Edge distortion is a big problem when digiscoping larger birds such as owls and other birds of prey. One thing that works to the digiscoper's advantage is that, unlike most songbirds, large birds of prey are often stationary. This presents a technical solution that I've found to be effective. Because the sharpest area of the field of view is the middle, I will take one exposure by centering near the bird's face (Image A) before quickly taking another shot of the rest of the bird's body (Image B). These two images are loaded into Adobe Photoshop and carefully stitched together.
Though the process of stitching images together is somewhat tedious, with enough practice you can make your images look seamless:
Depending on the stitch, an added bonus is that the final image's physical print size will be increased. This technique may seem like a lot of effort, but it's pretty easy once you get the hang of it. Remember to think of this when you're in the field and you have a fairly cooperative perched bird that's too large to fit into the sharp-zone of your field of view. Take upper and lower shots and let the magic of Adobe Photoshop do the rest!
Article and photos contributed by Mike McDowell, an avid digiscoper, amateur naturalist, and Eagle Optics employee. Visit Mike's Birding and Digiscoping Blog.