The Celestron SkyMaster 15 x 70.

A Work Commenced October 14 2022

Though the Celestron SkyMaster 15 x 70 was introduced a few decades ago, several clones of this highly successful product have come and gone over the years. Indeed, back in my days when I was a professional astronomy writer and telescope reviewer, I briefly got caught up in the new fad of using cheap clones of the Celestron offered by Revelation Astro, for example, which I bought in and briefly played around with. I do remember one unit arriving out of collimation, while the other delivered only so-so images that simply didn’t engage me. You see, I just had no enduring interest in binoculars for much of my early career. But how times have changed!

In preparing for the writing of my book, I decided to buy in the latest rendition of this binocular for a fresh look. I was quite impressed by the package and the build quality of the instrument, especially when you factor in the very modest cost of this big binocular – of the order of £85. The instrument is covered with a durable black rubber armouring that affords excellent grip when hand-held.  While it’s unquestionably a large binocular, it’s not all that heavy. My sample tipped the scales at 1251g, so quite light for this configuration.

Optics

During the day, the SkyMaster 15 x 70 produced bright and sharp images, with surprisingly good contrast. I could instantly see how it’s so popular as a long-range optic, for studying targets in the far distance. Indeed, I can see it serving well as an alternative to a low power spotting ‘scope. Collimation was perfect – unlike what I’d seen on some of the Revelation clones I had used in the past – and close focus was measured to be about 15.5 yards. The central focus wheel is covered in textured rubber and rotates very smoothly with no free play or backlash. The dioptre adjustment is located under the right eyepiece. It moves with a fair amount of friction, ensuring it won’t wander easily during ordinary use.

The large central focus wheel moves smoothly without any free play.

The large achromatic doublet objective has immaculately applied multi-coatings contributing to the bright image and high contrast views. This is undoubtedly helped by the longer than average focal length of the objectives on this instrument – 280mm  – making it a solid f/4 relative aperture. The SkyMaster has a big sweet spot in the centre of the image but does show significant softening at the edges of the field, mostly in the form of field curvature. Of course, a large light cup like this really shines under a clear, dark sky. To get the best use out of it, it needs to be stabilised on a monopod or lightweight tripod. The package I received also included a decent quality tripod adapter to get you started, but a quick rap test introduced too much vibration in the mounted instrument which took quite a few seconds to dampen down, so I’d strongly encourage folk to invest in a higher quality unit, made out of machined metal rather than the hard plastic unit supplied with the binocular.

A big bino like this really benefits from a good, sturdy tripod or monopod.

Examining the exit pupils of the instrument, I was delighted to see that they were round and untruncated, as you can see below.

The left exit pupil.

The right exit pupil.

When I directed a bright light through the ocular lens and measured the size of the resulting disk projected onto a flat surface, I measured its diameter to be about 63mm. That didn’t come as a big surprise though, as these budget instruments are known to have stopped down optics. I did not however consider this to be a serious handicap though, as the instrument still lets through a large amount of light. In another test, I looked for ghosting and internal reflections by turning the SkyMaster 15 x 70 on a bright sodium streetlamp in the distance. I did detect some minor reflections, but they weren’t that prominent based on what I had already seen in some other instruments I’ve tested – sometimes costing significantly more.

Those big objective lenses gather a surprising amount of light.

Star testing on bright stars showed that the inner 50 per cent of the field shows very nicely focused stars, but as one moves further out, the effects of field curvature, astigmatism and coma gradually increase. The outer 20 per cent of the field is pretty much unusable, but that’s a small trade off considering what the binocular can show in the middle of its wide, 4.4 degree field of view.

Let me elaborate.

Views of the Moon are spectacular in the Celestron SkyMaster 15 x 70. Its intensely bright silvery surface is tack sharp in the centre of the field, with excellent contrast. A very minor amount of chromatic aberration could sometimes be glimpsed at the centre of the field, but I found that it was very sensitive to eye placement. Internal reflections were very minor and weren’t in the least bit intrusive on this bright celestial target. The vast crater fields of the southern highlands were beautifully rendered, as were the mountain ranges and ray craters peppering its ancient and battered surface. This will be an excellent instrument for observing earthshine on the crescent Moon when it’s particularly prominent during the months of March and April.

With a steady view, I was thrilled to be able to make out the tiny globe of Saturn, as well as its magnificent ring system. Jupiter can also be glimpsed as a tiny globe together with its four large Galilean moons. Try as I may though, I was unable to glean any details form its oblate disk. At this low magnification – from a telescopic perspective at least – the giant planet is simply too bright to resolve any surface details. However, you can watch the satellites change from hour to hour and from day to day.

The very generous field of view is perfect for framing large open clusters. The Pleiades is stunning through this large binocular, as is the Double Cluster in Perseus and the Beehive Cluster in Cancer. Following the sky south of Albireo(Beta Cygni), the Celestron SkyMaster 15 x 70 served up an excellent view of the Coathanger asterism. I enjoyed a spellbinding view of the Sword handle in Orion  in the wee small hours of a chilly October night, the sheer brilliance of the belt stars and the great Orion Nebula beneath them presenting a very compelling binocular portal. From a good, dark rural sky, stars of at least the 10th magnitude of glory can easily be made out.

Another great use of this 15 x 70 is white light solar observing. The 15x magnification provides a very decent-sized solar disk to allow you to clearly see any sunspots present on its surface. I’ve used my own home-made filters fashioned from a sheet of Baader Astrosolar material, placing them over the large 70mm objectives to get excellent views of our life-giving star.

Conclusions

In summary, for the modest price paid for this binocular, the Celestron SkyMaster 15 x 70, certainly represents great value for money. Some critics have noted that many of these units get whacked out of collimation all too easily. Fortunately, re-collimating this instrument is relatively straightforward, using a simple screwdriver to turn two screws (one for vertical movement and the other for horizontal adjustments) which are easily accessed under the rubber armouring of the binocular. You can find several YouTube presentations to see how it’s done. Doubtless, a savvy and resourceful individual can achieve a great deal with this economically priced instrument, whether it be deep sky observing, comet hunting, solar observing or studying a bird’s nest from afar. It’s simply imagination limited!

Neil English’s new book, Choosing and Using Binoculars: a Guide for Stargazers, Birders and Nature Enthusiasts, hits the shops in late 2023.

De Fideli.