What's up with this ESO image?

[Karo]

Hi everyone,

I'm looking at Page 7 of the November Sky at Night - the image titled 'Companions in Carina', a wide star-field apparently captured from the ESO in August.

I wonder what's going on here - all of the major stars have a disk around them and on closer inspection, one can see that the disks are offset a little towards the edge of the image. Finally, looking at the two bright blue stars at the bottom right of the image, you can even see the shadow of the secondary mirror and the supports.

You can see the same thing in another of their images, here: http://www.eso.org/gallery/d/104814-4/phot-26a-09-hires.jpg, though less obvious.

The scope in question is a 2.2m f/8 RC. Because of this it seems odd that a it would suffer from this problem at all as a defect of the optics.

Had a quick poke around their pages but no mentions that I could find. My theory is that it's simply an out-of-focus exposure or two which for some reason are stacked in with the others, but I can't fathom why that might be the case.

Any thoughts?