Getting the Best Possible Image
Many shoppers looking for binoculars know next to nothing about them. They will look through a couple of pairs by different manufacturers and then pick the one that gives them the best image. This can and has resulted in a buyer thinking that an $80 pair of store brand binoculars is better than a $2500 pair of Swarovskis. This happens mainly because the shopper does not know how to properly focus the binoculars.
Everyone knows to look through binoculars and to turn the central focusing wheel to get the best image. However, not all know about the diopter setting that enables them to calibrate the binoculars. Calibration entails setting up the binoculars for optimal image clarity in both eyes, allowing for the fact that there can be differences between an individual’s right and left eyes.
To demonstrate that difference, look at the picture of the barn owl. The left side of the picture is in sharp focus while the right is fuzzy. It represents what the two eyes are seeing. The result of such a difference in visual acuity is often that the person will make the left side slightly fuzzy and make the right side slightly clearer, thus obtaining the clearest image possible without correcting for the difference between the eyes. This compromise is not necessary. It is entirely possible to get a sharp picture with both eyes. Let’s step through the calibration procedure.
The first thing to determine is whether you will be using the binoculars with or without glasses. If with, then the eyecups are down. If without, they are up. This positions the eyes at the correct distance from the back lens. You may want to go through the calibration procedure both ways, with and without glasses, to see what works best for you.
Next, if the binoculars have front lens covers, leave the right one closed and open the left one. Otherwise, put your hand in front of the right lens. Focus on an object in the store using the center focusing wheel (blue arrow). Remember the object you are looking at, because you will have to look at the same one again to focus the right eye.
Once you are happy with the left eye’s image, cover the left eye with the lens cover or your hand and then look at the same object through the right lens. You SHOULD NOT touch the center focus wheel. Instead you should focus the right lens using the knurled ring (green arrow in the right picture). Note, the knurled ring is difficult to turn. The stiffness is deliberate so it will not be accidently knocked off setting.
Now that both barrels are focused according to your eyesight, it is time to evaluate image quality. You will want to compare one set of binoculars with another. You MUST go through the entire setup process with both in order to get a fair comparison. Otherwise you will not be comparing apples with apples. You will be comparing apples with peaches, pears, or prune pits.
Asking the Sales Person “Which are ‘best’?” OR “Which ones would you buy?”
These questions can lead you into a mine field, so be careful. The word “best” is subjective and depends on the individual’s estimation of value. If the sales person expresses an opinion, it will be based on his values, not your’s. It is better to.figure out what’s “best” in your own mind based on your own values.
A good question to start off with is “What are the binoculars going to be used for?” If they will be thrown in a back pack and used to look at scenery in national parks, any decent quality binocular will do. The same goes for birding and sporting events. Decide what you like best within your price range. If the binoculars are going to be used for hunting, things get a bit more involved.
Where and what will you be hunting. If the game being pursued is to be pronghorns in Wyoming, you should lean toward higher magnification and lighter weight. Why? There is very little ground cover in pronghorn country so they are seen at great distances. 200 yards is a relatively short shot. Evaluating the quality of an animal’s headgear at such distances is easier with more magnification.
But doesn’t more magnification mean heavier binoculars? Not necessarily. All other things being equal, 10X32’s will be lighter than 10X42’s. The first number is the magnification and the second is the diameter of the front or objective lens. Weight is important in pronghorn hunting because you have to walk for miles every day and every extra ounce starts feeling like a brick.
If you are going to be stand hunting in the hill country or the brush country of Texas, the equation changes. 100 yards is a relatively long shot in those conditions. Raw magnification is not so important. What is more important is the amount of light the binoculars transmit since the critters tend to move in early morning and late evening when the light level is lowest. Under those conditions, the exit pupil becomes the primary consideration.
What is the Exit Pupil and Why is it important?
The exit pupil is the diameter of the front or objective lens divided by magnification. For example, in 10X42 binoculars the exit pupil is 4.2 millimeters. In 8X42s it is 5.25 millimeters or 25% larger. That can make a real difference when trying to see a black hog in the shadows at 6 a.m. Exit pupil can be hard to imagine, so let’s see what it looks like.
The white discs seen in the lenses are the exit pupil. The exit pupils on the left in the 10X42s are 25% smaller than those in the 8X42s on the right. The difference may be hard to see since it is so small. Let’s look at a more dramatic example.
This is a set of Nikon 10 to 22 power by 50 mm objective lens zoom binoculars. In the left picture the zoom is set to 10 power magnification, so the exit pupil is 5 mm (50/10) while on the right the exit pupil is only 2.27 mm with the power set at 22. The difference is obvious, but why is it important?
The Importance of the Exit Pupil
It might seem obvious that the darker the ambient light the more important it is to use as much of that light as possible to get the clearest image. However, the ability to use the light transmitted by the binoculars is very much dependent on the ENTRY PUPIL (or just pupil) of your eye. During the day, your eye’s pupil may be only 1 or 2 millimeters in diameter. In that case, just about any binoculars will transmit more light than your eyes can use. In the late evening or early morning, your pupil may be as large as 7 mm, or even 9 mm in people with extraordinary low-light vision. In those conditions, the eyes can use every bit of light the binoculars can transmit. That’s why lower magnification is often better in south Texas.
What About Coatings?
Optical coatings reduce internal light loss and glare and ensure even light transmission, resulting in greater image sharpness and contrast. Binoculars may have 10-18 glass surfaces, each one contributing to scattered light, so coatings make a big difference in what you see. Coated optics will have a less shiny, even dark appearance when looking into the barrel or tube; you may see a greenish, bluish, or brownish tint as well. Most coatings are magnesium fluoride or calcium fluoride and work by eliminating reflections. Therefore, more light enters your binoculars and is able to pass through to your eyes. Almost all modern consumer optics have some kind of coating on most of the optical elements. However, there are different levels and qualities of coatings.
“Coated optics” means that at least one of the major optical elements has a coating on at least one surface. “Fully-coated” means that all lenses and glass surfaces have a coating layer. “Multicoated” means that at least one of the major optical elements in a fully-coated binocular has multiple coatings of antireflective compounds on at least one surface. “Fully-multicoated” means all glass surfaces have multiple coatings and it is the best kind, resulting in light transmission of 90-95% for bright, sharp and contrasty images.
In extreme cases, 10X32 binoculars with superb coatings can transmit MORE LIGHT than 10X42s with inferior coatings.
What else should the customer look for?
The last really important variable is spherical aberration. It occurs when the light passing through the edge of a lens is not focused to the same point as that passing through the center. It is easier to understand looking at an example than a definition.
Please note that this example was shot using a pair of reading glasses. None of the binoculars you will encounter in Bass Pro are anywhere near this bad. You can see the results of spherical aberration in the apparent curvature of the vertical beam. This becomes of practical importance if a you are going to be glassing for hours on end looking for sheep, moose, or elk. This kind of image distortion, found most in low cost binoculars, causes headaches.
Bottom Line – THERE IS NO FREE LUNCH
Overall quality in binoculars is determined by the quality of the glass used (some very low end binoculars are made with plastic lenses), the coatings, mechanical precision and ruggedness, and warranty. Bass Pro strives to give good value for the dollar and thus stocks no bad binoculars. However, some are better than others. Based on the determining factors listed above, Swarovski binoculars are arguably the best in the world, followed closely by Zeiss and Leica. If you are looking for “best value,” or “most bang for the buck,” you are most probably looking for glass in the middle price range. Vortex binoculars, among others, are good candidates. Their unlimited lifetime warranty is unbeatable and their optics are excellent for the price. Swarovskis cost about five times more than Vortex. Are they five times better? Some people think so. Pursuits are about one fifth the cost of Vortex. Are they poorly made? No, they are not. You are well advised to determine your price range and then pick the best binoculars you can within that price range. Image quality usually defines “best” in a buyer’s mind, though warranty also often contributes to a final decision.
Good luck and enjoy your new binoculars!