Minox 15x58 FL Review

Fluorite can be an emotive thing in this hobby, which is why you see it used in so much advertising. The time I first came across the big Minox binoculars I was the proud owner of two refractors containing fluorite in their objectives: an FS128 and an FS102. I liked both scopes a great deal, so the idea of a high-power binocular containing the magic mineral appealed.

At that time I had just been getting interested in binocular astronomy beyond casual sweeping and looking at the Moon and the brightest Messier objects. I had realised that I needed more power and bigger objectives to go deeper, but I didn’t want big binos I would have to mount on a tripod: to me the immediacy of hand-held binoculars is what makes them different from dragging out a telescope or opening the dome.

In my opinion 15x magnification is about the very most you can hand-hold without a tripod or image stabilisation. There are very few quality hand-held binoculars made with a 15x magnification, because it is a design that appeals mainly to highly specialised niche markets, like hunters, plane spotters and astronomers. Apart from the Minox, there is a Swarovski 15x56, a Leica 10+15x50 dual-power, both reviewed elsewhere on this site, and that’s about it. Other high-power binoculars tend to be much bigger and not really holdable, or of dubious quality. And of course, being essentially a hunting binocular, the Minox are fully waterproof unlike most big porros.

“But I don’t need waterproof binoculars for astronomy!” you say. Are you sure? One of the things a completely sealed binocular does is to prevent internal fogging during prolonged use in extreme cold, something which could be useful in an astro’ bino’. Then again, I sometimes take binoculars with me to the top of the local fell where there are great views of the Moon and inner planets when low in the sky. On my hour-long trip up the fell, sudden and heavy showers are not exactly unknown. So certainly for me, waterproofing is a nice-to-have, if not absolutely necessary.

The Minox 15x58s are no longer made and even when I bought mine a few years back they were being heavily discounted; nobody wanted them it seems. Mine came ex-display from a dear-stalking outfitters in the Scottish Highlands. I imagined them having sat gathering dust amidst kilts and antlers and bars of Kendal mint cake, whilst the mists rolled past the window in some sleepy Glen. I probably wasn’t far off, because when they arrived, the eyepieces were coated in a film of impacted dust and grime (which was easily removed): they must have been on display for years.

Design and Build

Body and ergonomics

Look and feel of the Minox is distinctly mid-range and Japanese, not premium and German.

The 15x58s are large for a roof prism binocular, arrestingly large and very long in the barrel, so that they look vaguely menacing. They weigh almost 1.5 kg. If you go for a walk with these on a Sunday afternoon, forget blending in with the bino-toting crowds; you won’t, because these look massive and ridiculous hanging around your neck.

First impressions are that they don’t have the elegance of a Leica and the build quality doesn’t feel in the alpha class either, though perfectly acceptable. The black armour looks more like the covering it is, than an integral part of the body the way it does with the best. Plastic parts like the focuser and the eye cups are more... well plasticky than they would be on a Leica. So these are not an especially attractive pair of binoculars. That said, they are clearly well built as they have waterproofness specs equal to the very best and instead of nitrogen purging you get argon purging (argon, being an inert gas, should help prevent internal corrosion). The lens coatings look good too and behind those big lenses (it’s amazing, by the way, how much bigger 58mm looks than 50mm) are a series of ridged baffles machined in to the barrel.

Optics

Of the three 58mm models Minox used to sell, only the 10x and 15x claimed use of Fluorite. I now know that when manufacturers say “Fluorite”, what they often mean is “high fluoride glass”. Does this small deception matter? I believe so, because Fluorite certainly isn’t a glass, it’s a crystalline material; also, fluorite allows a level of correction for chromatic aberration that even high-fluoride glass like FPL53 can’t quite match. Anyway, I have no idea if the Minox contain fluorite or not; finding out involves using a laser (glass scatters the beam and you can see it in the glass, Fluorite doesn’t and you can’t). What is crucial is that in either case, you could expect that these binoculars would be very well corrected for chromatic aberration.

The blurb on the big Minox say that they use aspherical elements in the eye lenses and they contain fewer elements than some premium binos. Even so, they manage a decent field of 4.1 degrees and good eye relief; a flat field is claimed as well. The eyepieces have twist-up eyecups and the right one also has the diopter adjustment on my (early) pair, but later ones integrate it with the central focus knob.

I should say that the Minox looked very similar in some ways to the Nikon Monarchs of the time and I suspect they may have been made under license in the same Japanese factory, despite being a German brand.

In Use - Daytime

Like many high power binos, the Minox are unimpressive under normal daytime conditions: relatively dim, with a narrow field. More troubling is that focusing is rather soft and it’s hard to find the best focus point. To make things worse, the right barrel seems a bit softer than the left as well and is particularly difficult to focus. If that weren’t disappointing enough, the fluorite (or FL glass) does little extra to control chromatic aberration, which is at the level you tend to find in ordinary binoculars, i.e. quite noticeable in high-contrast situations.

Dim, you ask? How can they be dim with 58mm lenses? Here we need to delve into a bit of theory. During daytime, your pupil contracts to just a millimetre or two in size. This effectively stops down any binocular you use so that you are really using 15x30s or whatever. How bright the binos seem under daytime conditions has more to do with the transmissiveness of the lenses and prisms than the objective size. So the Minox probably seemed dim due to relatively ordinary coatings and prism mirrors. So does this mean they are dim at night? No, because then your pupil dilates and you get the full benefit of the big lenses.

In Use – The Night Sky

The Minox were so lacklustre during the day that it was ages before I ventured under the night sky with them. When I did I was mightily surprised. Yes, they are heavy. No, the Moon isn’t as sharp and vivid as in a premium binocular. However, deep sky objects with these are the best I have seen with hand-held binoculars. Finding the Ring Nebula, the Crab and just about any bright globular cluster is easy, as are many of the brighter galaxies. You can see the dumbbell shape of the dumbbell, rather than just a faint fuzz. What with the big objectives and comfortable view, the Minox prove a pleasure to use hunting Messier objects and I have found things with them I haven’t with binos before or since.

Why are these binoculars so good on DSOs? Again, it’s all down to the maths. Light gathering power is proportional to the area of a lens, so 58mm binoculars gather 35% more light than 50mm ones. That’s a very strong argument, which overwhelms any losses from slightly poorer coatings. The Minox worked so well because they were big and had sensibly designed eyepieces, that’s all. And for deep-sky, indifferent cornering doesn’t matter as much as sheer horsepower, if you get the analogy.

From a technical perspective the binoculars perform very well, too. The field is flat as promised and eye relief is excellent. The field is narrow compared to lower power binoculars, but is acceptable at 4.1 degrees and you can easily see the field stop with glasses. These characteristics all sum up to make the view just plain comfortable, as I said before. Ghosting is well controlled if a bright light is placed just outside the field, so the baffling works. The full Moon looks clean, with minimal flare, indicating good coatings and quality glass.

So these binos are great for Messier marathons, but they easily let you keep track of the Galilean moons of Jupiter too and whilst our own Moon isn’t as crisp as in a premium binocular, the high magnification shows a lot of detail that lower powers don’t. Overall, then, night-sky performance is excellent, belying the unimpressive daytime view. Interestingly, using them for long distance viewing of ships in the bay in deep dusk conditions also plays to their strengths, as you might expect.

The biggest drawback for me with these monster binoculars is a combination of weight and shakes. The only way I found to get them under control is to hold them around the barrels, just behind the objectives, resting the eyepieces on my glasses; mostly it’s worth the effort. In fact my observing pal likes them better than any other binocular he has used. I find that I can only hold them for quite short periods, but during those periods, deep sky performance is amazing for a hand-held binocular.

Summary

In the end I sold the big Minox binoculars. I am fussy and don’t like mediocre optics and these were well short of perfect, particularly in the right barrel. They didn’t have any better correction for CA than any other binoculars either, despite the “fluorite” tag. All this meant nothing under the night sky, though, because you could just see so much more with these than even with, for example, Nikon’s 12x50 SEs. The main other problem for me was their weight and bulk. Yet, they were smaller and wider of field than most “astro” binos. Even the 15x50 Leica Duovids didn’t measure up on deep sky, despite having far superior optics in terms of clarity, sharpness and contrast. For deep sky, aperture wins, even in hand-held binoculars.

If you ever stumble across a pair for a sensible price, the big Minox 15x58s are cautiously recommended.