Author: Mark Mazour
One of the handiest things to have in the outdoors is a quality pair of binoculars. Whether you are hiking, viewing wildlife, hunting, or even at a sporting event, binoculars can bring the outdoors a little closer to you.
The second number, 42 in this example, is the diameter of the objective lens in millimeters. So a 42 designation means that the outer lens is 42 mm in diameter. A larger number indicates a larger lens. Large lenses are more bulky, but they also let in more light, making your image clearer - especially in low light conditions.
Your choice of FOV depends on your individual use of the binoculars. If you are using them in a wide-open area to scan for mule deer, a narrower field of view is not a big deal. However, if you are scanning a dense forest for hidden black-tailed deer at ranges at or around 100 yards, you will want to select a model that has a wider field of view.
In daylight, having a binocular with a larger exit pupil will have little effect. The only difference you may notice is that you will be able to move a binocular with a larger exit pupil and still maintain the image, which is extremely helpful if you are in unstable conditions, such as in a boat. The main difference occurs in low light conditions. If you plan on using your binoculars near dawn or dusk, which is a time when many hunters depend on their optics, it is recommended that you select an exit pupil greater than 4mm, to fully take advantage of the amount of light your eyes can let in. An exit pupil larger than your pupil’s diameter at the time does not result in a brighter image. Your eye can only handle so much.
You can see from the exit pupil calculation that if you choose a higher power binocular, you will also need to increase the size of the objective to maintain the same diameter of light leaving the binocular.