Build Quality of Cometron 7×50
The overall build quality is nice. The binoculars have a soft rubberized surface and feel comfortable in the hand. Two roughened regions on the bottom of the prism casings provide a comfortable grip to place your thumbs, whether you hold the binoculars from the sides or from the front. It is possible to bend the arm holding the eyepiece focus position, but this doesn’t present a problem in general use–just don’t bend the thing. Focus is very smooth. Celestron claims they are “water-resistant” but I’m not getting water anywhere near these things–there are a few places that look like they could let in water through little seams.
Accessories
The Cometron 7x50s include dust caps, a travel bag, and a strap for the binoculars. The travel bag is fine, seems to be made of nylon, closes with velcro, nothing to write home about. Nice for those who will be traveling or hiking with these.
Optics
The Cometron 7x50s use two fully multicoated 50mm objective lenses, two BK7 Porro prisms (I can’t tell if they are coated or not–their reflections are not colorful but they’re also not super bright), and two eyepieces which seem to be three-element Kellners. Kellners have a moderate field of view of around 40 degrees. Given the advertised 6.8 degree field of view and 7x magnification, this is closer to 47.6 degrees. That’s close to Plossl-like performance fields, but I feel that it’s probably closer to 40 or 45 all the same–the apparent field of view does seem somewhat more claustrophobic than a normal Plossl eyepiece in a telescope. The objectives have blackened edges, but the eyepiece’s eye doublets do not, and are easily visible as a stony-white ring inside the eyepiece. Micro-baffles ring the interior of the lens tubes to control stray light.
There is a design flaw in these binoculars, however, that must be pointed out. Like many cheap binoculars, the manufacturer has skimped out on the prisms, and thus the exit pupil is sort of squared-off — implying the effective aperture is cut off slightly. It’s hard to say for sure exactly how much of an impact this has, as it’s not the most severe possible case, but it is something to keep in mind. From a simple test shining a light through the eyepiece and watching the image projected on paper, it seems that images still form outside the “squared off” portion, they’re just dimmer, so I think it must have something to do with the broad light cone and the use of BK7 prisms as opposed to the more expensive BAK4 prisms. More expensive binoculars typically do not have this limitation. The end result is a reduction in effective light gathering and a bit of vignetting at the eyepiece’s edges.
Visual Impressions
I first tried the binoculars from my front porch after unboxing them in the afternoon. They are well collimated, with no trouble merging the images in my eyes. There’s something special about the increased depth perception you get from a pair of binoculars–something which only truly applies during terrestrial viewing and not so much at night.
My first attempt at night was about an hour after sunset, before it had gotten really dark yet. I was immediately impressed by the richness of the view compared to almost any other instrument I’ve used. Orion was littered with stars. The belt and sword fit together in the same field of view, and both OB associations looked excellent with the nebula an obvious (though not super well-structured) puff of light in the middle of the sword. The stars were sharp nearly to the edge of the field.
I went up to the Pleiades next, and was presented with the familiar view of the Pleiades in a small telescope–this time with a certain depth to it, with the Pleiades seeming like they were in the foreground of a rich background. The Hyades–the star cluster making up the head of the Bull–was also spectacularly rich.
Later on, I went back out to search for some more open clusters. Messier 36 & 37 or 38 & 36 fit together in the same field–all three don’t quite make it.
I was also able to observe the Double Cluster, which looks more splendid than in any other 50mm optic I own–the 50mm Galileoscope, 8×50 Finderscope, and 12×50 monocular–due to binocular viewing. It was more than just a pair of granulated smudges–it was a fully resolved pair of star clusters. If my neck had let me, I’d have watched them all night.
I was also able to see the Great Galaxy in Andromeda (M31) as a bright smudgy core and an elongated smudgy disk. The satellite galaxies were not visible (though M32 may have been if I could have held it steadier).
During the viewing, it was clear that any problem with the restricted effective aperture melted away, and I was left with a magical and fun viewing experience limited only by my ability to crane my neck up.
The next morning I saw that the last quarter Moon was out, and I took a peek. Even in daylight, craters were obviously visible, and the Moon seemed to hang there in the distance in 3D. 7x isn’t enough to truly appreciate the Moon’s features, but for aesthetic observation alone it sure impressed me.
Is 7x the right magnification?
The Cometrons are sold at the same price point as two of Celestron’s other 50mm binoculars, the UpClose 10x50s, and 20x50s. I wouldn’t be surprised if they were identical except for the eyepieces. 20x50s is almost certainly too much magnification for a handheld optic–you would almost certainly want a tripod or parallelogram mount at that kind of magnification. 10x50s however are a lot more reasonable.
The reason for the name Cometron is that low power, wide fields of view are ideal for searching for dim, fuzzy objects, such as nebulae, galaxies, and solar system comets. However, the lowest power, highest surface brightness is not always the best way to observe faint extended objects. By sacrificing a bit of apparent surface brightness on the object itself, you can get a darker sky background and a larger apparent size, potentially making it easier to see an object, or to resolve detail in it.
To me, the niche of a very low power 50mm binocular like this is not the high surface brightness necessarily, but the incredibly rich fields of view. Higher powers spread out the visible stars and make the views less starry overall.
Also, be aware that a 7×50 optic has an exit pupil of 7mm. If you’re over the age of 30 or so, there’s a good chance your eye pupils won’t open wider than that, and light will be wasted, effectively making the 7x50s into perhaps 7x35s or worse. Check your eye pupil diameter before choosing binoculars.
If you have other telescopes, especially other rich field telescopes such as a Short-Tube 80 or even the Celestron FirstScope 76/300, then I would suggest going for something which will fit a more obviously different niche–that is, go for lower power, richer field.
For terrestrial use, the Cometron binoculars will work fine, however, keep in mind that 7x is fairly low power for terrestrial viewing, and during the day your pupils will be constricted to as small as 2mm, wasting a lot of light. Either smaller aperture 7x binoculars, or larger magnification 50mm binoculars, might suit daytime needs better.
At 7x, you’re not really going to have much luck with planets. It’s not anywhere near enough to suspect Saturn as non-circular, and only the most eagle-eyed observers with a steady tripod have a realistic shot at resolving Jupiter’s moons.
The Moon, of course, looks good in any telescope or binocular, but 7x is nowhere near the maximum useful power of a 50mm optic.
Telescope or Binoculars?
If you’re just starting out with astronomy, and you’re interested in stargazing, deep sky objects, and stars, then you can’t go wrong with a pair of 7x50s (as long as your pupil opens wide enough). However, there are some reasons to prefer even some very cheap telescopes.
The Celestron FirstScope (get the Cometron or Orion FunScope versions, which includes a finder and some decent eyepieces) is not vastly more expensive, gathers about the same amount of light, and has a few advantages. Its tabletop mount allows for stable, sturdy viewing so long as you have a surface to set it on. It can change its magnifications to suit the situation. It is capable of some very rich wide fields. The spherical aberration in the FirstScope’s optics is a problem if you’re into the Moon and Planets, but you wouldn’t get a pair of binoculars for those anyway. However, while the FirstScope’s optics are plenty capable of showing views that are comparable to 50mm binoculars (or better for those cases where higher power is desired), binoculars are more portable, slightly more intuitive, and about half the price.
If you’re into planets and the Moon, then a small telescope (either a long-focus refractor or reflector, or a parabolic short-focus newtonian, like the Orion SkyScanner) will be a much better choice. Just beware of hobbykillers in the sub-$100 price range, which are characterized by false-color-ridden singlet objectives, claims of very high magnifications, bad eyepieces, and worse mounts.