60, 65, 77, 80, or 88mm?
Though digiscoping has opened the doors of nature photography for thousands of birders and other outdoor enthusiasts, it's still not a "silver bullet" when it comes to obtaining great results. This can be somewhat subjective, as people aren't necessarily seeking a particular level quality when it comes to digiscoping. However, I do feel it's a compliment to digiscoping whenever it is compared, albeit somewhat skeptically and critically, to high-end super-telephoto setups that cost thousands of dollars more. A common question is what effect will a smaller aperture scope have versus a large one when it comes to digiscoping.
Due to a typically large focal ratio (between aperture and focal length), spotting scopes are inherently optically slow even before you attach a camera. Light gathering is crucial when digiscoping. A small aperture spotting scope lets in less light, which directly results in slower shutter speeds, so if you're unable to achieve a shutter speed of at least 1/125th of a second, it will be very difficult to freeze subtle movements of even a perched bird. Low shutter speeds often result in blurry images, one of the most common pitfalls facing both novice and seasoned digiscopers.
Less light being gathered also means an overall decrease in color, contrast, and resolution (nearly 20% when going from a 80mm to a 65mm scope). Post-processing your work with image editing software and tweaking contrast levels, brightness, and sharpness can restore some aspects of this loss. While I've seen exceptional results taken with some of the high-end APO, HD, and ED 60mm to 66mm spotting scopes, I personally recommend 80 millimeters or greater for the best possible digiscoping results.
Smaller aperture spotting scopes are made for a good reason; they're smaller and lighter in weight. Lugging around a large spotting scope and tripod can become burdensome on long hikes, and the relatively nominal lighter weight scopes do seem to make a difference for many individuals, especially those with neck or back problems. It essentially comes down to a question of priorities: are you going to place an emphasis on photography, or would carrying a lighter weight spotting scope benefit your outdoor excursions? It's ultimately up to you, but now you know what the tradeoffs are to make a more informed decision before purchasing a scope.
Read more: Will the smaller 65mm scope fit my needs?
© 2009 Mike McDowell