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...

In photography, the 35 mm equivalent focal length is a measure of the angle of view for a particular combination of a camera lens and film or image sensor...

the flange focal distance (FFD) (also known as the flange-to-film distance, flange focal depth, flange back distance (FBD), flange focal length (FFL), back...

In film and photography, a prime lens is a fixed focal length photographic lens (as opposed to a zoom lens), typically with a maximum aperture from f2...

In digital photography, the crop factor, format factor, or focal length multiplier of an image sensor format is the ratio of the dimensions of a camera's...

called the "circle of confusion". The depth of field can be determined by focal length, distance to subject (object to be imaged), the acceptable circle of...

{o} }} and image distance d i {\displaystyle d_{\mathrm {i} }} to the focal length f {\displaystyle f} : 1 d o + 1 d i = 1 f {\displaystyle {\frac {1}{d_{\mathrm...

corresponding focal point is just the focal length of the system. In the more general case, the distance to the foci is the focal length multiplied by...

to a camera, or it might be interchangeable with lenses of different focal lengths, apertures, and other properties. While in principle a simple convex...

telescope's focal length f {\displaystyle f} divided by the eyepiece focal length f e {\displaystyle f_{e}} (or diameter). The maximum is limited by the focal length...

distance from this point to the lens is the focal length, though it is negative with respect to the focal length of a converging lens. Convex-concave (meniscus)...

{\frac {180d}{\pi f}}} degrees. The effective focal length is nearly equal to the stated focal length of the lens (F), except in macro photography where...

the vertex and the focus, measured along the axis of symmetry, is the "focal length". The "latus rectum" is the chord of the parabola that is parallel to...

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 (prime lens). A true...

approximation in techniques such as ray transfer matrix analysis. The focal length, f, of a lens in air is given by the lensmaker's equation: 1 f = ( n...

In contrast, depth compression and expansion with shorter or longer focal lengths introduces noticeable, and sometimes disturbing, distortion. Photographic...

photography and cinematography, in which the physical length of the lens is shorter than the focal length.: 93  This is achieved by incorporating a special...

on the retina of the eye.) The amount of magnification depends on the focal length of the eyepiece. An eyepiece consists of several "lens elements" in a...

dividing the system's focal length by the diameter of the entrance pupil ("clear aperture"). The f-number is also known as the focal ratio, f-ratio, or f-stop...

the origin O in the negative direction of the X3 axis, where f is the focal length of the pinhole camera. A practical implementation of a pinhole camera...

A varifocal lens is a camera lens with variable focal length in which focus changes as focal length (and magnification) changes, as compared to a parfocal...

wide-angle lens is a lens covering a large angle of view. Conversely, its focal length is substantially smaller than that of a normal lens for a given film...

differs significantly from what the object would look like with a normal focal length, due to the relative scale of nearby and distant features. Perspective...

equal to the reciprocal of the focal length of the device: P = 1/f. High optical power corresponds to short focal length. The SI unit for optical power...

typical at long focal lengths. Transverse aberration occurs when different wavelengths are focused at different positions in the focal plane, because the...

camera shake is a particular problem at slow shutter speeds or with long focal length lenses (telephoto or zoom). With video cameras, camera shake causes visible...

This is a list of smartphones with a telephoto lens that offers a focal length (35mm equivalent) of at least 115mm or “5x optical zoom” with a 1/3.5″ or...

by their focal length: a converging lens has positive focal length, while a diverging lens has negative focal length. Smaller focal length indicates...

optical power rather than focal length is that the thin lens formula has the object distance, image distance, and focal length all as reciprocals. Additionally...

but magnify the objects. The focal length also influences the ease of taking clear pictures handheld, with longer lengths making it more challenging to...