Magnification: is simply the degree to which the object is enlarged. With a 7x35 binocular, for example, the object appears to be seven times closer than without the aid of a binocular. The number immediately following the "x" is the diameter in millimeters of the objective (front) lens. A 10x50 binocular, therefore, has a 10 times magnification with a 50mm objective lens.
Field of View (FOV): The field of view is the width, measured in degrees or feet, of the viewing area you would see at 1,000 yards.
Bright Source or Over-Light Protection: An electronic circuit that turns the power to the night vision device down or off when it is exposed to bright light (such as automobile headlights). This protects the image intensifier and extends its life. The device will revocer and resume normal operation in 1-2 minutes.
EyePiece Focus: Used to match your night vision scope or binocular to your specific eyesight.
Image Intensifier Or Intensifier Tube: The active component in a night vision system that amplifies light and presents a usable image.
Infrared (IR) Illuminator: Provides a light source for the system to amplify, yielding enhanced images in very low light conditions such as caves where no ambient light is available for amplification.
Objective Lens: Collects all available light and focuses it on the image intensifier. It also provides image magnification.
Phosphor Screen: Positioned at the back of the intensifier tube, the green phosphor screen renders a visible night vision image. The human eye is most sensitive to green contrasts.
Photocathode: Converts light (photon energy) into electrons (electrical energy) which are then amplified in the intensifier. The objective lens focuses available light on the photoelectric surface of the photocathode, which is excited and passes electrons within the tube.
Resolution: A measure of the ability to render and display a detailed image. Image intensifier resolution remains constant and is expressed as the maximum number of line pairs per millimeter (LP/MM) that can be discerned when a black-and-white stripe pattern is focused on the photocathode.
Exit Pupil: The exit pupil refers to the size of the shaft of light transmitted to the eye. The more light, the better the contrast. You can actually see the exit pupil by holding the eyepiece of the binocular approximately 12 inches from your eye. It is the bright circle of light in the center of the eyepiece. Exit pupil is expressed in millimeters and is normally derived by dividing the power into the objective lens diameter. A 7x35 binocular has an exit pupil of 5mm (35 Ã· 7).
Prism Systems: Binoculars have left and right side barrels linked to each other by an axle. The two most frequently used prism systems are porro and roof. Porro Prism binoculars are characterized by the eyepieces being offset from the objective lenses. Roof Prism binoculars feature lenses positioned in line for a more compact design.
Coated Optics: Optical glass surfaces are coated by magnesium fluoride to reduce light loss and glare due to reflection. Most binoculars are fully multi-coated to further enhance viewing and reduce eye strain. Some binoculars have a special image enhancing, amber, high contrast coatings.
WaterProof: This describes a binocular's ability to remain completely dry on the inside when exposed to moisture or total submersion in water. Binoculars are sealed with O-rings and are filled with 100% arid nitrogen, which also resists all forms of moisture.
Stray Light: When light entering the binoculars reflects off of interior surfaces, the reflected light eventually exits inside the binoculars in the form of stray light. This unfocused light typically diminishes the image quality of the sight picture.
Focusing Range: All binoculars have the ability to be focused for infinity. So a primary point of distinction between binocular models is the minimum focus range. Birders tend to favor models with a short focus range of about 15 feet, but 20 to 25 feet is usually acceptable.
Twilight Performance: Using the below formulas gives a basic evaluation of low light performance, however, one must keep in mind that they are mathematical formulas and do not take into effect some of the most critical features in optics: glass quality, number of lenses, precision of manufacturing and coatings.