help with vignetting

I'm brand new to this game so please be tolerant.
Here's my digiscope equipment:
Scope: Celestron Ultima 80 ED 20x-60x
Camera: Nikon 40D.

I went into the field and shot 700 pics of a peregrine falcon nesting with 3 fledglings with this combo.
The pics turned out terribly vignetted - I'm not even sure this is the proper term for what I saw.
There was a circular shadow in the centre of the picture which gradually faded towards the edges.

Any suggestions as to what caused this? It's some type of refraction, I presume caused by the scope.
With this particular camera, I had to remove the lens so I could attach the T-ring adapter provided by the scope manufacturer so the only thing had control of was the shutter speed and ISO speed.
Most of the shots were taken at 1/200 shutter speed and 400 ISO.

Can anybody help me?


Thank you.

Hi Chuckhas
I have not used a dslr on a scope yet so i am not sure if i can help .is the camera centered right. the black ring should surround the image and zoom though it. could you try the camera on scope with lens fitted and zoom trough vignetting. I thought when you put the camera on with out the lens it turned it in to a telephoto lens.
I hope you sort it out . Alan

thanks for the response...i'm not sure if what i'm seeing is technically "vignetting". What I see is not "portholling"... I am actually seeing the opposite.
Click the link to see what I mean.
Maybe I am zooming too much with the scope. With my camera set-up I have no other way to focus.
http://picasaweb.google.com/chuckhas/Vignetting/photo#5222295120415573858

Hi Chuckhas
I had a look at your photo i have not had this happen to me. you could email srb-griturn Thay might be able to help.
if you go to http//rascal.gralleryblogs.net you can see my setup and digiscopeing photos. I would like to move up to dslr at some point.
let me no how you get on. Cheers Scooter

I had the same with my sony a 700 it takes a lot of setting up did get some good shots but now use a praktika luxmedia10-x3 compact camera with digiscoping bracket the more you use it the better the photos.
hope this helps