| Celestron’s SkyMaster 20 x 80mm binocular is a surprising performer for such a reasonably priced instrument. A reinforcing bar runs from the prism housings to the objective lenses. In addition to providing structural rigidity that keeps the optics firmly collimated, it provides a sturdy support for the integrated photo tripod adapter. The tripod adapter can slide along the bar to balance the binocular on a tripod, no matter what part of the sky you are viewing. Once you find the correct balance, a large thumbscrew locks the adapter in place. Using the binocular on a tripod is virtually mandatory, as few people will have the wrist strength needed to hold them steady enough for extended hand held use. The supplied lightly padded neck strap is acceptable for occasional use. However, adding a wide heavily padded neck strap would be a comfortable addition if the binocular must be carried extended distances to an observing site. The SkyMaster uses high light transmission BaK-4 prisms and multicoated optics for bright images of faint deep space objects. It offers the equivalent light gathering capacity of two 3.1" rich field refractor telescopes – one for each eye. Using two eyes to observe increases the resolution of small details by as much as 40% over the resolution visible when using only one eye, as you do when looking through a telescope or spotting scope. It offers admirable astronomical viewing on its own, as well as serving as a good wide-field observing complement to the narrower field of a telescope. With a good 3.2 degree field of view, it excels at sweeping the star clouds of Sagittarius, searching out the Great Galaxy in Andromeda, taking in open clusters like the Beehive and the Wild Duck, and more. There is some barrel distortion (straight lines at the edge of the field are curved), and some visible astigmatism and chromatic aberration at the edges of the field. However, these flaws are minor considering the SkyMaster’s aperture and are unobtrusive for all but the most critical and nitpicky of observers. The usable eye relief is quite good, at 15mm, although the image will vignette slightly for most eyeglass wearers. Soft rolldown eyecups shield the unaided eye from stray light when rolled up, and cushion eyeglass lenses when rolled down. The SkyMaster has center focusing, like a conventional binocular, with a diopter adjustment ring on one eyepiece to match the binocular focus to your individual eyesight. With a close focus of 80 feet, it is not a general-purpose birding binocular. That said, the SkyMaster is a good choice for long distance terrestrial viewing under low light conditions. Nesting eagles or ducks across a lake at dusk are prime candidates for this big binocular. As a first serious astronomical observing tool, as a long distance nature study instrument, or as a highly useful companion to take into the field with your telescope at night, the Celestron 20 x 80mm SkyMaster is a very worthwhile balance of performance versus price.
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