[pvelez (Pete)]

I had a further play with my new SBIG 8300.

I took a few shots of the Tarantula a few nights ago. The attached shows the results.

Now ignore the lousy focus and minimal Sidonioing and have a look at the star shapes at the edge of the shot.

I used a Ha filter screwed into the MPCC which was in turn screwed into the 2 inch nosepiece for the camera.

I understand that the MPCC requires 55 mm from focal plane to the MPCC. By my estimate, I have only 31mm to the MPCC ie I'm 24mm short.

So does this explain why I have stars at each corner that seem to be elongated towards the centre of the shot? And if so, will an extra spacer address this?

Just for your info, this is a median stack of 4 x 5 minute shots. Guiding was reasonably solid with PHD.

Any thoughts?

Pete