The largest groups of people among the populations who love making use of binoculars are bird watchers. While some people believe that binoculars are all the same, experienced bird watchers know that there are certain features that are a must if anyone is going to enjoy their bird watching experience to the core; a good birdwatching binoculars should include these features:
Close focus: This refers to the close distance that a binocular is able to focus; a good binocular is one with a strong close focus because even though in many cases birding occurs from a distance, there are times when a close of focus of 10 feet will be good enough but we have strong binoculars whose close focus is actually 3 feet.
Magnification of Lenses: Magnification is a strong feature in any binocular because it indicates how many times closer it will bring an object at a distance. If there is a number like 750 in the binoculars this indicates that its magnification is 7 and that means the image will appear to be 7 times nearer than it really is; if a bird was 70 feet away, the binocular will make it appear like it is only 10 feet away.
Exit pupil: This refers to a small circle in the eyepiece of the binoculars that contains the image. The pupil of your eye dilates in regards to the prevailing lighting conditions so that the size of the pupil matches the size of the exit pupil.
Eye relief: This refers to the distance between the eyepiece of the binoculars and the surface of your eye. The re should be sufficient distance between the eyepiece and your eye such that your eye doesn’t touch the surface. The reason for this is that it actually determines the field of view you are able to see. When the eye relief is long you don’t have to place the binocular very close to your eye such that the eyelashes get into your way. The purpose should be preventing your eyeglasses if you use them from coming too close to the eyepiece.
Twilight factor: Twilight factor refers to the amount of light brightness the binocular is able to focus on in conditions where the light is a little dim. Twilight factor is determined by multiplying magnification with the diameter of the objective lens after which you get the square root of the answer you got. The secret is getting a binocular whose twilight factor is large which means it will work much better in conditions where the light is dim. Birding binoculars with twilight factors of close to 20 normally work best.
Prism: Prism in binoculars refers to how light changes direction using the principal of internal reflection; binoculars use two basic types of prisms namely porro prisms or roof prism. In the porro prism the binoculars’ objective lens is normally set far away from the eye piece while in the roof prism the eye piece and the objective lens are set in a straight line.
Coatings: Optics in the binoculars is coated on both ends in order to enhance its light transmission abilities because loss of light from internal reflections normally brings out fuzzy images that have a low contrast.