(Your shopping cart is empty)
Search 


Reach us at:
 
 
512-618-8880
You are here: Home > Published Articles > Binocular Adjustments and Selection

Recently, I was visiting with a couple about to go on their 10th safari and the subject of optics came up.  Before long, we decided to compare three binoculars with only me knowing what was presented and their prices.  Two were 10x50’s and one was an 8x42.  They ranged in price from $600 to $1,000 and the only criteria for comparison was image quality and ease of use.  The fact that one was an 8 power was to be overlooked.

 

Not surprisingly, the lady chose the most expensive pair, citing image quality as superior, as they arguably ought to be being the most expensive.  Her husband, however, “had no use for that binocular” because of the eye cups.  Being an eyeglass wearer, he said his wife’s choice was difficult to use and see through for him.  His choice was the least expensive $600 unit (though still a fine binocular).  I could be happy using any one of the three for the rest of my hunting days.

 

Interestingly, the eye cups my friend disliked so much were the most “high tech” of the lot, and they work great for my naked eyes (I wear glasses in the office, but not hunting).

 

This brings up an often overlooked aspect of binocular selection – ergonomics, or fit.  This is one of the pitfalls of buying a binocular online or out of a catalog without ever actually putting them to your eyes first.  They may not fit you!  If you’ve ever bought hunting boots this way, you know the problems – the heels may be too tight or loose, they may not be wide enough, or just rub you the wrong way.  Thankfully, most optics (and boot) dealers will allow you to return the product within a reasonable time if you are not satisfied with your purchase, but this can get to be a hassle.

 

There are four adjustments to be made with most binoculars, two of which you do almost automatically.  These are:  1) eye cups, 2) interpupilary distance, 3) main focus, and 4) individual eye focus.  If you don’t adjust each of these, you’re not getting the most out of your glass.

 

1)     Eye Cups.  If you wear glasses, twist or roll the eye cups down (making the bino shorter) or put them out if you don’t wear glasses.  It can make a big difference!  Binos are designed for a certain amount of eye relief, just like riflescopes.  And just like scopes, if you’re too close or far from that set eye relief, you don’t get the full image.  By wearing glasses, you’re forced to hold the bino further from your face.  By lowering the eye cups you get back that distance, putting your eye in the “sweet spot”.

2)     Interpupilary Distance.  This is the distance between the centers of your pupils.  The reason binos have that hinge in the center is for this adjustment (one of those almost automatic adjustments mentioned above).  If you have unusually close or far set eyes, you could have trouble with this adjustment.  I’ve had people approach me at hunting shows and their first question is something like “do you have a glass with an interpupilary distance of 78 millimeters?”  This is outside of the range of most binos, and for these folks, it’s more critical than anything else.  Kind of like the guy that needs a EEEE boot.  He can live with a less than ideal sole or not enough insulation if he can just find something that actually fits.  Kids on the other hand tend to have trouble with the minimum distance.  Just like eye relief, if this isn’t set right, you don’t get the full view out of your glass.  Most of us just give them a little squeeze or pull apart a little and don’t even think about it.

 

3)     Main Focus.  This is the other almost automatic adjustment.  Just give the wheel a little spin and everything looks good.  There are a few binos out there that are “fixed focus”, meaning there is no adjustment – you just put them to your eyes and look through them.  These can be wonderfully easy to use, but you give up a crisp picture at short distances, usually under 35 yards or so.  Unfortunately, I haven’t seen a quality fixed focus bino on the market for several years.  I used to use one and loved it.

 

4)     Individual Eye Focus.  I’m amazed at the number of people that aren’t aware this even exists, let alone how to set it.  On most binos, there is a ring on the right tube, just below the eye cup, that will adjust the focus for the right tube only, thus allowing you to set them precisely for your eyes.  Let’s say you’re 20/20 in one eye and 20/60 in the other.  Just using the main focus, you’ll never get a perfect focus because of this difference.  This adjustment ring, or diopter, allows you to correct for the difference in your eyes.  Here’s how it’s done.  I call it Eye Gymnastics.  Close your right eye (or put the right lens cap on), and use the main focus wheel to get the sharpest image.  Now, without touching the main focus wheel again, open your right eye, close your left, and use the diopter on the right tube and get the sharpest image for the right eye.  With that done (and you have to use the same focus point in doing this), open both eyes and your binos are now set exactly for your eyes.  There is usually some sort of incremental markings around the diopter so you can quickly check or reset the diopter without going through the drill again.  Some diopters will lock in place, while the current rage in a few top of the line models is to build it into the main focus wheel and you access it by popping the wheel in or out.  Regardless of its place, it is well worth making the adjustment.

 

Another aspect of fit that is often overlooked is the size and/or weight of a binocular.  Sitting in a deer blind, this isn’t too critical, but seven miles into a stalk on a cape buffalo in 90 degree heat, and a return walk ahead of you, you may question whether you really need a thirty something ounce 10x50 binocular around your neck.

 

 “Oh, but I need those big objective lenses to gather light!”  Let’s think about that.  The pupils of your eyes normally open up only to around 5millimeters in diameter.  The light that exits the back of a bino comes out in a tube of light about the same size; this is called the “exit pupil”.  You can see this by holding your bino out at arm’s length and looking through them.  The size of the exit pupil is easily calculated by dividing the size of the objective lens by the magnification (i.e. a 10x50 bino is 50mm objective lens divided by 10 power= 5mm – just the maximum size of your pupil!).  Anything larger than this is theoretically wasted, and if it’s broad daylight, your pupils aren’t 5mm any more – more like 2mm.  So, back to that buffalo hunt (or sheep, goat, antelope, elephant, etc.), maybe you don’t need crack-of-dawn light gathering ability but dropping 10, 15 or 20 ounces around your neck might be a better option.  Visualize hanging a standard soda bottle around you neck – that’s what you’re saving!  To do this, think about an 8x25, 8x32 or 10x32 bino.  You’re still looking at about a 3mm exit pupil – plenty for daylight – and you’ve saved all that weight.  Heck, you could just put them in your pocket or belt pouch and have nothing around your neck.  Think about it for that next long hike.

 

A binocular harness is also a big help in this area, especially as binocular weight increases.  It gets the weight off your neck and spreads it out over you shoulders.

 

I’ve had folks at my booth at hunting shows trying to decide between two different bino makes and models and they can’t seem to see any difference in image quality.  “Ok, close your eyes and use them.”  I usually get a strange look from them at that point.  “Close your eyes and see how they feel.  Can you reach the focus wheel easily?  Do the eye cups fit your eye sockets comfortably?  Which one fits in your hands the best?”  “Well, yeah, these feel better than those.”  “If you can’t see a difference in image quality and these feel better, there’s your answer.”

 

“Yeah!”