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Phase-detection autofocus "sees" through window glasses without problems and is much more accurate, but it does not work in low-light conditions or on surfaces without contrasts or with repeating patterns. A very common example of combined usage is the phase-detection auto-focus system used in single-lens reflex cameras since the 1985s. The ...
By measuring this zone, the autorefractor can determine when a patient's eye properly focuses an image. The instrument changes its magnification until the image comes into focus. The process is repeated in at least three meridians of the eye and the autorefractor calculates the refraction of the eye, sphere, cylinder and axis.
Eye autofocus may refer to: . Face detection system used to focus on the subject's eyes; Eye-controlled focusing, where focusing is controlled by the photographer's eyes; Eye tracking is the process of measuring either the point of [[Gaze (physiology)|gaze] or the motion of an eye relative to the head
Time of flight of a light pulse reflecting off a target. A time-of-flight camera (ToF camera), also known as time-of-flight sensor (ToF sensor), is a range imaging camera system for measuring distances between the camera and the subject for each point of the image based on time-of-flight, the round trip time of an artificial light signal, as provided by a laser or an LED.
For example, in a backlit situation a rising sun may be behind a person whose face will be much darker than the bright halo around the body and hairline. Spot metering allows the camera to measure the light reflected from the person's face and expose properly for that, instead of adjusting exposure for the much brighter light around the hairline.
It is mainly used by optometrists and opticians to measure the back or front vertex power of a spectacle lens and verify the correct prescription in a pair of eyeglasses, to properly orient and mark uncut lenses, and to confirm the correct mounting of lenses in spectacle frames.
Shape from focus or shape from defocus is a method of 3D reconstruction which consists of the use of information about the focus of an optical system to provide a means of measurement for 3D information. [1]
In order to get repeatable, accurate measurements, it is important that the instrument stays focused. It uses the Scheiner principle, common in autofocus devices, in which the converging reflected rays coming towards the eyepiece are viewed through (at least) two separate symmetrical apertures.