The first question I have to ask myself when choosing a new pair of binoculars is "what will I be using them for the most", and "what is most important to me". Let's start with the first part of the question. What will you be using your binoculars for the most? I do a lot of tree stand hunting during the season, and archery season is my favorite time of year. I also take trips up north when possible and use my binoculars to glass crop field edges and ridges. Knowing this, I can rule out large sized, large magnification, bulky models. I need a pair of binoculars I can wear around my neck while in the stand or while stalking, that won't get in the way, but also have the right magnification to use while sitting on large crop fields up north or pastures here in Florida. Weight, size, and light gathering capabilities are the most important factors to me in choosing a pair of binoculars. Let's discuss these factors in more detail.
Is weight the most important feature to you? Tree stand hunters don't want a heavy pair of binoculars that weigh them down in the tree, plus glassing is not as enjoyable with a heavy pair of optics. If you are going to use your binoculars from a vehicle or while glassing open terrain, weight might not be as big of an issue to you. Just a few ounces can be a big difference when using your binoculars for several minutes at a time.
How about the size of your binoculars? Many companies now offer their lines of binoculars in three categories, compact, mid-size, and full-size. When archery hunting a big pair of binoculars can get in the way during crucial moments while trying to get a shot. However, most compact series binoculars lack the light gathering capabilities that mid-size and full-size models have. Many turkey hunters like to use compact binoculars that can easily fit in a shirt pocket when not in use. Having a good set of compact binoculars can be a great asset when you don't need to see more than 100 yards or so. However in open areas or in low light situations, they can hinder your ability to judge an animal at a distance. Choosing the right size range is the next step in narrowing down which pair is right for you.
What objective power do I need? This is probably the most commonly asked question in determining which pair of binoculars to choose. Magnification averages from 7X to 16X for most manufactures, with larger magnification models available. I personally like the magnification of a 10X binocular. Some hunters who primarily hunt dense brush or thickets don't need that much magnification, while other hunters out west need magnifications greater than that while glassing distant ridges for big game. Most archery hunters don't need more than 7X or 8X binoculars, but if you are also a rifle hunter that extra little bit of power can be a tremendous help. Magnification is also dependent on the size of your objective lens for how well they will perform during those early mornings, late evenings, or cloudy days.
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.