binoculars: please explain the 2 numbers

So I'm researching/shopping for binoculars for an upcoming Alaska cruise and am wondering if someone can explain the 2 different numbers in layman terms...

From what I have can figure out, the first number is magnification factor and the second number is the lens size... but what exactly does this mean when you compare models???

You are correct about the meaning.

The significance of the second number impacts the light-gathering capability. A 8x20 will give you 8x magnification the same as the 8x40, but the 8x40 will offer a brighter image at dusk or dawn when light is low.

The trade-off is up to you. If you expect to do most of your viewing in the daytime and want to travel light, the compact units with smaller objective lenses are fine. I you are spotting jaguars in a South American rain forest or whales on a cloudy Alaskan afternoon, light gathering may be more important.

Keep in mind that high magnification is great, but holding the binoculars steady is harder.

Dave

I usually try and get binoculars with greatest magnification with biggest lenses that is still small & compact . We have two 10x 20 that are physically smaller than my camera.

A larger first number, higher magnification, does exactly what it sounds like. Make things bigger. Unfortunately it has the bad side affect of also magnifying any movement of the binoculars. The higher the magnification the harder it is to hold steady enough so the image is not jumping around. I consider 10x to be about the maximum for hand holding. Even then I like to brace or rest the binoculars on something to help steady them. This is why they make stabilized binoculars. Expensive but it can really help.

Another thing to consider is the exit pupil size. This is the size of image coming out of the eyepiece and you divide the lens size by the magnification. So 10x50 binoculars have a 5mm exit pupil. That 5mm circle is where the image is. Generally a bigger exit pupil is better and is not so finicky to hold the binoculars in the right spot.

Another important spec is the eye relief. You'll probably have to look at the detailed specs for the binoculars you are considering. Binoculars with the same size lens and magnification can have different amounts of eye relief. More is generally better especially if you wear glasses. If you wear glasses and there is not enough eye relief you will notice that the image does not completely fill your eye so you just see a circle of an image.

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My 10x20 pocket binoculars are small, light and compact so they can be carried anywhere. Unfortunately their light weight does not dampen out any slight hand shaking made worse by the high magnification so the image really jumps around. The really small exit pupil size means I have to hold them in exactly the right spot to be able to see. Contrast them with my 8x42 binoculars which are bigger, heavier and have a slightly lower magnification. The weight dampens out minor vibrations and their big exit pupil means they can be quickly and easily brought up and see the image. The smaller magnification also give a broader view so objects are easier to spot with less panning around. They also have a much brighter image which is really noticeable in low light like under a jungle canopy or at night.

The little 10x20 are always in my travel kit even when I don't think I'll need binoculars. Anytime I know I'll be needing binoculars I take bigger ones like 10x42 or 7x32. The difference when using tiny binoculars versus full size ones is huge and if I have both the big and small ones at hand I'll always go for the bigger ones because I can see so much better. But when you're going on a shore excursion and don't know if you'll need binoculars the little ones get thrown in the bag just in case.

Thanks for the quick replies. I've tentatively narrowed my search to two Bushnell 8X42 models, both waterproof, under 2 lbs, 17 mm eye relief (I wear glasses) and under $200 (in Canada).

Now it is just a matter of finding them and "testing them" to see which feel better to me.

Thanks for the quick replies. I've tentatively narrowed my search to two Bushnell 8X42 models, both waterproof, under 2 lbs, 17 mm eye relief (I wear glasses) and under $200 (in Canada).

 

Now it is just a matter of finding them and "testing them" to see which feel better to me.

I just posted a link to the really complete Cornell Ornithology Lab report on binoculars. Check it out.

DON

Don... Just posted a link where?

I hope this is where you intended to link. The Cornell Ornithology website has a lot of great information about binoculars and I consulted it often when I was shopping.

Unfortunately quality glass is not cheap but modern manufacturing has improved the quality of even lower end glass. I think the key is to at least get off the bottom. Getting away from the $50 group and up into the $150+ category gets you a lot of bang for the buck and a noticeable improvement in quality. The $500 category is even better but gains in performance become more expensive until you are paying $2k for the last percent of performance.

Don... Just posted a link where?

 

I hope this is where you intended to link. The Cornell Ornithology website has a lot of great information about binoculars and I consulted it often when I was shopping.

 

Unfortunately quality glass is not cheap but modern manufacturing has improved the quality of even lower end glass. I think the key is to at least get off the bottom. Getting away from the $50 group and up into the $150+ category gets you a lot of bang for the buck and a noticeable improvement in quality. The $500 category is even better but gains in performance become more expensive until you are paying $2k for the last percent of performance.

This site

http://www.allaboutbirds.org/Page.aspx?pid=2674&__hstc=132624273.f0297d4aa241932b8525973fc097d8b9.1386889932925.1386889932925.1386889932925.1&__hssc=132624273.3.1386889932925&__hsfp=1717617835

has their yearly ratings for binoculars between <$200 and up to $2000. Note that the ZenRays that everyone on CC seems to love are reviewed but not too highly and are not on any of the top 5 lists.

DON

Variable dioptre eyepieces would be helpful as they may be able to avoid the need to wear glasses when using the binoculars.

Paul S