I find it curious whenever I come across articles that promote digiscoping with 30x or 40x fixed wide-angle eyepieces over 20–60x zoom eyepieces. Many digiscopers concur from the reasonable premise that fixed eyepieces have fewer lens elements than zoom eyepieces, and fewer elements equals less light reflectivity and distortion. Historically speaking, the standard in digiscoping results were set by top digiscopers using their 20–60x zooms at 20x for the bulk of their work—and everyone wants to emulate them.
There’s a tendency for new digiscopers to crank up the magnification because they are far from the birds, but their results suffer tremendously. Therefore, do what you can magnification-wise to achieve a shutter speed that is fast enough for obtaining sharp images.
Less Light = Slower Shutter Speeds = Blurred Images
Nearly all of the digiscoped images on my digiscoping gallery were taken at 20x via the 20–60x zoom eyepiece and around 1.5 to 2.5x optical zoom on the digital camera. I chose the maximum exit pupil of 4mm, which comes from using a 20x eyepiece in my 80mm spotting scope, compared with 2.6mm exit pupil at 30x (even with a fixed eyepiece) and 2mm at 40x.
The goal is to achieve a fast enough shutter speed (at least 1/125th of a second) to get sharp results. Increasing the eyepiece magnification will slow things down (less light), and likely result in blurry images. I find 20x to be more than adequate eyepiece magnification when working with songbirds from 30 to 50 feet away. For larger birds, you can be 100 feet away for composition (waders, small raptors and owls, etc.).
World-class digiscopers obtain incredible sharpness and detail in their images by getting closer to the birds, using the 20–60x zoom at 20x, and using the lowest possible optical zoom on the digital camera that eliminates vignetting. These strategies will offer the greatest flexibility for getting a crisp shot.
For pretty portraiture, composition is an important factor. Lowering the overall magnification and staying at 20x on the zoom eyepiece can mean increased flexibility when composing your subject. Framing an entire bird with a 30x eyepiece may require you to back too far away. In terms of preserving detail, I think it's best to increase the digital camera's optical zoom with a zoom eyepiece at 20x!
Article and photos contributed by Mike McDowell, an avid digiscoper, amateur naturalist, and Eagle Optics employee. Visit Mike's Birding and Digiscoping Blog.