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Eye strain is the basic reason for choosing binoculars over monocular, because our predator eyes are designed for stereoscopic vision and strain when used otherwise.
From there, everything follows...
For long range spotting,
the big monocular up to 60x scopes are a compromise between comfort and portability. They are uncomfortable but portable (I am not aware of portable 60x binoculars). However, in addition to producing eye strain, their high magnification (e.g. 60x) requires a massive objective (e.g. 85 mm) to still produce minimal light transmission (85 mm divided by 60x = 1.4 mm light beam, which is half the 3mm beam a fully contracted human pupil can use). When combining eye strain, low light transmission and extremely narrow field of view, the practical use of 60x optics is quite limited. Yes they are the only way to score a trophy 1 mile away, but you better have good light, a tripod, a very still animal, plenty of time to set up, etc. etc.
This is why folks who really spend a lot of time glassing while hunting, go to the extremes of carrying tripod-mountable
big binoculars 20x or 30x in addition to the binocs around their neck, because spending a long time behind a monocular, regardless of the glass quality, creates too much eye strain. In the 1980's I used for years, when mountain hunting in France, a Nickel 15-60x56 telescopic monocular scope, and it was all but useless at 60x because light transmission was simply not good enough (0.9 mm light beam at 60x) so I rarely used it over 30x. I replaced it with 20x80 Steiner binoculars. I never missed the additional magnification, and the light transmission of the 20x80 binocs (80 mm / 20x = 4 mm light beam) was mind blowing after using the Nickel at 30x (56mm / 30x = 1.8 mm light beam). I can use them all day long, but I cannot use very long my 20-60x85 Razor Ultra HD spotting scope. It is great at the 1,000 meter range, but I much prefer the 20x80 binoculars for hunting...
The
typical 8x or 10x hunting binoculars are a compromise of comfort, magnification, and portability. They have lower magnification that spotting scopes but are highly portable and comfortable to use all day and still provide good light transmission during daylight (40 mm / 10x = 4 mm and 30 mm / 8x = 3.75 mm light beams) and enough magnification for use up to 400 or 500 meters.
Aside from easily fitting in a shirt pocket,
small low magnification monoculars (e.g. Zeiss 8x20 or 10x20) seem to combine almost all the disadvantages possible. Because they are very light and used one handedly, the image they provide is quite unsteady. Because they have a small objective, the light transmission is limited (20 mm / 10x = 2 mm and 20 mm / 8x = 2.5 mm light beam). Because they are monocular they are uncomfortable to use for long and cause eye strain.
If truly you do not glass a lot while hunting (????) and want something you can literally slip in a shirt pocket
Kevin, I would recommend a pair of
8x20 mini binoculars like the 1980's Zeiss 8x20B. These are true binoculars, top quality glass, very small, but they are quite usable for a quick glance here of there. I bought a pair in the 1980's, which I thought could replace my Zeiss 10x40 BGA when I was taking along my Steiner 20x80 Chamois hunting, but I quickly discovered that this was not true... For a while I tucked them in a shirt pocket when I went upland bird hunting, and now ... it has been so long since I used them that I could not even find them for the photo line up. That tells you all you need to know about how useful they turned out to be for me in the long run... There are a few of them floating on ebay in the $200 range, which is certainly a bargain for quality they represent, but likely represent the true hunting value of mini binoculars...
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From left to right:
- 1970's Nickel telescopic15-60x56 spotting scope. Barely usable above 30x due to a "small" objective. Obsolete.
- Steiner 20x80 binoculars. Enough magnification for spotting, still portable, all-day viewing comfort, but better used on a tripod.
- Zeiss 10x40 BGA: this was THE reference for all around binoculars for 20 years...
- Vortex Razor Ultra HD 20-60x85 spotting scope. Great at the 1000 meter range, but I still prefer the 20x80 Steiner for glassing/searching for hours while hunting...
- Leica Geovid 10x42 HD-D 3000. Would be the all around binocular perfection if just a bit more compact (compare with Zeiss 10x40 BGA).
- Swarovski 8x30 SLC. Perfect for stalking up close in dense bush or bow hunting.