Magnification is the degree to which the object being viewed is enlarged. Magnification is one of the very important reasons why most people buy a pair of binoculars. The common binocular magnifications are 6x, 7x, 8x, 9x, and 10x. The exact magnification that a binocular provides may be calculated from the focal length of the objective lens and eyepiece. However, in practice, the magnification relies almost exclusively on the diameter of the objective lens.
In a binocular designation (7 X 35, for example) the first number indicates the magnification, or how much larger, or closer, the object will appear than seen with normal vision. When considering magnification, more is not necessarily better. As magnification increases, brightness and clarity may diminish, depth of field can become shallower and the field of view is usually more restricted. More noticeable and disturbing at higher powers are fine hand tremors and the effects of atmospheric conditions, such as the distortion caused by heat waves.
For birding or an observation primarily at a close range the 6, 7 or 8 power binoculars are the best choice. This range of magnification generally offers you a precise and wider field of view with better image quality. For long distance viewing or where greater detail is required, a higher magnification of 8, 9 or 10 should be considered. Magnification, as a binocular parameter, should be considered as it relates to other factors such as aperture size, exit pupil, hand-held stability, atmospheric conditions, available light, optical design and the weight of the binocular. If the magnification increases, the eye relief, field of view, and brightness diminish, and images may shake. Â
