For no more than the price of a single 4” economy telescope, the Celestron 25x100mm SkyMaster binocular gives you the light gathering capacity of two 4” rich field refractors – 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. With its immense light grasp, 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.
The Celestron 25x100 has a good 3 degree field of view and excellent resolution, so it excels at capturing large nebulas like the Lagoon and the Veil, scanning the Great Galaxy in Andromeda or M33 in Triangulum, taking in open clusters like the Beehive and the Wild Duck, and more. It is waterproof, something rarely found in a binocular in this aperture and price range. That means you don’t have to worry about damaging the binocular if you set it down in dew-soaked grass or a puddle after observing. It has a pebble grain finish that provides a sure grip if it gets wet.
A reinforcing bar runs from the prism housings to the objective lenses. In addition to providing structural rigidity that keeps the optics firmly collimated, the bar provides a sturdy support for the integrated photo tripod adapter. The tripod adapter can slide along the bar to balance the binocular on a 35mm or video 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 such as the one listed below 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. 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 100mm aperture and are unobtrusive for all but the most critical and nitpicky of observers.
The usable eye relief is somewhat limited, at 10mm. This will moderately vignette the image for most eyeglass wearers. Unless you have severe astigmatism, if you wear eyeglasses, you’ll get the most impressive views with your glasses off. Soft rolldown eyecups shield the unaided eye from stray light when rolled up, and cushion eyeglass lenses when rolled down. The SkyMaster eyepieces focus individually, in keeping with its designed use as a strictly long-distance observing tool from a tripod-mounted fixed location.
With a close focus of 80 feet, this is not a general-purpose birding binocular, so fast center focusing is not needed. While you can’t look at warblers close up, the SkyMaster is a good choice for long distance terrestrial viewing under low light conditions. Nesting eagles, deer across a meadow, or ducks across a lake at dusk are prime candidates for this big binocular. As a 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 big Celestron 25 x 100mm SkyMaster is a very worthwhile balance of very big performance versus very sensible price.