So, simply, there is no light on the outer edges of your pupil and thus the dark areas. The reason for this is that the exit pupil is smaller than your own pupil when viewing through the binoculars.
Larger exit pupils are preferred as the ease of viewing is improved less “dark circled edges” are visible in low light conditions and even eliminated during good light conditions. In the dim light, the pupil can widen up to7mm in this regard, the best. Ideal astronomy binoculars would be one with a higher exit pupil number. Therefore, 5.45 will be the binoculars’ exit pupil number. These numbers, taken individually or together, can tell you a lot about the. The number is calculated by dividing the second magnification number by the first, for instance in 8 x 42, (42 divided by 8 5.45). The exit pupil size indicates the size (in diameter) of the light beam exiting the binoculars at the eyepiece. The second number indicates the objective lens diameter for the binoculars. It should, however, be noted that there are other factors that influence the light-gathering capabilities of the binoculars such as the refractive index of the glass and coatings used to reduce this figure but can be ignored for now.Ī larger front diameter will also give you a larger exit pupil (if magnification is kept constant).
The reason for this is that an increase in the front element’s diameter will increase the light-gathering capabilities of the binoculars. Theoretically the larger the front element of the binoculars, the better the image result will be. Why is the diameter of the front element of any importance?