You will never get any lens on that D80 to work for digiscoping IMHO. Digiscoping requires a significantly smaller sensor and lens diameter to work efficiently. I have a Canon G9, T2i and a Panasonic TM700 video camera.
The T2i is not capible of seeing anything out of a spotting scope. The zoom is not far enough on any lens short of a 200mm to see past the "tube" of the spotting scope.
The G9 gets a ring about 1/3rd the size of the frame when zoomed all the way into 6x. It allows you to see the image, but is not very good.
The TM700 needs about 14x zoom to get past the tube and is prettg good when the critters are out about 3/4 of a mile away.
If you want to get good images of critters through your scope you'll need something with 7x zoom and a relatively tiny sensor and lens.
My next purchase will be a Sony WX5 as it does 12megapixel stills and 1080i video but is small enough to capture through the spotter at 1/3 mile out to a mile or so incredibly.
Take a look at www ##### dot com's Point and Shoot Scope)cam setup. It's prefect blend of size quality and ease of use for digiscoping.
I know, we all want to have that incredible image quality we could get from the high end digital slr's, but you'd need a scope the size of the hubble space telescope to get it to work
Cheers,
Pete