Typically, there are two options:
- Combining a spotting scope with a digital SLR camera body. This costs thousands of pounds, and sometimes means you can't use the spotting scope alone.
- Combining a spotting scope with a standard digital camera via a dedicated adaptor. Again, there is cost involved - most adapters cost several tens of relevant currency units.
Step 1: What You Need
Myself, I am using an old Opticron HR80 straight-through spotting scope (second hand, after my dad updated to Swarovski optics, flash devil), and a "Trust" webcam, which I bought because I thought I ought, and never used.
The attachment is merely a pair of rubber bands, knotted in a particular way, with an optional modifier made of a piece of card.
Step 2: The Highly Technical Mounting Step.
One band goes around the eye-piece, far enough back to be out of the way, and behind something that will stop it sliding towards the webcam. Be careful not to foul your focussing system.
The second band is cut to form a single straight piece, which you tie at each side of the first band.
If your scope has a rubber eye-cup, make sure it is folded out.
Place the webcam against the eyepiece, then loop the cut band over the cam to hold it in place.
Step 3: Adjustments
If you cannot bring your image into focus (say, because your webcam lens projects too far into the eye cup), you may need to add a shim - a small piece of card, maybe a thin piece of wood, with a hole cut in the middle. Slip the shim between the webcam and the eyepiece, to bring the lens closer to the position normally taken by your eye.
Step 4: Go for It!
Granted, it's a bit bulky to carry your laptop to your favourite bird reserve, but if you have a location with a decent hide, or it's a long way down the garden to your bird feeders, then this is the rig for you.
Depending on your webcam's abilities, you should be able to take tolerable-quality videos of birds (or other wildlife), along with digital stills that you can quickly upload to the web as soon as you get anywhere near a wifi signal.
Of course, if you have a small laptop, or an Eeepc, then bulk isn't an issue, and you are set for a life of almost live twitching.