How do I know which size objective lenses will work best for me? Most compact and mid-size binoculars have objective lenses in the 25mm to 36mm size range. Full size binoculars have objective lens sizes ranging from 40mm to 56mm on average. The size of your objective lens will determine many factors in the performance of your binoculars. The smaller the objective lens the lower your field of view will be. This might not be important if all you need to see is several yards through thick brush or trees. In open areas, smaller fields of view can be the difference between seeing a few animals in a herd, and the whole herd. The size of your objective lens also has a direct impact on the light gathering capabilities of your binoculars as well.

What does light gathering capability mean to me? Remember the smaller the objective lens the less light that can pass through the lens to your eye. Magnification also plays a crucial role in light gathering capabilities. Binoculars with lower magnification have larger fields of view, which means more light can be passed to your pupils. The key when determining how well your binoculars will perform in low light situations is called the "exit pupil". This term is shown in millimeters and refers to the width of available light coming out the viewing end of your binoculars. The pupil in the human eye can only gather so much light in situations where available light is scarce. A pair of binoculars with an exit pupil of 5mm or greater will perform the best in low light situations. How does this relate to the size of your objective lens and magnification? The smaller the objective lens the less available light that can pass through your objective lenses. The greater the magnification, the less available light that can pass through to your pupils. Keep this in mind if light gathering ability is one of your main features in choosing a pair of binoculars.

The final piece of the puzzle is the quality of the lenses and prisms in your binoculars. The old saying "you get what you pay for" applies here to an extent. Most of the binoculars in the $200+ price range feature better lenses, lens coatings, and prisms. But what does all this mean? Let's start with the lenses first. Good quality lenses will be smooth and symmetrical in size through out. Even small flaws, waves, or discrepancies in lens density can mean poorer clarity and viewing performance. The best way to see this difference is to pick up a $25 pair of compact binoculars, and compare them to a larger $300 pair. You should immediately see a huge difference in brightness and clarity through the entire field of view. Some less expensive binoculars are very clear in the center of the viewing frame, but get blurry as you look towards the edges of the field of view. The coatings that manufacturers put on lenses also help clarity and light gathering capabilities. It's like looking through a quality pair of polarized sunglasses, versus a $5 pair at the gas station.

Company Resource: Big Porro Binoculars, Compact Porro Binoculars, Monocular Telescope