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A system is focal if an object ray parallel to the axis is conjugate to an image ray that intersects the optical axis. The intersection of the image ray with the optical axis is the focal point F ′ in image space. Focal systems also have an axial object point F such that any ray through F is conjugate to an image ray parallel to the optical axis.
A principal focus or focal point is a special focus: For a lens , or a spherical or parabolic mirror , it is a point onto which collimated light parallel to the axis is focused. Since light can pass through a lens in either direction, a lens has two focal points – one on each side.
The Ilford Manual of Photography is a comprehensive manual of photography, originally authored by C.H. Bothamley and first published in 1890 by The Britannia Works Company, which became Ilford, Limited in 1901. The 1890 edition was revised by Bothamley many times over a period of forty years until the first multi-authored edition, edited by ...
The right figure shows how the image of an object point can be found by using three rays; the first ray parallelly incident on the lens and refracted toward the second focal point of it, the second ray crossing the optical center of the lens (so its direction does not change), and the third ray toward the first focal point and refracted to the ...
Thomas Sutton and George Dawson define focal range for what we now call hyperfocal distance: [2] Focal Range. In every lens there is, corresponding to a given apertal ratio (that is, the ratio of the diameter of the stop to the focal length), a certain distance of a near object from it, between which and infinity all objects are in equally good ...
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 ...
The 1996 third edition was re-titled as The New Fowler's Modern English Usage, and revised in 2004, was mostly rewritten by Robert W. Burchfield, as a usage dictionary that incorporated corpus linguistics data; [1] and the 2015 fourth edition, revised and re-titled Fowler's Dictionary of Modern English Usage, was edited by Jeremy Butterfield ...
In differential geometry, conjugate points or focal points [1] [2] are, roughly, points that can almost be joined by a 1-parameter family of geodesics. For example, on a sphere, the north-pole and south-pole are connected by any meridian. Another viewpoint is that conjugate points tell when the geodesics fail to be length-minimizing.