What is digiscoping?

Digiscoping is the practice of shooting digital photos through a spotting scope. The telescope magnifies the subject image for the camera, just as it magnifies the subject image during visual use. The magnification is usually in the range of 20x to 60x for spotting scopes typically used by birders. Most digital cameras have lenses of focal lengths equivalent to 35-115 mm in 35 mm format. The digiscoping combination can therefore result in "35 mm equivalent" focal lengths up to 6900 mm; images shot are magnified 11.5x relative to those shot with a 600 mm telephoto in 35 mm format.

Using a digital camera has many advantages over traditional film photography. However, photography with extremely long focal length lenses presents many challenges. The Digiscoping Primer describes principles and techniques for digiscoping success, and the Image Processing Primer discusses how to handle your images. Look here for a discussion about linking your camera to your scope.

What equipment works for digiscoping?

Two factors determine whether a particular scope/eyepiece will work well for digiscoping with a given camera:

1) Eyepiece eye relief: The camera's front-most optical element-- the first true lens element, not the protective flat or filter--must be held within the eye relief of the eyepiece. That is harder than it sounds because the first true camera lens element is usually quite deeply recessed inside the lens assembly. Therefore, a minimum separation is required between the camera lens and the outer optical surface of the eyepiece. How close is close enough? As close as possible--a couple of mm makes a big difference! If you don't meet this condition you will see "vignetting", a black region surrounding the image field. Check manufacturer specs for eye reliefs, which depend on the eyepiece (and zoom setting for zoom eyepieces) in a non-obvious way. Generally, lower magnification (and higher cost) yields longer eye relief. For a high-end scope eye relief can be as much as 20 mm; digiscoping will be difficult for eye reliefs shorter than 15 mm.

As close as possible!

2) Eyepiece aperture diameter vs camera lens diameter: It is helpful but not essential for the camera lens diameter to be smaller than the eyelens aperture diameter to digiscope. It's not essential because the diameter of a camera lens does not determine the field of view; the diameter simply determines the amount of light passed to the image. (Field of view is defined by the focal length and sensor size.) What a large lens might do is allow light that didn't pass through the scope to enter the camera, causing halos and reducing contrast. If you use a large diameter camera lens, simply mask off the "extra" part of the lens diameter when you mate it to the eyepiece. This will eliminate the stray light that might otherwise degrade the scope's image. (A large diameter lens may also be physically difficult to get sufficiently close to the eyepiece.)

Severe vignetting

First steps: Set your camera to its maximum zoom (and your eyepiece to minimum zoom, if adjustable), hold the camera lens close (!) to the eyepiece, and examine the preview image. If you see a bright round area surrounded by black, the camera's input aperture isn't within the eyepiece eye relief. If you see a bright image filling the preview screen, your gear does meet the eye relief requirement. So now you could either read the Primer, or: find a bright, stationary, high-contrast subject; focus the scope on the subject; set the camera to auto focus and exposure; hold the camera steady; and start shooting!

All Digibird images were acquired using a Nikon Coolpix 990 with a 3.3 megapixel sensor; most images here were taken in 3:2 mode at 2048x1360 size, approximately 200 dpi resolution at 10x8 inches. At screen resolution, 72 dpi, that image is about 28x19 inches. For display in the Digibird galleries, the non-thumbnail images have been resized to about 527x324 pixels at 72 dpi. Image memory has been compressed to about 50 kb. The thumbnails are compressed further, to about 5 kb.

The spotting scope is a 77 mm diameter Leica APO Televid with the magnificent 32x widefield eyepiece. The scope rides an Arca-Swiss B1 ball head with quick-release plate from Really Right Stuff atop a Gitzo 1325 Mountaineer tripod. The camera is hand-held, using a 28-37 mm step-up ring to center the eyepiece and camera.

All images and text copyright 2002 Digibird.com; unauthorized use or reproduction prohibited.

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