Digiscoping Primer--page 2

3) Get a stiffer tripod!

The tripod and head combination that currently supports your scope is probably inadequate for visual use, much less photographic. Does the view through your scope shake in a light breeze? Do you routinely rest your hand on the scope to improve the view? If so, your tripod and head aren't sturdy enough. That's understandable, since sturdier tripods tend to cost and weigh more. Further, human vision (approximately 1/10th as acute as that of the last raptor you saw!) has a remarkable ability to compensate for poor imaging. Alas, your digital camera does not.

For high-magnification photography, the choice of tripod and head ("support") is literally the most important choice you will make. How can that be? That's because the optical quality of most cameras and scopes is quite high; the differences between high end and midrange scopes and cameras are small compared to the averages of their capabilities.

The situation is very different with supports. Tripods and heads are specified by the weight they will support. That's misleading, however. What the manufacturers really should specify is the rigidity against vibration, or sturdiness, of the tripod; but because there are many different camera shapes, and no simple measures of rigidity, they list a weight capacity instead. They further assume that whatever you support will be compact, symmetrical, and balanced over the tripod centerline, as extended objects tend to vibrate more. Obviously, your scope isn't what they have in mind.

Detail with inadequate and adequate scope support

Therefore, the support you use should be vastly overrated for the weight of your equipment. A scope/eyepiece combination (manufacturer specs are usually for the scope body only!) generally weighs about 2 kg. Your tripod should be rated for at least 10 kg (remember that the tripod carries the head too, which alone may be 2 kg), with a similar rating for the head. Choose a head--pan or ball--which locks firmly. Your scope/camera will also be more stable if you spread the tripod legs wide and keep the scope low. (Sit!) Keep the center column down; increase leg extension instead.

Vibration is the enemy in photography, digital or otherwise. You can compensate for low light or subject motion, but if the camera vibrates during the exposure, the image is irreparably smeared. Remember that as you magnify an image in your scope, you also magnify the blurring effect of any vibrations. An inadequate support allows too much vibration, and the most expensive optics can't fix that.

4) Switch to a fixed-magnification (non-zoom) eyepiece

Aside from being one more thing to fiddle with, a zoom lens is a severe optical compromise. No, not in image quality; at the high end, the image through a zoom lens is as crisp and color-correct as that through a fixed eyepiece. The compromise comes with field of view. Field of view--the most valuable optical commodity at high magnification--is usually much larger for a wide angle fixed lens as for the zoom at identical magnification.

Field of view is expressed in two ways: the angular width of the visible field, or the linear width of the field at a given distance. In general, as magnification increases, field of view decreases. In angular terms, the field of view of the Leica zoom eyepiece is 1.9 degrees, or 34 meters at 1000 meters, at the 20x setting; at 60x, 1.2 degrees. (The angular width of the sun or full moon is about 0.5 degrees; of your fist on extended arm, about 5 degrees.) However, the fixed-mag 20x eyepiece has a field of view of 3.45 degrees--nearly twice that of the zoom! So why isn't the zoom made with a larger field of view? It could be, but the eyepiece would be much larger (heavier) and much more expensive. Manufacturers have made the marketing decision to trade zoom capability for field of view.

Click for field comparisons

However, for a birder this is a poor functional trade. High magnification is meaningless if you can't find the bird! And a large field of view makes finding the bird much easier. It can help you follow a moving bird, and even let you see what the bird is so interested in. If you often zoom out so that you can see more of the bird or its surroundings, you need more field of view. Besides, does going to full magnification show you more detail, or just the same detail larger (and darker--image brightness is inversely proportional to magnification)?

For photography, it's important to use as much field of view as possible because the camera's field of view is smaller than that of your eye; through the scope, the camera won't see as much field as you can. For Leica's fixed 32x eyepiece, the field of view is 2.3 degrees; at full camera zoom, the captured image is only 0.7 degrees. Within limits, you can increase the overall field by zooming the camera lens out. But at some point the camera's entrance pupil--the virtual circle, usually the front optic, that limits the camera's field of view--will retract beyond the eye relief of the scope, vignetting the image. Not only does the fixed eyepiece have a wider field for the camera to view, but it also has a longer eye relief; this allows you to zoom out further before vignetting begins. A further benefit is that the Coolpix zoom lens allows larger apertures at smaller focal lengths (wide zoom).

In general, use the smallest magnification that meets your needs--you'll see more and the image will be brighter, giving you much more flexibility with camera controls and image editing.

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