If you're like me, you probably have several years of ownership by different sets of binoculars - some good, some bad and some that were great. As birders, we need binoculars that are light, feel good in our hands, our attention quickly and work well in low light conditions. Rain, rain, dust, salt spray should consist of sealed after use. And if you as I age - there is nothing wrong with my eyes alone is never enough light at all - make sure you bring youra binocular that passes, a high percentage of light through the eyes. Finally, if you wear glasses, because I have to work with the binocular glasses. Many binoculars work if you take some care in your decision on the most expensive in economic terms, that will fill your needs. As in all things, it is always best, the best quality that can afford to buy.
DESIGN
All binoculars work basically the same. The light will be expandedflipped over, and exits to your eyes. They all focus by moving a lens or lenses. There are two major differences in design regarding the flipping. Flipping is necessary because the image would be upside down when viewing. Both designs use prisms set at certain angles. The angles reflect light off the prisms until the image is upright and is then passed on to your eyes. The placement of these prisms determines the binocular shape.
A guy named Porro first used prisms in the mid 1800s to both flip the image and provide a shorter light path, allowing shorter telescopes. Zeiss then used this system to develop hunting glasses and the binocular was born. The design remained unchanged until the mid 1900s. At that time the roof prism design was developed, allowing what appeared to be straight barrels for the light path.
The roof prism design was more complex and had more light loss through the reflections. Available light is decreased about 5% per reflected surface in uncoated lenses. Thanks to today's optic coatings this loss has been greatly diminished, thus allowing the roof prism design to become popular. The complexity of the prisms usually costs more to produce in the roof prism design - thus its higher price. Either design works well.
POWER AND LIGHT
Binoculars come with two numbers - 8X42 or 10X50 and so on. These indicate the magnification power and the diameter of the objective lens which lets light enter. Usually, the larger the magnification the better - right? Not always, and for different reasons. First, how much magnification can you hold steady before hand shake takes over. Again, as I've gotten older this affects me greatly with binoculars and cameras. It does little good to find that elusive bird only to see it trembling in the eyepiece. For myself and most others a 10X power is about all we can handle. I recommend a tri-pod when using powers higher than 10X. Second, the high power does little good if you are fixing on smaller quickly darting birds and you keep losing them in the narrow field of view.
The objective lens is the opening that determines how much light gets in. The higher the number - the more light and greater resolution. It doesn't end there, couldn't be that simple. The objective lens allows light IN. Lens coatings and the exit pupil will determine how much light gets through to your eye. Coating the lens with magnesium fluoride allows more light to get through. Multiple coatings allow even more. FMC - fully multi coated lenses means all air to surface lenses have been multi-coated to allow the maximum amount of light through. As always, the more coatings and better laying precision of those coatings results in more expensive binoculars.
OK, size of the lens allowing light in and lens coatings affect light in the binocular, but we still have to get light out. Light exits through the exit pupil. This is measured as the size of the circle of light exiting the binoculars. It is determined by dividing the objective by the power. So a 10x50 has a 5 mm exit pupil, a 10x32 has a 3.2 and so on. So what you may ask. Ok, the human eye pupil varies from @ 2 to 4 mm in daylight and as wide as 7mm or so in the dark. In bright daylight, you will gain no use in the larger objective lens. Your eye will not see the light or image in excess of its own pupil size. In bright daylight, using a smaller exit pupil could even outperform the larger. In low light, this changes completely. Your eye will need as much light as possible and will take in all available light exiting the binocular.
Confused yet? If not, just hang on. Now throw in the variable that as we age, our pupils open less, even in the darkest conditions. So as we age, even a higher objective lens may not help as our eye pupil opening will not allow in the light being supplied. Wow!That sums me up! For most birders a 5 or 6 exit pupil works pretty well in low light.
EYE RELIEF
We're not talking soothing eye drops here. You won't need them if your binoculars are right. Eye relief is the distance from the lens your eye will still be able to see the entire image. If you wear eyeglasses, this is a really important number. Your glasses will increase this distance and you will see only a center portion of what is available, so you are missing part of the fun, the scene and maybe even the bird. Plus if you are searching, you aren't seeing the entire image. What to do? Look for binoculars with "Long eye relief". This indicates the binoculars are designed with an eye relief of 14 mm or more. Standard eye relief ranges from 9 to 13 mm. Throw in the extra distance from your glasses and you lose a portion of the image. Many binoculars have foldable eye cups to help you get closer, but it is usually better to find longer eye relief and lay claim to your own set of binoculars.
WHAT TO AVOID
Avoid fixed focus binoculars, they won't function at close distances. Separately focusing eyepieces should also be avoided. They are clumsy and not quick enough for birding. Zoom binoculars are popular and have there place, but usually do not work as well as regular binoculars.
TIME TO BUY
Now, its up to you. Find the binocular that will fit what your plans and needs are. Make sure they are comfortable, light, and of the best quality you can afford. Good binoculars that fit you and your activities become unnoticeable after a while. Bad ones will leave your eyes tired and strained.You should be able to use binoculars for long periods without eye strain or discomfort. Make your decision based on your needs and hit the trails. Happy Birding!
More birding information, stories, and more at Fancy Flyers [http://www.fancyflyers.com]
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