inverted vignetting (1 Viewer)

Hi,
I have try to make some video with my scope this week end, but strangely at wide angle there are no vignetting, but when I crank the zoom of the camcorder vignetting appear close to instantly and disapear again when close to the 20X of the zoom??? so what's the problem?
Canon ZR100 20Xzoom (28mm thread lens)
Nikon 82ED + 30X wide DS eyepiece
Nikon adapter for DS eyepiece (28mm thread)

thanks

I think that this is an effect of the way that camcorders zoom. I have a Sharp camcorder, when using through my scope there in very little vingetting with no zoom and none at 9-10X, but inbetween it is really bad.
I think it occurs because the lens is closest to the front of the camcorder at wide angle and as you zoom, it draws into the body of the camcorder. this moves teh lens further from the eyepeice creating vingetting, which is then overcome by the effect of the zoom. That could of course be total rubbish, no doubt someone who understands the technology will give a proper explaination...

Thanks for the reply,
It's exactly as you describe, and that make sens.