[ngcles]

Hi Mike, Rob & All,

Yep, I've got little doubt the big contributor to what you are seeing here is "seeing". The effect is more noticeable on brighter stars than faint ones. The advice offered by Rob is spot-on, particularly about letting the 'scope cool before expecting it to really perform

I'd expect that it will be about 45 mins before the mirror settles down to ambient temperature outside -- so don't expect it to perform well for at least a 1/2 hr, particularly after taking it outside from a warm house to a cold backyard in winter.

If it is well cooled and well collimated it will show nice sharp stars assuming the seeing is good. So called "fast seeing" usually caused by high-altitude, high velocity winds will make bright stars look like tennis balls -- similar to what you are seeing. "Slow seeing" on the other hand will make a relatively good image ripple and wobble about and the cause is likely to be more local or even inside the telescope itself as Rob pointed out. Even a 2 deg C difference between the mirror and the air immediately in front of it will create a rising column of air within the telescope tube which will disturb the image. The only solution is to wait until it stabilises or use a fan to actively cool your primary mirror -- this usually cuts the cooling process in half.

Yes, larger apertures are more "seeing sensitive" than small ones. They look through a larger diameter column of air for a start and because a larger 'scope has inherently better native resolution, it will show up imperfections small 'scopes won't notice.


Best,

Les D