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Night Vision Terminology

by Staff Writer

Night vision scope

There's quite a bit of science that explains night vision, but only a few terms will be important as you choose a night vision device. When you're searching for optics and binoculars to use for night vision, you will want to pay attention to such things as light amplification, resolution and clarity. The following terms can help you understand what aspects of your night vision device will affect how well you see when you use it.

Night Vision Terms:

  1. Diopter: A diopter is a measurement referring to the optical power of the night vision lens. This measurement is also indicative of the way optics are focused and the focal length of your night vision binoculars or scopes.

  2. Exit pupil: This term refers to the measurement, in millimeters, of light that comes out through the eyepiece. Most night vision devices will have a large exit pupil, at least 7 mm in diameter, to let as much light into the user's eye as possible. The more light that reaches your eye through your night vision device, the easier it will be to see.

  3. Eye relief: A measurement in millimeters of the distance between the eyepiece and the eye; this is particularly important to eyeglass wearers who use night vision, as eyeglass wearers need a longer eye relief to see the full field of view. Similarly, hunters and others using night vision scopes need a longer eye relief on weapon-mounted night vision in case of kickback.

  4. Gain: The gain of a night vision device is the number of times a night vision device amplifies light. The more times light is amplified, the more detail you will be able to see through your night vision device.

  5. Line pairs: Line pairs are a measurement of image resolution; the more line pairs, the sharper the resolution of your night vision device will be. When you're using night vision, higher resolution means you will be able to see more detail and it will be easier to spot what you're looking for.

  6. Objective lens: Night vision devices have multiple lenses, and the objective lens is the lens (or lenses, if you're using night vision binoculars) closer to the object being looked at. The larger the objective lens is, the more light will be let in, making it easier to view objects in the dark.

  7. Photosensitivity: Photosensitivity is a measurement of the ability of a night vision device to amplify light. The more sensitive to light your night vision goggles or binoculars are, the more light will reach your eye.

  8. Tube blemishes: In night vision, tube blemishes are usually small spots common to all night vision devices. The more tube spots there are, or the larger they are, the harder it will be to see. A night vision device with small or few blemishes will be accompanied by a higher price.

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