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Digital camera binoculars: Terms you should know

Current camera binoculars look much like regular H-shaped roof-prism binoculars, with the addition of a camera lens and LCD screen set between the two lens barrels. This means that the distance between the two eyepieces can't be narrowed, if need be, to fit the distance between your eyes -- a source of many complaints we found (and a feature found on most regular binoculars). Also, as with all but SLR cameras, there's a slight difference between what you see through the lens versus what the camera actually captures.

Digital camera binoculars have two sets of specifications and features to understand -- one set for the binoculars, another for the digital camera. The specifications for the binoculars determine how bright and big the image you see through the viewfinder is, and the camera specifications, especially for the sensor resolution, determine how big a print you can make. Storage space varies; the best models include an SD slot so you can take as many shots or videos as your card can hold. Not all digital camera binoculars can take video. The built-in cameras use AA or AAA batteries and upload images to a PC or Mac computer. Most can also play back on a TV screen.

A few budget camera binoculars still use small sensors with a 640-by-480 resolution (VGA),  suitable mainly for emailing and very small prints. Most use 2- or 3-megapixel sensors, and a few current models now provide 5-megapixel resolution. Specifications for resolution can be tricky, however. Reviews warn that some brands, notably Celestron and Meade/Simmons, advertise resolution that's actually interpolated electronically from a sensor that has fewer pixels, resulting in degraded image quality. It's better to compare camera specifications by the actual sensor resolution.

The two numbers in the camera-binocular name -- the magnification and aperture numbers -- refer only to the binoculars, not necessarily to the camera (which oddly enough, may or may not magnify to the same degree). The first number tells you how close you'll be able to see. In a specification of "8 x 32," for example, the "8" means that the binoculars make an object look eight times closer.

The second number -- for example, "32" in an 8 x 32 binocular -- means that the lens furthest from your eyes (called the aperture or objective lens) is 32mm in diameter. For camera binoculars, this varies between about 25mm and 32mm in current models. A larger lens can gather more light so the image is brighter, but the extra weight and bulk make the device less convenient.

Because camera binoculars are designed to photograph distant objects, the minimum camera focus can be quite a long distance. The camera focus is usually fixed, from that distance to infinity. The binoculars, on the other hand, adjust in focus and can usually focus much closer, though the degree of magnification stays fixed. (This takes some adjustment if you're used to zooming in and out with a digital camera.) Also in some budget models, the camera magnifies less than the binoculars.

As you might expect, these differences often result in confusion and disappointment. Often a sharp, clear image in the binoculars is of an object too close for the camera to focus on, so the resulting photo is blurry. Many owners give up quickly, saying the camera binoculars just don't work, but many models get some positive reviews from users who adjusted to the limitations.

Camera shake is another hazard with camera binoculars, because they're harder to hold steady than a regular camera. Most have tripod sockets, and the most favorable reviews seem to come from owners who routinely use a tripod with their camera binoculars. Most users, however, buy this device to minimize what they have to carry, so it's something of a catch-22.

Like regular binoculars, the best camera binoculars use BAK-4 prism glass rather than BAK-7, and they use fully multicoated (FMC) lenses -- several layers of special coatings on both sides of even the internal lenses. Lens coatings minimize the inevitable color distortion and loss of light that occurs when light passes through glass.

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