Cause of halo artifacts?

[chd]

Can anyone help identify the cause of the halo effects in this image?

It only shows up after pretty extreme stretching of the image, and it looks to me a lot like the effect you get when very de-focused, except that the image itself is pretty much in good focus.

The two vertical lines in the lower part of the halo correspond to the position of two cables from my camera, if that helps.

Thanks!

[chd]

I think I figured this one out, in case anyone is wondering - I think it's a back and forth reflection artifact between the corrector plate and the light pollution filter I was using; solution - don't use the filter when shooting the Pleiades (or other things with very bright stars in them, I imagine).

[ollypenrice]

Yes, this is internal reflection, I'm sure.

Olly

[Earl]

The bright stars in m45 can be a real pain for reflections