Doughnut stars

[Cloudwatcher]

Whilst checking some recent images taken with the 350D I noticed a number of strange looking stars appearing. The camera was not attached to a scope,doing some widefield stuff,and involved short exposure times at ISO800.

The attached is a crop from a 100% full size image as downloaded from the camera and you can see that some of the stars appear as 'O' rings or doughnuts.

Any ideas what might cause this?

Cheers

CW

(click for bigger doughnuts)

[blinky]

Looks to me like the camera is not focussed.

[Ant]

Yep I agree - that is EXACTLY what I get if the camera is slightly off on the focus!

Ant

[barkis]

Have to agree with the previous suggestions CW. Even the bright stars have a black dot in the centre.

I gather your ZigView can't show up even a bright star. If you could zoom on even one bright one, you might detect this before you expose.

Manual focusing on stars with my camera is a headache. If I don't wear my glasses, I am out a mile.

[Cloudwatcher]

Thanks guys.

I thought it was a focus problem but it's good to get other opinions and to know that human error is to blame rather than an equipment fault.

Cheers

CW

[supernova]

Looks to me like a lot of smoke rings.

[Talitha]

Was there any dew on the lens?

[Cloudwatcher]

Looks to me like a lot of smoke rings.

I do smoke rings,SN but you need 'special' baccy for the multicolour ones,if you know what I mean!

CW

Was there any dew on the lens?

Never thought of that,Carol! Possible I suppose as they do look a bit like condensation. Quite pretty in close up. Might start a new astro art form!

CW