Canon 10D - Vignetting problem

Anyone know how to trouble shoot the above problem?

attached is a pict of Trffid Neb. 38-30sec stacked exposures at 800iso. the image was stretched, resized, aligned,etc.

Any hints would be helpful
THanks

Attached Image:

Please describe scope and /F ratio.

Did you use a focal reducer?

How did you attach camera to scope?

And yes, I agree it is vignetted.

Alex

You need to flat field divide the image.

This is a simplisitic off the cuff but efffective approach in the absense of real flat field. I hope you dont mind but i tried it with your image.

I use paintshop pro 8.1

I made a copy of the image and gaussian blurred it at about 70%

I inverted the original image and pasted the new gaussian blurred image as a new layer and set the blend mode to multiply and opacity at 50%.

I merged the image and reinverted it.

I readjusted the levels and histgram.

That removed most of the vignetting but left a little uneven illumination.

I made another copy and gaussian blurred it again set at 80%

I inverted the image again and copyed the gaussian blurred image to it and set the blend mode to Dodge and opacity at 50%. I merged the layers and reinverted the image.

That took out most of the vigentting and uneven illumination.

Attached Image:

Perhaps this question would be good to ask on the CCD forum. One of the things I have enjoyed about this forum, is it is film photography related. Sorry if I'm coming across hostile here, but the last time I checked this still is the "film" forum.