Optics
The SkyMaster 15x70s use 70mm (2.75”) f/4 achromatic objective lenses. Unsurprisingly, these produce a lot of chromatic aberration, but at 15x magnification, you’d be hard-pressed to notice any on all but the brightest targets.
The Porro prisms employed in the SkyMaster 15x70s, as well as with most other good-quality binoculars, are made from BaK-4 crown glass. This surpasses the quality of the more prevalent BK7 prisms found in less expensive or inferior products. BaK-4 prisms are generally crafted to a higher standard than cheap BK7 ones, and binoculars utilising these prisms typically do not have undersized prisms that could cause clipping or vignetting of the field of view. The exit pupils are nearly perfect circles, and the aperture of these binoculars is a genuine 70mm and has not been stopped down internally by a significant amount, with only the slightest clipping around one edge of the exit pupil, not enough to affect views.
For individuals who wear eyeglasses, these binoculars provide ample 18mm eye relief, enabling you to maintain a comfortable distance from your eyes while still experiencing the complete field of view. The true field of these binoculars is 4.4 degrees, which is approximately 9 times the angular diameter of the full Moon. With 15x magnification, this equates to an apparent field of view of 60 degrees, which is quite respectable and fairly immersive. However, the simplistic wide-angle design of the eyepieces combined with the fast f/ratio of the objective lenses inevitably results in some loss of sharpness toward the edges of the field of view. The outer 10-15% of the field is a little fuzzy, but you will probably not notice.
In terms of light-gathering capability, a pair of 70mm binoculars like these are roughly equivalent to a 4-inch telescope. However, unlike a telescope, they cannot provide high-power views of globular clusters, diminutive galaxies, the moon, or planets. Binoculars of this type are primarily suited for observing open clusters and expansive nebulae. There is a decent amount of chromatic aberration with the SkyMaster 15x70s on bright stars, the moon, and the planets, but it doesn’t hamper views in the slightest.
Occasionally, the SkyMaster 15x70s, like many budget binoculars, may arrive miscollimated, resulting in a double image when looking through them. This is common enough to be a serious complaint of ours. Fortunately, Celestron’s customer service is usually able to resolve this issue, or you can access the adjustment screws yourself, though this may prove challenging. Either is time-consuming and can be significantly frustrating, however.
Mechanics
The fold-down eyecups of the SkyMaster 15x70s have a 50mm (2-inch) diameter. The interpupillary distance (IPD) of these binoculars can be adjusted between 56mm and 72mm. Focusing is accomplished using the central knob, while the right eyepiece features a diopter adjustment ranging from -4 to +8 to accommodate vision differences between your left and right eye.
In terms of durability, these binoculars boast a sturdy and well-built construction. While it is always advisable to avoid subjecting them to any kind of impact, they are likely to withstand accidental incidents. However, if they are dropped, collimation might be necessary, which could involve sending them back to Celestron—a potentially inconvenient process – or trying to do it yourself, which requires wrecking the rubber housing to access the tiny collimation screws.
As for mounting the SkyMaster 15x70s on a tripod, forget the supplied adapter. It is all-plastic garbage and induces a lot of wobble, as well as being prone to suddenly snapping under the weight of these binoculars. You can find an aftermarket all-metal adapter for less than $20. As for why they couldn’t include that instead of the supplied one, that is bizarre. Attaching the binoculars to a tripod with a metal adapter is a simple affair—just screw in your tripod’s ¼ 20 screw to the adapter, remove the small Celestron-logo cover on the binoculars, screw the knob on the adapter into the binoculars, and away you go.
Mounting Recommendations
The SkyMaster 15x70s need a tripod or mount of some kind to be used for extended astronomical observation, unless you are built like Arnold Schwarzenegger. If you rest your elbows on something to aim them handheld, you’ll probably be okay for short periods, but that is awkward and limits where you can point them. You’ll also be sure to want a metal tripod adapter to replace the one provided with these binoculars.
When considering a tripod, monopod, or other support for the SkyMaster 15x70s, ensure that it
is capable of supporting the binoculars’ weight. Many readily available or budget-friendly options may not provide sufficient stability or maximum height for comfortable, wobble-free viewing. We’d recommend a monopod or a parallelogram mount, such as one from Orion, for the SkyMaster 15x70s. At 15x, the stability of a monopod, even one without a head equipped, is more than adequate while still allowing for a lot more freedom of movement at a low cost. A parallelogram is an ideal mounting, but it costs more than the SkyMaster 15x70s themselves.
Should I buy Used Celestron Skymaster 15×70 Binoculars?
One of the primary concerns when purchasing used SkyMaster 15x70s or any non-premium binoculars is the potential for them to be out of collimation. It is not advisable to buy a pair that you cannot test in person. Miscollimated binoculars typically display an easily noticeable double image on terrestrial objects at moderate distances, making it simple to identify this issue. Additionally, avoid used binoculars with any signs of fungus or deterioration, particularly if it is on inaccessible interior optical surfaces.
What can you see?
The SkyMaster 15x70s are ideal for stunning views of large open star clusters such as the Pleiades, the Double Cluster, and many others, as well as large asterisms like the Coathanger and nebulae like Orion (M42) and the North America Nebula under suitably dark skies. Globular clusters can be easily spotted with the SkyMaster 15x70s and are distinguishable from stars even at 15x magnification. These binoculars can reveal a few galaxies under dark skies, such as M31 and M33, though urban light pollution may hinder the visibility of fine detail or obscure galaxies altogether. In dark conditions, you may be able to see M31’s dust lane and companion galaxies, as well as hints of M33’s spiral arms. Many of the other brighter Messier and NGC galaxies are visible with the SkyMaster 15x70s in dark or moderately dark skies, including the Virgo Cluster. However, the 15x magnification of these binoculars won’t provide the ability to resolve much detail in these objects, and a 4” aperture equivalent isn’t going to provide a lot of light-gathering ability for galaxy observing anyway.
With their 15x magnification, the SkyMaster 15×70 binoculars allow you to discern Saturn’s largest moon, Titan, observe the various phases of Venus, and effortlessly detect Jupiter’s moons. Some observers can vaguely tell that Saturn has rings – though they appear more like the “ears” in Galileo’s early drawings with his telescope of similar magnification – and you may be able to just barely pick out Jupiter’s striking crimson equatorial cloud belts, but don’t expect it to be easy. The Moon’s larger geological features, including craters and expansive mountain ranges, are also visible with the SkyMaster 15x70s, though chromatic aberration may present a significant annoyance. These binoculars can also separate some of the widest double star pairings, such as Albireo or the two pairs of Epsilon Lyrae. However, a high-quality telescope, even one with less light-gathering capacity, is generally more suitable for examining small and bright targets like the Moon, planets, and double stars, and can reveal the phases of Mercury, intricate details in galaxies and planetary nebulae, the Cassini Division in Saturn’s rings, Jupiter’s Great Red Spot, surface features on Mars, and other things that require magnifications of 30x or greater to really accomplish, a task the SkyMaster 15x70s are of course ill-suited for.
