binoculars

How to choose good binoculars

Binoculars are basic equipment for birdwatching, but many beginning birders don’t know how to choose good binoculars, or even what all the numbers and binocular feature terminology means in terms of quality optics. Here, then, is a binocular primer for beginning birdwatchers. Before you go out and decide that the binoculars with the biggest price tag must be the best, spend a little time educating yourself.


Binocular Magnification

Binoculars have a pair of numbers that everyone sees first. They might be listed as 8x30, 8x42 or 10x50, but what do these binocular numbers mean? The first number is the magnification. Binoculars with an 8x30 or 8x42 rating, for example, both magnify objects by exactly 8 times. In other words the object will appear 8 times bigger than normal. One of the most common mistakes people make when buying binoculars is simply buying the highest magnification you can find. This is especially true for binoculars that are meant for birdwatching. There are several problems with too much magnification. First, as those of you with digital cameras may already know, when you use high magnification, or high zoom with your camera, it is very difficult to hold the image steady. The slightest movement of your hand or the binoculars is magnified, resulting in an image that bounces all over the place and is hard to keep within the field of view. The second reason why too much magnification can be negative has to do with the overall clarity and brightness of the image, but that involves the second number as well.


The Second Number in a Binocular’s Rating

The second number is the size in millimeters of each of the binoculars’ outside lens. In the case of binoculars, size does matter and bigger is better. The size of the lens is the limiting factor in determining how much light enters the binoculars and ultimately makes its way through to your eyes. A bigger lens size means more light enters and your image appears brighter and sharper. So binoculars with a rating of 8x42 will give you a brighter and sharper image than binoculars that are rated 8x30 even though both are magnifying the image by a factor of eight. It’s easy when comparing binoculars of the same magnification, but is 8X42 better or worse than 12x50 for brightness? To compare binocular image quality between different magnifications, we need to do a little math. We simply divide the second number by the first. So 8x42 binoculars give us 42 divided by 8 or 5.25. This is called the exit pupil. The bigger the exit pupil, the brighter the image will be, all else being equal. With 12x50 binoculars, then we get an exit pupil of 50 divided by 12 or 4.167. SO the 8X42 binoculars would be brighter. For birding, I recommend an exit pupil around 4 or more. There are times when you’ll be under a dense canopy or birding at dawn or dusk when the light is limited so the extra brightness will make a big difference.


Binocular Lens Glass and Lens Coatings

Brightness and image clarity are also strongly affected by the quality of the lens glass and the coatings applied to the lens. Binocular lens glass should be Bak4 although some lower quality binoculars use BK7 glass which is much cheaper to produce. No matter what the salesman tells you, go with Bak4 glass for the lens and prism of your binoculars. Bak4 glass is a higher density and provides superior contrast, better brightness and a sharper image due to a reduced internal light scattering. If you are investing in a good pair of binoculars for birdwatching, don’t cheap out on the glass quality. Coatings reduce reflected light and increase the amount of light that passes through the binocular lens and to your eye. Remember lens coating is probably the biggest factor is the brightness of a pair of binoculars.


Types of coatings found in binoculars are:

Uncoated: Don’t buy uncoated binoculars. As much as half the light can be reflected away by an uncoated lens.
Fully coated: a low cost, relatively inefficient lens coating. Avoid fully coated lens binoculars even though they may be less expensive.

Multi-coated: multi-coated binoculars use several layers of coating to provide the highest amount of light pass through. Note, however, that multi-coated means that not all of the lenses within the binoculars are multi-coated.
Fully multi-coated (sometimes abbreviated FMC): this is the same as multi-coated, but every lens in the binoculars is treated with the multi-coat. If at all possible, buy fully multi-coated (FMC) binoculars for the best and brightest image.
Other Important Binocular Ratings

For birdwatching, minimum focus, also called minimum focal distance or close focus, is very important. If you are trying to see anything closer than the minimum focus with your binoculars, you will not be able to focus them properly. In birding, most of the birds will be relatively close, perhaps even closer than 10 yards as you look directly up into the branches of a tree. Choose a close focus that is relatively low for birdwatching.

Durability can be an issue for field work. If you are traipsing through the woods or over ledges, then you may want to consider armored binoculars. Armored just means that they have a resilient, rubberized coating to help reduce (but not prevent) damage if the binoculars are dropped or bumped. If you go birdwatching by boat or in the rain, then consider waterproof binoculars. If you get water vapor inside your binoculars, they’ll be useless until you are able to thoroughly dry them again (which will likely take days).

The size of your binoculars is an important consideration. Many a birder has purchased the best binoculars they could find only to find that they are too big and too heavy to comfortably carry for a full day of birding. A good pair of smaller field glasses will get more use if you make frequent birding trips. On the other hand if you are watching from a stationary location, like your deck, then the bigger binoculars will usually give you a better experience. Either way, make sure you are comfortable with the binoculars.

Most quality binoculars will have a threaded insert on the underside for use with a tripod. A tripod is used to steady the binoculars and is especially helpful if you are using binoculars with a higher magnification or are trying to pick out finer details to make a tricky bird identification.

The most important thing to remember when buying binoculars is to try them out. Make sure they fit your face, and that the weight and size is appropriate for your needs. If you are shopping in a store, then try a wide variety of shapes and sizes to see which is the most comfortable.


http://www.chatterbirds.com/shop.aspx
http://www.the-binoculars-store.co.uk
http://www.binocularreviews.org.uk/.