|
Does mirror cooling cause this?
Last night I set up my 12” solid tube dob to do some visual under dark skies while I was imaging. It has been months since I last collimated it, months since it was last used. The mirror clips had been loosened to remove the initial astigmatism that the scope had.
It had 1-1.5 hours to sit and cool a bit but the nights were cooling faster than the mirror could handle without a fan anyway. Collimation looked good but what I did notice when approaching focus is that the star would start to flatten out and bean shape a bit as it approached focus.
Is this caused by a cooling mirror?
I tried it on stars at different elevations but with the same result. Heavily out of focus I could see that the mirror still had some ways to go before the mirror was anywhere near ambient.
|