I've been using my Pentax Optio A10 for several months now behind my Kowa 663 spotting scope and could not be happier. The interesting thing about this setup is that I use no adapter to attach the camera to the scope. When I see something I want to shoot, I just pull out the A10, hold it over the scope and fire away. How is this possible?
The A10 is one of the new breed of tiny digitals that incorporate image stabilization. Handholding at 1x to 3x optical is quite effective and as long as I don't rock the scope in the process, I get images as sharp as if I had used an adapter. There are certainly other brands of image stabilized digitals that will work, of course, but image stabilization is the key if you want to leave the adapters at home.
This technique works especially well for me since I am constantly changing from taking pics through my scope to taking close-ups of flowers and insects. This little camera gives me the freedom to do both without the need for adapters and for that I am grateful. Did I mention that it also takes great pics!
The top pic is a butterfly, taken with a 20x WA TSE-21WD, through the spotting scope and 2x optical on the camera.
Below it is a Great Egret framed nicely with two Mallards at its feet, taken at 40x with a TSE Z9B zoom eyepiece on the spotting scope and 2x optical on the camera,