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Binoculars for use in low light?

Discussion in 'Sights, Optics and Lasers' started by Syclone538, Jul 21, 2011.

  1. Syclone538


    Jan 8, 2006
    I know the brightness has to do with the magnifying power and objective lens diameter but don't know to what extent. 7x50 seem to be somewhat common and if I understand it correctly, should be brighter then either 7x35 or 10x50. Am I on the right track?
  2. eracer

    eracer Where's my EBT?

    Apr 5, 2011
    Tampa, FL
    Divide objective size by magnification to get a relative light gathering index, also called 'brightness index.'

    10x50 have an index of 5
    7x50 have an index of 7.14

    So all else being equal, the 7x50 binocular will be 'brighter' at a given illumination.

    But, since all things are not equal...

    The quality of the lenses, and the type of lens system. A 10x50 Swarovski binocular will be brighter than a 7x50 bargain brand (even though the 7x50 has a better 'brightness index,' simply because Swarovski glass is so much better - and so much more expensive.

    There are roof prism binoculars, with compact, straight barrels, and porro prism binoculars, with 'zig zag' barrels. In general, the better low-priced ones are porro prism, since it is more difficult to make a high-quality roof prism binocular. Roof prisms are nice, because they make for a lightweight binocular, but you have to spend a bit of money to get a quality roof prism set.

    With binoculars, you really do get what you pay for. I personally like a good quality 8x42 roof prism binocular for general purpose use.

    This Vortex Viper HD is a solid mid-price choice ($580). Compact and lightweight, with great optical performance.

    For a bit more magnification, and bit more brightness, look at the 10x50 porro prism offering from Steiner. Not as compact as the Vortex, but a very nice binocular around the same price ($550)

    I know that seems expensive, but an 8x42 Swarovski binocular will set you back about $2,000

    If you want a cheaper binocular, look at Nikon, Pentax, Leupold, and Brunton (which is a sneaky good optics company.) Also, Vortex makes some cheaper sets. You can probably tell I'm a Vortex fan...
    Last edited: Jul 21, 2011

  3. ratf51


    Aug 6, 2010
    NW GA
    Dividing the size of the objective lens by the magnification gets you the size of the exit pupil. A 10x50 pair of binocs will have a 5mm exit pupil. The larger the exit pupil the more light transmission. But, as eracer has pointed out, the quality of the glass also comes into play. The big question is this: how good are your eyes? The older we get the less our own pupils will dilate to let in light. It is possible to get binocs that will transfer more light than you can actually handle, thus you would not be able to discern a difference between a pair that optimizes your own sight capabilities and a better, more efficient pair that go beyond what you can take in light-wise.

    I cannot recall the size to which a human eye can dilate on average, but for some reason the size of 5mm comes to mind. And that may be for someone who has a few years under their belt, like those of us above the half century mark. If you are looking for binoculars it is best to find some place that carries enough of a selection so you can compare levels of quality along with varieties of magnification/objective.

    Another consideration is whether or not you wear glasses. You'll need to look for binoculars that are designed to be more easily used by someone with spectacles. Hope you find what you're looking for.
  4. Big Bird

    Big Bird NRA Life Member

    Aug 7, 2003
    Louisville KY
    Quality lenses are important but quality coatings matter as much if not more.

    Optics is one of the few areas where you really do pay for what you get. But lately I've found the European glass to have priced themselves out of all but the wealthiest clients.

    I have a pair of Swarovski SL binos and they were worth every penny of $800 I paid. But now the same binos are like $1500...and that's a lotta dough!
  5. eracer

    eracer Where's my EBT?

    Apr 5, 2011
    Tampa, FL
    That is certainly true.
  6. RayB

    RayB Retired Member

    Dec 2, 2005

    1) All true!

    Here's an easy optical formulary, with / representing division:

    Telescope Focal Length/Eyepiece Focal Length = Magnification

    Telescope Focal Length/Telescope Aperture = Focal Ratiio

    Primary Aperture/Eyepiece Magnification = Exit Pupil

    2) The answer is about 7 mm in younger people, and about 5 mm in adults. Anything above 7 mm is wasted on human eyes, and anything above 5 mm is wasted on most adult eyes. :fred:

    3) Sadly, there is no equation to calculate Eye Relief, as this is a function of eyepiece design; but long Eye Relief is a must for eyeglass wearers! :freak:

    Upping the magnification actually decreases the image brightness.

    10 X magnification is at the upper limit of hand holdability.

    Fast Focal Ratios = wider fields of view and brighter images.

    It's true that extras like optical coatings, blackened lens edges, internal light baffling, etc., make a huge difference in image quality. :wow:

    And while it's generally true that great optics are spendy, it's also true that you can get more bang-for-your-buck now than ever before, in many categories of optics!

    Orion is a good source for a wide variety of optics at great prices, and their customer service is excellent...

    Last edited: Jul 23, 2011
  7. wjv


    Jan 17, 2002
    Pacific NW
    Quality does count.
    Like everything else there are diminishing returns.

    You will get big gains going from something like a Big 5, made in China $20 specials, to a Nikon for $100-$125.

    You will still gain some going to a $500 pair, but not as much % wise.

    What to buy depends on what your intended purpose is.
  8. FLA45fan


    Aug 27, 2002
    I needed a small pair of waterproof, heavy duty use binocs. I found a pair of Steiner Navigator binocs 8x30's that perform pretty good in low light and have outstanding clarity. They are slightly larger than a pair of Leupold Wind River 10x23's that were my go everywhere binocs. They were at West Marine for $279 but price matched for 205. They seem to be identical (except for the darkk blue color) to the 8x30 Military/Marines that sell for considerably more. Compact, waterproof, great low light capabilities, armored, 2 bill$ - I couldn't ask for anything more.
    Last edited: Aug 22, 2011
  9. Wow, I didn't realize many others even concerned themselves with this stuff!

    Yes, exit pupil on a pair of binos is what's important. It matches the pupil opening on your eyes. So if you're young, your pupils can open up to 7mm to take advantage of a bino's exit pupil of 7mm. But as you get older, your pupils cannot open as wide, limiting it to 4.5 to 5mm or so (I'm talking 50+ y.o.), and even smaller with more age. At that point, any 7mm exit pupil would be a waste.

    And of course, light transmission through your binos is never 100%, so that's another factor that will reduce light entering into your eyes

    And polishing of the lenses is important. Cheaper binos only polish the lenses at the center area. Best binos polish the lenses all the way to the edges. As you can imagine, lenses polished to the edges gives clear images in the entire field of vision.

    The best test for any bino is, use it extensively, and if your eyes hurt, or if you get a headache, they're not good.

    As many have already said, with binos you get what you pay for, but I do think todays top-of-the-line binos are way overpriced. The glass technology hasn't improved much since at least the 1990s, but the coating technology have. But are they worth the tremendous increase in price? I don't think so.
    Last edited: Aug 18, 2011
  10. I bought all my binos in the mid 1990s. Can't see purchasing another pair today. No need to, and the prices are too damn high anyway.

    Zeiss 10x42 Classic (I love that design! I'm a Panzer commander!) for $700.

    Swaro 7 x 42 porro for $600.

    Steiner Military (to NATO specs) for $200 (after trading in a pair of Steiner Safaris).

    I also have a pair of Nikon "Superior E" 6 x 30 poro, for all around use. Great optics. So-so body fit and workmanship.

    But I digress.
    Last edited: Aug 18, 2011
  11. The 7 x 50 may prolong your use by 10 to 15 minutes.

    A smaller magnification (7x vs 10x) will give you a wider field of view. More useful if you're using the binos in wooded areas.

    And of course, 50mm binos are heavier than 30mm or 40mm ones because most of the weight is the glass. (Do not get those with cheap plastic lenses).
  12. RayB

    RayB Retired Member

    Dec 2, 2005
    Yeah, upping the magnification actually dims the image. That's why bigger objectives give better images at higher magnifications.

    Binoculars are really two small refracting telescopes mounted together to provide stereoscopic viewing in a handy-sized instrument. So, all the terminology and considerations that applies to telescopes, applies to binoculars.

    As I mentioned earlier, magnification is a mathematical value, and a constant:

    Telescope Focal Length/Eyepiece Focal Length = Magnification

    You know those cheap telescopes you'll sometimes see in department stores, that claim their 60 MM (two inch) $99.99 Refracting Telescope yields Up To 300 Power? Well, that may be true as far as the math goes...

    900 mm/6 mm = 150 X 2 (Barlow Lens) = 300 X

    ...but the images at that magnification will be useless!

    In that context, almost any scope can be almost any power!

    The useful maximum magnification of a quality instrument is along the lines of 50X per inch of aperture, or in the case of a 60 mm Refractor, up to 100X magnification. Some outstanding optics under ideal conditions can push this to 60X per inch, or so.

    But upping the magnification magnifies everything!

    The reason 50 mm field binoculars are limited to 10X magnification, is that 10X is at the upper limit of hand holdable.

    I can steady my 10 X 50's for only a few seconds at a time, while our 8X binoculars are much more forgiving! Guess which ones we use most?

    Last edited: Aug 24, 2011
  13. bustedknee

    bustedknee Curmudgeon

    Aug 1, 2001
    Wythe County, VA
    It is my opinion, the only way to get truly good binoculars that work for you and your unique eyeballs is, after taking into consideration all that has been suggested, try them under your conditions!

    Many years ago when I was much younger, and lived in Alaska, one of my buddies was in the market for new hunting glass. Since there were precious few places to shop and those were severely limited in selection and grossly over-priced for what they had on hand we did most of our shopping from catalogs.

    My friend researched what he thought he wanted then ordered a pair of binocs from each of the catalogs. Six boxes arrived the following week. He took all the binoculars outside a little while before dark and tested them.

    He returned 5 of the 6 binoculars for a refund on his credit card and kept the best.

    Now, why didn't I think of that? :notworthy:
    Last edited: Sep 4, 2011