Star halo's - A quick question about them

[swag72]

I am getting some halo's on bright stars, which I can live with, but the halo's are not concentric with the star itself - What would that suggest?

Also, when looking at a bright star with a 2 second exposure, the star is not round (A rather lumpy shape!!) - Any ideas on that?

[barkis]

Mishapen stars can be as a result of pinched optics,

The retaining clips situated at 120 degree intervals around the mirrors rim, are intended to prevent it falling out of its cell, should the scope be tipped too far below horizontal. If those clips are pressed tightly against the mirrors edge, it can be sufficient to affect the mirror accurately figured surface. The same applies if there are lateral screws around the edge of the cell, which are used to centre the mirror in its cell.

These effects are quite possible.

Not allowing time for a mirror to come to ambient temperature is also a possibility. Very poor collimation can be a factor too.

Your signature indicates your scopes are refractors, so most of what I've said would be non applicable to you, although temperature changes can affect lens cells, which can cause a pinched lens. Don't forget your eyepieces can affect the image too, if there is a poor quality one being used.

Ron.

[themos]

Depends how the aberrations vary across the image, I guess.