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When recommending digital cameras for digiscoping, I tell people to pay attention to the optical zoom specification (for vignetting reasons) and ignore the digital zoom. However, there is one focusing technique I occasionally use in that employs the digital zoom. It's an effective technique for achieving a sharp focus on stationary birds, such as waders and perched raptors.
Switch the digital camera to infinity focus (this is the mountain icon on Nikon digital cameras). Now all the focusing will be done manually on the spotting scope, but how can you tell if you’re in focus on the tiny LCD monitor? Frame the face of the bird so that it is in the center of the field and zoom the digital camera all the way through the optical zoom and into the top of the digital zoom. The eye generally produces a large, contrasty object to manually focus on. Using the spotting scope's focuser, adjust the focus until the eye appears as sharp as you can possibly get it. Once you're satisfied with the focus, return to the optical zoom and compose your shot. Because the digital zoom has nothing to do with the optics on the camera, the focus will remain true.
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You still have to be quick, because if the bird moves forward or backward even just a little, you’ll have to repeat this sequence. For obvious reasons it doesn't work well on fast moving songbirds, but if you have one that’s preening or keeps returning to a particular perch, you may want to give it a try.
All images © 2007 Mike McDowell