The Kowa TSN-VA3 is a cutting edge improvement in the world of digiscoping products, something for the rest of the industry to envy and quickly emulate. It practically makes shooting with an SLR alone with telephoto lens moot.
The TSN-VA3 is a big chunk of glass and metal that attaches to your TSN-88* or TSN-77* series spotting scope just like an eyepiece. You could actually observe with it right then, as a 14x lens, but it is intended that you attach a Kowa TSN-AR* adapter ring to the rear which matches the filter threads on whatever you're putting behind the TSN-VA3.
And there lies the beauty; because the collimated light optical field behind the TSN-VA3 is so wide and with such abundant eye relief, you're not limited to point and shoots or video cameras to put in the optical path-you can use an SLR with lens!
The TSN-VA3 will allow you to use your SLR camera with its attached lens, and most would choose either a standard fast 50mm lens or a short telephoto such as an 85mm f/1.8 or 100mm f/2.0, etc. Your SLR lens doesn't do the focusing, so if you're buying a lens just for this task don't consider the focusing speed as it relates to digiscoping; all that matters is the optical quality, maximum aperture, and peripheral brightness at maximum aperture. With a maximum clear light-gathering aperture of 88mm and the potential to capture that light at f/2.0 or f/1.4, the TSN-VA3 with TSN-88* scopes presents a serious competitor to a 600mm f/4, 500mm f/4, or 400mm f/2.8 lens so favored today in professional birding imaging.
All ventures in the world of digiscoping require the use of a sturdy tripod, first and foremost. You must take great care to keep vibrations during exposure to an absolute minimum. Adding vibration suppression pads below your tripod will increase your chances of success, and employing a cable release, electronic release, or remote control for tripping the shutter is absolutely necessary.