Binoculars, Monoculars, Spotting scopes and on and on…. Why do we need them? These optical marvels have two basic functions: 1) To bring the objects closer to you; 2) To enlarge the object you are looking at. Now you may ask: "What is the best?" There is no simple answer to this question. We can say that the best optical equipment depends on your needs and possible area of usage. Here we will try to explain some definitions so that you can make an informed decision. Binoculars are intended for using both eyes with separate optical paths for each eye. Monoculars and Spotting Scopes are intended for using just one eye with single optical path. Weapon Scopes are the same as Spotting Scopes, but they have special weapon fixation with windage and elevation adjustments necessary for precise shooting. thus, such devices are specially designed to withstand recoil. Power Also known as Magnification, it is represented by an X sign in optics specifications. Power means the number that indicates how many times larger and closer you can see the viewed image. If you see binoculars marked as 7x35, or 5x25 this means that the first makes objects 7 times larger and closer, and the second - 5 times. Higher power does not always mean better. Objective lens size The objective lens is the lens collecting the light. It is the last lens on the optical path, being counted from your eyes. The objective lens size is the diameter of this lens in millimeters. This value is the second number in the examples above. The general rule with objective lenses is: higher diameter = increased light and increased brightness, with more detail and sharpness. This is a benefit for low light conditions. However, at the same time the weight and dimensions of a device with big lenses will be significantly larger than of one with smaller lenses. An objective lens over 50mm would be considered a luxury! Eyepieces also called oculars, are the lenses closest to your eyes Field of View is the size of an area seen. It is measured in degrees. The larger the field of view the more you can observe through your device. Apparent Field of View is the same measured in yards or meters. This is the maximum length of an imaginary pole that you can see from beginning to the end if this pole is located perpendicularly to the optical axis at some known distance (for example, it can be given as 154 meter @1000 meters) Exit Pupil is a diameter of the light beam exiting from the eyepiece. Larger exit pupils are useful when in darkness. Exit pupil should be a little larger than your pupil, but a huge exit pupil is useless because your eye cannot collect all of the light. Wide exit pupil increases the device weight and dimensions. Eye Relief is the distance the binoculars can be held from the eyes for comfortable observation. This distance is important if you wear glasses, or if you aim through a weapon scope. Near Focus Also called close focus, this is the closest distance from the binoculars where an object can be seen clearly. A very close near focus will compromise optical sharpness at distances. Brightness is the ability of a device to gather and transmit light sufficiently for good definition and color clarity. Resolution Also known as resolving power, this is the sharpness of the image. Sometimes it is discussed as overall resolution, meaning the entire view, or as resolution in the middle or at the edge, meaning the sharpness of the image in these areas of the view. Interpupillary Distance is the distance between the eyes, mentioned normally in reference to whether or not you can move the unit to compensate for different personal distances between the eyes. Dioptric Correction Based on the fact that 0 represents perfect eyesight, dioptric correction displays how you can adjust the focus on a particular device. It is usually displayed as ± 5 or as +6/- 4.