Is anyone using Digiscoping ? what are the pros ans cons of using one compared to using a telephoto lens ?
I'm assuming you are talking about astrophotography?
Pros:
about the only way to capture really distance objects on the cheap
resulting images, when done properly, look very good
Cons:
fixed aperture
good scopes=$$$
not something you can really take with you on a hike
lots of time/effort required for good results
Of course you will also want a tracking mount to eliminate star trails. Lots of adapters available to make it work: brackets to allow for focusing onto the eyepiece image, t-mount adapters to use the scope as a lens, or eyepiece adapters.
If you are talking about land based digiscoping, then I apologize for all the info above which won't apply. Let me ask you this: have you ever used a mirror lens on a camera before? Digiscoping with something like a spotting scope looks worse, IMO, and certainly far worse than an actual lens. But, if you need 1200mm or whatever, scopes can be a cheap way to get it, and oftentimes the only way.