(Last Updated On: February 3, 2021)
The light beam’s width exiting the ocular, generally measured in millimeters, is the exit pupil (mm). Under low-light conditions, the larger the exit pupil, the clearer the picture will be. By dividing the objective lens size by the magnification capacity, exit pupil size is determined. For example, you want to know the 8×42 binocular exit pupil. 42mm / 8 = 5.25mm respectively. After it is fully dark-adapted, our Sports Optics’ exit pupil should correspond to the amount of dilation of your eye’s pupil. This number will range from 5mm to 7mm (the maximum amount for the human eye). A large exit pupil is not required for daytime vision, but that does not mean that we should not use a binocular for daytime viewing if it has a large exit pupil.
A broad exit pupil is preferred for marine use, as it is more tolerant and allows more binocular movement while keeping the picture in view. A binocular with a 7mm exit pupil can provide the optimum amount of light to the eye for night viewing.
Eye relief is the distance in mm between your eye and the eyepiece of the binocular/ spotting scope that enables comfortable viewing of the entire field of view. It calculates the spacing from the last surface of an ocular’s eye lens to the plane behind the ocular, where all the exit pupil’s light rays enter a focus and the image is created. Your eye should be positioned here to see the eyepiece’s full field of view.
Eye relief should be at least 10mm; the best support would be offered by 15mm, and if you wear eyeglasses, you will need more.
Place your eye on it to take advantage of the eye relief just below the eyepiece. If you put your eye further forward, you may lose the field of view and might even shift your vision out of the light beam from the eyepiece. Getting too close will stop you from blinking and can lead to a black ring appearing across the field of view as well.
How Significant Is Eye Relief?
When you use your spotting scope, eye relief is very critical when wearing prescription glasses or sunglasses. Any time you look through the area, it isn’t very pleasant to continuously take off glasses. For this purpose, you should look for a product that provides eye relief for a long time. This relates to the distance from which, while still being able to see the full vision, your eye will be from the oculus. At least 14mm of eye relief is recommended, though 17mm would be sufficient.
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