cranked the gain up. Verified it was working by shining light down the tube, that showed up ok. But twiddling the focus knob slowly from one way and then the other showed basically nothing, not even an airy disc. (Admittedly I was on Comet Lovejoy and not a bright star, but there were other stars about it).

Could it be that the focal reducer makes the focal point impossible to reach?

Are there any tips for getting near rough focus from complete darkness when going from the Star Diagonal to the CCD?

Sorry for the silly questions! When I use a DSLR with the same image train I can get focus .. I crank up the ISO in Backyard EOS, twiddle focus to see airy disks then move in from there. Typically about 20 small turns in one direction.

d

[Alchemy]

Distance from t adapter to camera chip will need be the same for both cameras, if the CCD chip is closer (usually) then you can add spacers, Usually focal reducers have a standard ideal distance to the film plane from the reducer. Either side of that will often cause your corner stars to become distorted

[dylan_odonnell]

Thanks I think you are right, the CCD chip does look about an inch closer in the train than the DSLRs inset cmos. I thought the focal reducer might have reduced that focus point but probably not enough.

[tlgerdes]

Also, try starting out by focusing on a bright star like Sirius, it is pretty hard to miss. Then go to something a little dimmer and work your way down to your comet. This way you know things are working fine before scrambling around.