[Joshua Bunn (Joshua)]

Hi,

Ive been getting my camera chip orthogonal to the optical axis while pointing at the zenith - so far so good (not without many hrs of work under the skies though). When i point to about 30 deg above horizon to see if the focuser has any appreciable flex that shows in images, i get star elongation.

Now,Im using a Hedrick focuser on a CDK with only an stl11000 attached and the focuser is a pretty solid kit. My question is, could this elongation be a result of starlight refraction through the low altitude atmosphere?

The elongation was over the whole chip, all in the same direction, maybe upto 50 - 75% elongation over the round star image. The elongation was always in a direction on my chip which was parallel with a line going from the horizon up to the zenith - no mater what orientation the scope and camera were in.

Thanks
Josh