Camera lenses have many features, several of which have numbers associated with them. The focal length is measured in millimeters, abbreviated "mm." The larger the number, the more powerful the zoom. There are several categories of lenses based on focal length.
Standard Zoom
Standard zoom lenses have focal lengths of between 40 and 60 mm. They are known as standard zoom lenses because they represent the approximate angle of view of the human eye.
Wide Angle Lenses
Wide angle lenses encompass a larger field of view than standard zoom lenses and have focal length between 20 and 40 mm. These lenses increase the depth of field. However, this lens will exaggerate the size of subjects close to the lens.
Ultrawide Angle Lenses
These are lenses with focal lengths of less than 20 mm. They have the widest viewing angle of any lens. However, with this wide view comes increased distortion through enlargement of close subjects and shrinkage of subjects farther away.
Catadioptric Lenses
These are lenses that have a focal length of 800 mm or more. They are typically used for astro photography.
Telephoto Zoom
These lenses have a focal length of between 70 and several hundred mm. These lenses can zoom in on subjects far away but will make objects in the distance appear larger than they actually are.
Calculating Zoom
To calculate the zoom of a camera lens, divide the maximum focal length by the minimum focal length of the lens. For example, if a lens' focal range was from 20 to 100, it would have a zoom of 100 divided by 20, which is 5.
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