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Focal length. 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 positive focal length indicates that a ...
Diagram illustrating the flange focal length of an SLR–type and a mirrorless–type camera. For an interchangeable lens camera, 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 focus [1] or register, depending on the usage and source) of a lens mount system is the distance from the ...
f-number. Diagram of decreasing apertures, that is, increasing f-numbers, in one-stop increments; each aperture has half the light-gathering area of the previous one. An f-number is a measure of the light-gathering ability of an optical system such as a camera lens. It is calculated by dividing the system's focal length by the diameter of the ...
So a standard 50 mm lens for 35 mm photography acts like a 50 mm standard "film" lens even on a professional digital SLR, but would act closer to a 75 mm (1.5×50 mm Nikon) or 80 mm lens (1.6×50mm Canon) on many mid-market DSLRs, and the 40-degree angle of view of a standard 50 mm lens on a film camera is equivalent to a 28–35 mm lens on ...
On a crop camera with APS-C/H size sensors, it only yields a cropped circular and full-frame image. A zoom lock is included which avoids leaving the focal length range of full coverage on crop sensor cameras. Nikon AF-S Fisheye Nikkor 8–15 mm f /3.5–4.5 E ED – designed for full-frame and FX cameras, this lens behaves identically to the Canon.
Using a positive lens of focal length f, a virtual image results when S 1 < f, the lens thus being used as a magnifying glass (rather than if S 1 ≫ f as for a camera). Using a negative lens ( f < 0 ) with a real object ( S 1 > 0 ) can only produce a virtual image ( S 2 < 0 ), according to the above formula.
Normal lens: angle of view of the diagonal about 50° and a focal length approximately equal to the image diagonal. Wide-angle lens: angle of view wider than 60° and focal length shorter than normal. Long-focus lens: any lens with a focal length longer than the diagonal measure of the film or sensor. [10] Angle of view is narrower.
35 mm equivalent focal length. The resulting images from 50 mm and 70 mm lenses for different sensor sizes; 36x24 mm (red) and 24x18 mm (blue) 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 size. The term is popular because in the early ...