Search results
Results From The WOW.Com Content Network
The focal point F and focal length f of a positive (convex) lens, a negative (concave) lens, a concave mirror, and a convex mirror.. The focal length of an optical system is a measure of how strongly the system converges or diverges light; it is the inverse of the system's optical power.
A 100 mm focal length f /4 lens has an entrance pupil diameter of 25 mm. A 100 mm focal length f /2 lens has an entrance pupil diameter of 50 mm. Since the area is proportional to the square of the pupil diameter, [6] the amount of light admitted by the f /2 lens is four times that of the f /4 lens.
35 mm equivalent focal lengths are calculated by multiplying the actual focal length of the lens by the crop factor of the sensor. Typical crop factors are 1.26× – 1.29× for Canon (1.35× for Sigma "H") APS-H format, 1.5× for Nikon APS-C ("DX") format (also used by Sony, Pentax, Fuji, Samsung and others), 1.6× for Canon APS-C format, 2× for Micro Four Thirds format, 2.7× for 1-inch ...
Instead, the angular aperture of a lens (or an imaging mirror) is expressed by the f-number, written f /N, where N is the f-number given by the ratio of the focal length f to the diameter of the entrance pupil D: =. This ratio is related to the image-space numerical aperture when the lens is focused at infinity. [3]
Nikkor 28–200 mm zoom lens, extended to 200 mm at left and collapsed to 28 mm focal length at right. A zoom lens is a system of camera lens elements for which the focal length (and thus angle of view) can be varied, as opposed to a fixed-focal-length (FFL) lens ().
Following historical convention, the circle of confusion is sometimes taken as the lens focal length divided by 1000 (with the result in same units as the focal length); [2] [3] this formula makes most sense in the case of normal lens (as opposed to wide-angle or telephoto), where the focal length is a representation of the format size. This ...
The term telephoto ratio refers to the physical length of a lens divided by its focal length; where long-focus lenses have a telephoto ratio around 1, telephoto lenses have a ratio less than 1. As an example, one modern lens ( Canon EF 400 mm f /4 DO IS ) achieves a telephoto ratio of 0.58 in part due to a front (converging) lens group which ...
Notice that the shorter the focal length and the larger the angle of view, perspective distortion and size differences increase. Lenses are often referred to by terms that express their angle of view: Fisheye lenses, typical focal lengths are between 8 mm and 10 mm for circular images, and 15–16 mm for full-frame images. Up to 180° and beyond.