Basically the concept of digiscoping is adapting a camera to use a spotting scope. You can see this as a variant of doing telescope astrophotography (where you connect a digital camera back or a pocket digital camera to a telescope). Or perhaps it came from the old Eagle Eye OpticZooms that people used to screw into the filter mounts of their pocket digital point and shoots: most notably the infamous swivel-bodied Nikon Collpix 4500 and the Olympus C-*0*0Z series. (I have a friend into astrophotography. The fact that his Olympus C-2020Z was a great camera for digiscoping factored into his purchase and hobby.)
In any case, digiscoping is most commonly used in birding.
I never really thought about digiscoping using SLR cameras. At first glance (comparing how wide the front glass element is, and thinking about the relative magnifications of that vs. a telephoto or telephoto zoom), it would appear that the effective aperture of a spotting scope is going to be really tiny and that resolution is going to be an issue. I’d be thinking a lot of sharpening is in order, sort of like what you do when you “shoot the moon” with your camera:
All these photos have been highly sharpened. Now you might be think these exposure times are short and the apertures are small, but you have to remember the moon is extremely bright: it is a white surface reflecting the sun! Also, the first photo is a crop.
The biggest big-name promoter of digiscoping is Leica. It makes sense because they make the cat’s meow of APO spotting scopes as well as sell a digiscoping kit for cameras like the Leica D-LUX 2 or the Panasonic Lumix DMC-LX1 (essentially the same camera). They have some photos on their site which might give an idea of the typical subject matter and the quality loss of digiscoping.
(I don’t know if it relevant, but the D-LUX 2 is a pocket camera with a 16:9 (2/3″ style sensor, a 35mm frame would be 8/3″ in this metric).
A lot of astrophotographers do use dSLRs for stuff similar to digiscoping (as mentioned above). This explains the short-lived but uber-cool Canon EOS 20Da.
Whenever someone mentions a big telephoto (like in the TechTalk thread), they bring up a picture of the legendary Canon 1200mm f/5.6 L USM lens. It’s that big lens you see in every Canon EOS lens photo
Now since Paul has corrected me, I am surprised that people talk about this lens but nobody gives a nod to the 1200mm-1700mm f/5.6-8s P ED IF Nikkor.
This stuff is just to drool over. They’re both by special order only (I’m told that the Canon 1200mm was discontinued last year) and only movie studios, spy agencies and sport magazines can afford them. Canon and Nikon wheel this glass out for trade shows in order to measure penis size. Sort of like guessing who’ll make the biggest LCD at the latest consumer electronics show.
Bringing this back to digiscoping, people have done digiscoping with even these lenses: video digiscoping. Counting the multiplying effect of a 1/3″ sensor and adding a 2x teleconverter, you have a 35mm equivalent of 17280mm!