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Home / Celestron SkyMaster 25x100 Binoculars
by Myron Calkins 07/30/03 | Email Author

I was introduced to astronomy at 13 with a 60mm TASCO telescope on a terrible Alt-Az mount. I used that scope consistently and frequently until I discovered girls. Thirty years later, I acquired a nearly identical scope as part of an estate. I cleaned it up and carried it outside into the ice and snow of a New Hampshire winter and was instantly hooked again. Now, 7 years later and living in Tucson, AZ I have three scopes and get out twice or more per week (at least as far as the back yard). I have a superb sample of the Celestron CR-150 (f/8) achromatic refractor on an Orion Atlas mount. I use it with a violet blocking filter for the moon, planets, and doubles. I also have a reasonably good and heavily modified Meade SF-16 dob for deep sky. Finally, I have a wonderful Celestron Ultima 2000 (8 inch) and CCD camera for deep sky photos, comet chasing, and asteroid tracking. What was missing was a low power wide-field grab and go scope for the 5 nights of the week when I have only an hour or so to observe. I bought an ST-80 (80mm f/5) to fill that gap, but it sprouted guide rings and attached itself to the SF-16 as a finder scope.

I was considering something in the way of a 102 f/5 as a grab and go when I saw advertisements for the new generation of 100mm binoculars (Apogee, Celestron, and Oberwerk). At $300-$400, those ads are hard to ignore. Astronomics lists the vital statistics for the Celestron SkyMaster 25x100 as: 100mm objective diameter, 25 power, 4mm exit pupil, and 10mm of useable eye relief. After reading some horror stories about large (80-100mm) binoculars on CloudyNights and elsewhere, I was pleased to read Eugene Artemyeff’s review of the Apogee 25x100s, which I believe are essentially the same binoculars as the Celestron model. I was careful to verify Astronomics 30 day return policy, and ordered the Celestron binoculars from them. My impression reading the reviews was that roughly 50% of the large binoculars got returned for some fault or other. I imagine that not only is it possible to get bad optics, there is the complexity of prisms and prism alignment as well as focus mechanics. In any case, I had high hopes but not particularly high expectations. I should note I have no financial interest in Celestron or Astronomics. The binoculars were purchased at retail, and were not a selected pair.

The binoculars were ordered late Tuesday, shipped Wednesday, and would have arrived Friday, but that was the 4th of July. I waited until Monday for delivery. UPS left the package on my doorstep. They may or may not have rung the bell, my kids swear they didn’t. In any case, the box sat there for a couple of hours in full afternoon sun in Tucson, AZ. When I retrieved them from the sun, the box was very hot and the binoculars were hot to the touch. Discretion is the better part of valor. I re-closed the box and set it aside for three hours to let it cool slowly rather than subjecting the binoculars to the thermal shock of going quickly from 125F to 76F.

That evening I took the binoculars out of their case and got my first chance to look at them. The case is beautiful, zippered, with heavy pads that protect the binoculars well, much nicer than I had expected. Others have said it, and it is true, these binoculars are HEAVY. Hand-holding them is pretty much out of the question for me and probably for anybody else as well. That said, I have hand-held them for terrestrial targets by sitting in an arm chair and slouching down so that I could brace my arms on the arms of the chair. This works moderately well for targets at low elevation, but not at all for higher elevations. I looked around the house for an appropriate tripod and found an old Optex T-70 tripod that was originally purchased to hold a long-deceased VHS camcorder. I remember using the same tripod for the ST-80 before it migrated to the SF-16. This tripod held the ST-80 securely but is marginal for the binoculars.

I installed the binoculars backwards on the mount to get the pan/tilt handle up away from the tripod legs and balanced the binoculars so that the spring in the tilt axis just balanced them when they were horizontal. With the tripod extended to 2/3 height, the setup was stable enough to be safe if watched closely (see picture). Speaking of safe, the ¼-20 screw on the tripod shoe was only long enough to engage about 2 turns into the tripod adapter built into the binoculars. Good enough for testing I said…wrong…when the binoculars broke free, I caught them half way to the floor. Since the screw on the tripod shoe is standard length, others are likely to confront this problem. It is caused by a deep chamfer cut into the bottom of the tripod adapter of the binoculars. A standard length screw on ANY photographic tripod will probably have the same problem, watch out!

With a longer screw and the binoculars securely attached to the tripod, I stopped for a minute to look at them. Fit and finish are good but not excellent. The leather-look textured plastic skin is pretty well trimmed and well glued with no loose edges. The lens cells and rear caps are well machined and well painted with no flaws. Threads on components like the adjustable tripod adapter and the threaded hole by which it attaches to the tripod are very loose but useable. The objectives are beautifully and flawlessly coated. Looking into the objectives, with the setting sun behind me, I saw three mid-green reflections, one upright and two inverted. The one from the front of the objective fades to purple when viewed off axis. Viewed on-axis, these are the ONLY reflections that are visible, there are no others. Moving off axis, there are three more reflections that are brighter and are NOT green. I assume that this is the difference between multi-coated (which Celestron claims the binoculars are) and fully multi-coated which the binoculars clearly are not. The interior of the objective barrels are “threaded” and painted “black” to reduce reflections. The threading is reasonably even, but there are places where the threads are chipped. The “black” paint isn’t very black (see picture) and there are reflections from the threads (more about this later). In fact, looking down the barrel, there are several pieces of metal in the binocular that are painted “not-very-black”.

Looking down the objective barrel with the eyepiece end of the binoculars illuminated, the eyepiece pupils can be seen. When viewed on-axis, the pupils are centered and perfectly round. Moving off-axis at all vignettes the eyepiece pupils immediately. I hope that indicates a well-placed baffle and not the actual edge of the prism. In any case, viewed on-axis, the pupils are un-vignetted. When viewed from the eyepiece end, the exit pupils are round and are about 4mm diameter, as advertised.

So, with the preliminaries out of the way and the sun setting, it was time to take the binoculars outside. Since it was still sunset, I could turn them on the peak of Mt. Lemmon, about 10 miles away. The two independently-focusing eyepieces proved to be stiff, but smooth. Focusing with the two eyepieces is slow but accurate and focus “snaps in” well. With this focus scheme, passing these binoculars back and forth between observers will be slow. On the other hand, the central focus knob is usually one of the weakest links in a pair of cheap binoculars. Celestron has improved reliability simply by leaving out the central focus knob altogether.

The view is wonderfully crisp over the central 3/4 of the FOV, and degrades gracefully beyond. More impressive, the FOV of the left and right eyepieces are identical. As nearly as I could tell, the binoculars were perfectly aligned. A quick look at my back wall confirms that near focus is less than 80 feet, but not much less. Measuring the width of the FOV (41-43) inches and the distance to the wall (75 feet) gives a real field-of-view (RFOV) of 2.61-2.74 degrees on this sample. Not 3 degrees, but close. I measured the apparent field-of-view by setting vertical sticks parallel to the left and right edges of the apparent field of view. The distance between the sticks was 70 inches. The distance from the eyepiece to each of the sticks was 65 inches. Doing the trigonometry gives an AFOV of 65 degrees. At 25x this gives a calculated RFOV of 2.6 degrees, in good agreement with the measured RFOV. It makes sense that the AFOV and RFOV are well matched, the view of my wrought iron fence through the binoculars shows a trace of barrel distortion, but I have to look hard for it. While I was at it I spent a little time watching the Cactus Wrens going about their business. Even the close views are crisp and clear.

Eye relief is adequate, even generous, if you don’t wear glasses. I do wear glasses, but hate wearing them while observing. That’s a good thing because, even with the eyepiece cups rolled down, these binoculars can’t be used with my glasses – period. I have been told that a pair of small round glasses that fit closer to my eyes might solve this problem for both binoculars and scopes. There are also other 100mm binoculars that claim more eye relief for those who must wear glasses while observing.

I left the binoculars outside to stay warm (this is Tucson), had dinner, and returned two hours later. Sadly, it’s July and Orion is long gone but Scorpius, Sagittarius, Lyra, Hercules, and Cygnus are all in nice places. I live north of Tucson, so the southern horizon is pretty light polluted, but overhead, I can see Epsilon Lyrae with ease. Zenith, north, east and west are pretty good. I can see the summer Milky Way starting from a little north of M25 and sweeping to the NE horizon. I also have Jupiter low in the west and roughly a half moon. Jupiter is awful, just bright multicolored mush. What did I expect, looking out at low angle across the hot desert west of Tucson.

The moon is next and is considerably better. The moon snaps in crisply. If I am careful with eye placement, the color correction is pretty good. If I get careless, there are violet and/or yellow bands at the edge of the moon although the terminator remains color-free. As Artemyeff noted with the Apogee 25x100s, these are not APOs, not by a long shot. The color is stronger than my f/5 ST 80. I didn’t buy the binoculars to look at the moon, but less chromatic aberration would have been nice. This is also a good chance to check the RFOV again. It is almost exactly 5 moon-widths. With a moon apparent diameter of 32.6 arc minutes (7-7-03), this gives an RFOV of 2.72 degrees. The view is very crisp except for the last half moon-width (0.25 degrees) at the edge. If I move my eye slightly to concentrate on the edge of the FOV, the view at that edge improves somewhat, leaving only about 0.15 degrees at the extreme outer edge of the FOV that is not focussed well. Working near the moon shows off one of the binoculars’ weak points. The not-very-black “threaded” surfaces in the objective barrels give very bright zebra-stripe reflections in the FOV when the binoculars are pointed near, but not at, the moon. On the positive side, there are no ghost images of the moon when it is in the FOV. In fact, I didn’t see any ghost images of anything at all. Celestron has clearly made good choices about which surfaces to multi-coat.

So, it’s on to Vega. Focus is nice and crisp and I check to be sure that I am right-on focus. What I see out of focus initially looks like a blur, but on closer inspection, it is a tiny diffraction pattern. It is wonderfully round and symmetric. Even better, it looks just like the one on the other side of focus. To my delight, this is repeated in the other eyepiece. These optics seem pretty good. And that is where the fun started. Somewhere between Scorpius and Sagittarius, looking for M7 I remembered why I wanted these binoculars. They give wonderful star-filled views of 2.7 degrees at a time. All those places I have visited with a GoTo scope are suddenly in context with the constellations. I am not just running a computer and then looking in the eyepiece to see M25. I am flying through star fields north of Sagittarius and there it is…M25...and let’s see, yup, there is M24 too. Oh man, when you point these things at the Milky Way, you just get lost in the stars. Up around Cygnus I went hunting for M39 and just never got there. I got sidetracked by all the other stars and stopped caring what I was looking at. For an hour I just wandered around that section of the Milky Way, stopping frequently to smell the flowers.

Summary: So, the big question, am I keeping these binoculars? Yes. They do exactly what I hoped they would. They take me back to the night sky without getting in the way. They don’t need a computer, they don’t need batteries (although one of those motorized binocular chairs…with DSCs…and a PDA running Pocket Sky, and…this is how it always starts). Will the violet and yellow highlights on the moon bother me? Yes. Will the zebra-striped reflections bother me? Yes, until I fix them. Would I rather have Fujinons? Probably. Will I someday buy an AP StarFire because I am obsessive? Yes. So why keep the binoculars? Because they are an excellent sample of remarkably affordable 25 power, 100mm binoculars with a 2.7 degree FOV of which 2.2 degrees are crystal-clear.

My binoculars have six minor defects including: The not-very black paint, three places where the plastic skin could have been better trimmed, and two sets of loose threads (top and bottom) in the built-in tripod mount. But, they have excellent optics are well aligned, the images merge easily and they are FUN to use. If you buy a pair, it will have defects too. Some will be the same as mine (CA and not-very-black paint), some will be different. If they have good optics and you can enjoy them despite their defects, keep them. Notice that I said enjoy them despite defects, not overlook or ignore the defects. Celestron, and probably others, are shipping very affordable binoculars that offer good performance for astronomical use. That is what these binoculars do, they work well for a single observer, at night, pointed at stars (and well away from the moon). They would probably be frustrating at public star parties and they are not really well suited for most terrestrial views although I have enjoyed using them to look at the forest fires on the mountains around Tucson.

To be really fun, they need something other than a tripod. Looking near zenith with a tripod is pretty hard on the neck. I wound up leaning the tripod back into my chair for high-angle views and that was workable, but definitely not a long-term solution. A light simple affordable mount for them is going to be my next project.

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