How much magnification?

Glen of Okinawa, Japan writes:

I really enjoy your blog. Your digiscoped photos are exquisite and set the standard for quality. I have just started digiscoping and understand that there is quite a learning curve with this technique. I have a Swarovski ATS 80mm HD spotting scope with 45x wide-angle eyepiece and Canon A95 digital camera. My photos do not have the razor sharp detail and focus that yours do. While I really love the 45x eyepiece for birding I think it may be a bit too powerful to produce high quality digiscoped images. Do you agree? What eyepiece power do you take most of your images with? Which power gives you the best quality? I am considering purchasing a 20x or 30x fixed or 20x - 60x zoom eyepiece in the hopes of obtaining better quality digital images. Do you think there would be much of a discernible difference in the image quality produced using a 20x or 30x fixed versus the zoom at a corresponding power?

My reply:

Nearly all of the digiscoped images on my website were taken at 20X via the 20-60X zoom eyepiece and around 1.5 to 2.5x optical zoom on the digital camera. The goal is to achieve a fast enough shutter speed (1/125th of a second or faster) to get sharp results, but increasing the eyepiece magnification will slow things down (less light) and probably result in blurry images. I think 20X is plenty of magnification on the eyepiece in order to work with subjects from 30 to 50 feet (passerines) and for larger birds you can be 100 feet away for composition (waders, small raptors & owls, etc.). I think the tendency for new digiscopers is to crank up the magnification in order to be further away from the birds, but your results will suffer.

If you're going for portraiture, stick with 20X and just enough optical zoom on the digital camera to eliminate vignetting. Then vary your distance to the bird for composition. As for image quality using fixed 20X versus zoom 20X, the difference will be negligible. Again, all the images on my website were taken through a Swarovski 20-60x zoom eyepiece. Although digiscoping affords being further away from birds, you still need to be fairly close to them if your aim is to capture intense detail.

(click on either image for larger version)

Testing zoom against fixed has been done before, but here are my results. On the left (or top), the Swarovski AT/ST 20-60X zoom set at 30X. On the right (or bottom), the Swarovski AT/ST 30X WA eyepiece. You can see that the image taken with the fixed is only slightly brighter (but its background is darker) and perhaps just a smidge sharper. I let the camera spot-focus/timer on the bird's eye. Images were 50% resized, cropped with no level or color modifications - EXIF data included on each image.

You might also want to review my focusing technique.

Have a digiscoping question? Feel free to submit them to me at mmcdowell@tds.net

Digiscoping image © 2005 Michael Allen McDowell