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Tony Flanders
Post Laureate
Reged: 05/18/06
Posts: 3468
Loc: Cambridge, MA, USA
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Last summer I purchased a pair of 12x60 binoculars. Partly, I was rather curious about how they would perform, but I wouldn't have bought them just for that reason. I had a very good excuse in that I was about the fly to the West Coast. I wanted to bring some instrument, and decided near the last moment that a telescope (or more to the point, the tripod to mount it) was too big and heavy. Unfortunately, my 15x70 binos were at my country home, so instead I decided to have 12x60s shipped to my destination in California.
I was a little disappointed when I tested them and discovered that they're actually 12x52s, with the aperture restricted by an internal stop. But then I got to thinking. They really do show a whole lot more than my 10x50s (which are actually 10x46). Proof, lest anyone doubt it, that magnification counts more than aperture. And for the price, the optical quality is really quite good. Moreover, they're reasonably light, and fit my hands and eyes well.
So for a very modest cost, I have a nice pair of 12x52s that are a couple of inches longer, with slightly fatter objectives, than one would expect in 52-m binos. So what?
It may even be that the 60-mm objectives aren't going to waste. When you use an internal stop, different parts of the objective form different parts of the image. This is an old trick to improve flatness and sharpness in wide-angle optics. It is, in fact, the heart and essence of how wide-angle camera lenses work.
Given my 'druthers, of course, I'd rather have true 12x60s. But that got me to wondering who buys 12x60s and 15x70s besides astronomers -- and why. During daytime, most people's pupils open only to 2.5 mm or thereabouts. That means that 12x binoculars are *really* 12x30s, and 15x binos are really 15x38s.
Yes, I'm well aware that an oversize exit pupil is more forgiving of how you center your eyes, and that it's better in twilight, when your pupils start to open up. On the other hand, the difference in weight and bulk between 38-mm and 70-mm objectives is positively gigantic. For daytime use, a 5-mm exit pupil seems truly extravagant once the objectives get to 50 mm.
So who *does* buy 12x60s and 15x70s besides astronomers? Do people buy them because the big objectives look cool, or do they have good reasons? And do they end up happy with their purchases, or do the binos end up sitting in closets?
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Tony Flanders
First and foremost observing love: naked eye.
Second, binoculars.
Last but not least, telescopes.
And I sometimes dabble with cameras.
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Luigi
Post Laureate
Reged: 07/03/07
Posts: 4938
Loc: MA
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For general purpose use, I prefer 8x32s. They're small, lightweight, easy to hold steady for extended periods and with 4mm exit pupils don't give up anything until nighttime. They'll easily fit in the car's glove box or console and are unobtrusive to carry. 8x42s will buy you a few more minutes at dusk and be a little better at night. I currently wear 10x50 Nikon AEs at the scope when observing (on a harness), though have happily used 7x42s and 8x32s for this purpose. I have 16x70 Fujinons and they don't get used except on the rare occasion I haul them out and set up the parallelogram. I'd more likely haul out and set up a telescope. Who buys and uses 60mm and larger bins and for what? I don't know, and if they do, whether their use is really justified.
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17.5" f/5 Dob. IM-715 MCT. 120ED. Lunt 60mm Ha.
Zeiss, Leica, Fujinon, Nikon, Pentax, Bushnell bins
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KennyJ
Reged: 04/27/03
Posts: 12895
Loc: Lancashire UK
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One advantage of buying binoculars with larger objectives than are strictly necessary is the ability it provides to stop down the aperture by simple means of making and fitting aperture masks , which increases the focal ratio and improves the image quality considerably .
When the binoculars are mounted anyway ( which for me I consider essential for all above 10x magnification ) the larger size / increased weight matters not one iota .
In any case , the argument that the eye's pupils being constricted to somewhere in the region of 2.0mm in the daytime makes all the remainder of the binoculars' exit - pupil surplus to requirements , is , I believe , flawed , as it assumes the all the light rays from binoculars enter only the very centre of the eyes , which I don't believe to be the case .
There must be SOME reason , after all , that I can tell instantly the difference between a 3.0mm and a 6.0mm exit - pupil , even in bright daylight .
Kenny
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Tony Flanders
Post Laureate
Reged: 05/18/06
Posts: 3468
Loc: Cambridge, MA, USA
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Quote:
There must be SOME reason , after all , that I can tell instantly the difference between a 3.0mm and a 6.0mm exit - pupil , even in bright daylight.
Interesting point. I was somewhat sceptical about this, so I tried it myself. As it happens, I have borrowed a pair of Fujinon 16x70s and made 50- and 60-mm masks for them for an experiment that I'm doing.
Sure enough, even in broad daylight, it seemed to me that the view got brighter when I removed the 60-mm masks (going from 3.75-mm to 4.4-mm exit pupil) and I was pretty sure about it when I removed the 50-mm masks (3.1-mm exit pupil).
I'm somewhat at a loss for an explanation. One possibility, which is hard to rule out in any experiment involving visual perception, is suggestibility. I don't really have the wherewithal to test this (it would require two identical pairs of binos and a co-conspirator), but I don't think it's right.
Another is that my eye's pupil is bigger than I think. It's pretty hard to measure pupil size accurate to 1 mm even in the best circumstances, and who knows what happens to the pupil when I put my eyes to the binos?
Yet another is that my eyes aren't centered, so my eyes' pupils are vignetting the binoculars' exit pupils. But I spent a while moving my eyes (and the masks) around, and I don't think this is the answer.
Finally, it seemed to me that the brightening was stronger toward the edge of the field than in the center. This would imply that my eyes weren't at the right distance from the eyepieces -- which, given the miserable eye relief on the Fujinons, is quite plausible. In that case, the central light cylinders should be unaffected by the mask, but the ones for the edge of the field would be vignetted by my eye's pupils.
Moreover, it's only in textbooks that there really is an exit pupil at all. In theory, all the light cylinders from points across the eye lens converge on a single circle on a single plane called the exit pupil. In real life, the overlap is never perfect. Again, this would cause the masks to vignette the edge of the FOV but not the center.
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Tony Flanders
First and foremost observing love: naked eye.
Second, binoculars.
Last but not least, telescopes.
And I sometimes dabble with cameras.
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RichD
professor emeritus
Reged: 11/08/07
Posts: 564
Loc: Derbyshire, UK
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Interesting, I have found that it only requires a slight dimming of light levels in a room to make my pupils dilate.I recently measured my pupils as between 7-8mm in a slightly darkened room (bright enough to read the caliper)and even with the main light on, I got 5+mm.
Perhaps even outside during daylight our pupils often reach 3-4mm?
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Clear skies
Rich
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BarrySimon615
Pooh-Bah
Reged: 03/01/04
Posts: 1279
Loc: New Orleans, LA
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Quote:
Who buys and uses 60mm and larger bins and for what? I don't know, and if they do, whether their use is really justified.
Like you, I have a pair of the Fujinon FMT-SX 16x70's, and yes, they do not get used as much as some of the smaller stuff. However I do not consider them daytime use binoculars and that is where the smaller stuff is used more often. When I use binoculars on the night sky, time is split pretty much equally between the 10x50's, 16x70's and 20x100 Miyauchi's. Now to answer your speculation as to who buys and uses binoculars 60 mm and larger and for what? I do. In fact, if I could have only one binocular for night-time use, it would be the 20x100 Miyauchi's, primarily because they push observing with two eyes to a new level and their use on a tripod and with 45 degree angled eyepieces extends observing sessions with binoculars from minutes to hours.
Try a good pair of large binoculars equivalent to (or better) that the Miyauchi 100's, you will love them.
Barry Simon
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brocknroller
Carpal Tunnel
Reged: 10/16/03
Posts: 1947
Loc: Vallée des nuages
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Quote:
....
So who *does* buy 12x60s and 15x70s besides astronomers? Do people buy them because the big objectives look cool, or do they have good reasons? And do they end up happy with their purchases, or do the binos end up sitting in closets?
Tony,
Hunters:
Fuji 15x60 HB @ GunBroker.com
Here's a quote: "You can judge an animal from long ways with 15s on a tripod." from this thread on "Big Eyes or a Spotter":
24hrcampsite.com
And this column comparing larger aperture 12x and 15x bins for hunting.
BIG EYES: Seeing is Believing
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B'rock, son of Grilka
Member of the House of Kozak
Klingon Poet-Warrior
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"The character of a Klingon poet-warrior is measured not only by the metal of his blade--but also by the mettle of his words."
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F.Meiresonne
Post Laureate
Reged: 12/22/03
Posts: 3367
Loc: Eeklo,Belgium
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I have a bino with internal stops. A 10x60 that's actually more a 10x52/53...
but this is a bino with a very sharp field , almost to the edge. Peculiar, actually and that's THE only reason i bought it. It's worth it to me and serves it's purpose.
Of course i knew this all on beforehand. Maybe a buyer who is not aware of it may be not so pleased when he or she finds out afterwards....
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Freddy Meiresonne
Obsession 18 inch #1638
Orion Optics 8 inch F/4.5 -1/8 wave optics -Vixen GP-E
20x80 Helios Stellar Binos
15x70 TS Marine (=Obie Ultra)
10x60 Helios Quantum 4(= Obie Mariner)
10x50 Helios Nature sport plus
8x40 Helios Nature sport plus
Eyepieces in use :Pan 35,24,19, N13T6, Pentax 10 XW, N9T6, Ultrascopic 7.5, TV2, baader ortho 12.5 and 9 mm
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EdZ
Professor EdZ
Reged: 02/15/02
Posts: 14731
Loc: Cumberland, R I , USA42N71.4W
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Quote:
Another is that my eye's pupil is bigger than I think.
This is the most probable.
Actually, I just measured mine at approx 3.5mm, less than 2 feet from 130 watts of light.
I've previously had someone else measure my pupils when outside in full daylight. I get about 4mm-4.5mm.
I'd need to be looking straight up at a bright sunlit sky to get pupils down to 2-3mm.
edz
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Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
member#21
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GlennLeDrew
Pooh-Bah
Reged: 06/18/08
Posts: 1269
Loc: Ottawa, Ontario, Canada
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I'm sure the designers of lower cost instruments are well aware that rapidly/vigorously polished objective lens elements can suffer from turned edge. Lord knows, I've seen it often enough! Even a narrow zone of TE just a couple of millimeters wide in a 50-60mm objective is quite enough to introduce awful spherical aberration. (To appreciate why this is so, consider that an edge zone a mere 1.5mm wide on a 50mm lens contains nearly 12% of the lens area.)
An internal stop is a very good way to mask off the afflicted edge and hence deliver all that the objective is capable of. Indeed, even if an all-spherical objective was made perfectly, masking it down will still improve sharpness.
As Tony points out, for off-axis parts of the view different portions of the objective contribute to image formation. In his (nominally) 12X60, on axis the 52mm entrant pupil is exactly centered in the objective. For image points successively farther off axis, the 52mm entrant pupil moves off-center. In most cases, at the very edge of the field the entrant pupil extends *well past* the objective's edge, and hence includes some portion of turned edge. But other aberrations, de-focus, etc., will be vastly more injurious to image quality. Even for not-so-far-off-axis points in the image, the less-displaced entrant pupil will include some smaller portion of the objective's edge. But still, any extra SA introduced will almost certainly be insignificant.
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Home-made 11X50 right angle bino, 8.1 deg. FOV
Modified 26X100 bino, 3.5 deg. FOV
Home-made Mk II RA bino, using interchangeable objectives and eyepieces
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Mediocre minds discuss people. Good minds discuss events. Great minds discuss ideas.
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