Autofocus Wikipedia. An autofocus or AF optical system uses a sensor, a control system and a motor to focus on an automatically or manually selected point or area. An electronic rangefinder has a display instead of the motor the adjustment of the optical system has to be done manually until indication. Autofocus methods are distinguished by their type as being either active, passive or hybrid variants. Ujx8LFb7Sw/UpHE9RqlcJI/AAAAAAAADpY/KsVB9P0kL7g/s1600/e-thesis+055.jpg' alt='Pentax Me Super Winder Manual Transmission' title='Pentax Me Super Winder Manual Transmission' />GeneraleditAutofocus systems rely on one or more sensors to determine correct focus. Some AF systems rely on a single sensor, while others use an array of sensors. Most modern SLR cameras use through the lens optical AF sensors, with a separate sensor array providing light metering, although the latter can be programmed to prioritize its metering to the same area as one or more of the AF sensors. Through the lens optical autofocusing is now often speedier and more precise than can be achieved manually with an ordinary viewfinder, although more precise manual focus can be achieved with special accessories such as focusing magnifiers. Autofocus accuracy within 13 of the depth of field DOF at the widest aperture of the lens is common in professional AF SLR cameras. Most multi sensor AF cameras allow manual selection of the active sensor, and many offer automatic selection of the sensor using algorithms which attempt to discern the location of the subject. Collectible photographic materials, including worlds largest assortment of instruction manuals. Some AF cameras are able to detect whether the subject is moving towards or away from the camera, including speed and acceleration data, and keep focus on the subject  a function used mainly in sports and other action photography on Canon cameras this is known as AI servo, while on Nikon cameras it is known as continuous focus. The data collected from AF sensors is used to control an electromechanical system that adjusts the focus of the optical system. A variation of autofocus is an electronic rangefinder, a system in which focus data are provided to the operator, but adjustment of the optical system is still performed manually. The speed of the AF system is highly dependent on the widest aperture offered by the lens. F stops of around f2 to f2. Faster lenses than this e. Most consumer camera systems will only autofocus reliably with lenses that have a widest aperture of at least f5. HistoryeditBetween 1. Leitz Leica1 patented an array of autofocus and corresponding sensor technologies. At photokina 1. 97. Leica had presented a camera based on their previous development, named Correfot, and in 1. SLR camera with fully operational autofocus. The first mass produced autofocus camera was the Konica C3. AF, a simple point and shoot model released in 1. The Polaroid. SX 7. Sonar One. Step was the first autofocus single lens reflex camera, released in 1. The Pentax ME F, which used focus sensors in the camera body coupled with a motorized lens, became the first autofocus 3. SLR in 1. 98. 1. In 1. C400&ssl=1' alt='Pentax Me Super Winder Manual Transmission' title='Pentax Me Super Winder Manual Transmission' />Nikon released the F3. AF, their first autofocus camera, which was based on a similar concept to the ME F. The Minolta 7. 00. SLR with an integrated autofocus system, meaning both the AF sensors and the drive motor were housed in the camera body, as well as an integrated film advance winder  which was to become the standard configuration for SLR cameras from this manufacturer, and also Nikon abandoned their F3. AF system and integrated the autofocus motor and sensors in the body. Search the worlds information, including webpages, images, videos and more. Google has many special features to help you find exactly what youre looking for. Even more Account Options. Sign in Search settings. Argus Canon Chinon Edixa Exakta Kodak Konica Mamiya Minolta Miranda Nikon Olympus Pentacon Pentax Petri Praktica Ricoh Topcon. Misc Up. 0 125 bler heck industries TB400 tubing 0. TB400 tubing 0 125 notcher comaca n 225 epas 0. Canon, however, elected to develop their EOS system with motorised lenses instead. In 1. 99. 2, Nikon changed back to lens integrated motors with their AF I and AF S range of lenses today their entry level DSLRs do not have a focus motor in the body due to a broad range of available lenses with internal focus motors. Active AF systems measure distance to the subject independently of the optical system, and subsequently adjust the optical system for correct focus. There are various ways to measure distance, including ultrasonic sound waves and infrared light. In the first case, sound waves are emitted from the camera, and by measuring the delay in their reflection, distance to the subject is calculated. Polaroid cameras including the Spectra and SX 7. In the latter case, infrared light is usually used to triangulate the distance to the subject. Compact cameras including the Nikon 3. Ti. QD and 2. 8Ti. QD, the Canon AF3. M, and the Contax T2 and T3, as well as early video cameras, used this system. A newer approach included in some consumer electronic devices, like mobile phones, is based on the time of flight principle, which involves shining a laser or LED light to the subject and calculating the distance based on the time it takes for the light to travel to the subject and back. This technique is sometimes called laser auto focus, and is present in many mobile phone models from several vendors. An exception to the two step approach is the mechanical autofocus provided in some enlargers, which adjust the lens directly. PassiveeditPassive AF systems determine correct focus by performing passive analysis of the image that is entering the optical system. They generally do not direct any energy, such as ultrasonic sound or infrared light waves, toward the subject. However, an autofocus assist beam of usually infrared light is required when there is not enough light to take passive measurements. Passive autofocusing can be achieved by phase detection or contrast measurement. Phase detectionedit. Phase detection In each figure not to scale, the purple circle represents the object to be focused on, the red and green lines represent light rays passing through apertures at the opposite sides of the lens, the yellow rectangle represents sensor arrays one for each aperture, and the graph represents the intensity profile as seen by each sensor array. Figures 1 to 4 represent conditions where the lens is focused 1 too near, 2 correctly, 3 too far and 4 much too far. How To Program A 2008 Saturn Aura Key Fob on this page. The phase difference between the two profiles can be used to determine in which direction and how much to move the lens to achieve optimal focus. Phase detection PD is achieved by dividing the incoming light into pairs of images and comparing them. Through the lens secondary image registration TTL SIR passive phase detection is often used in film and digital SLR cameras. The system uses a beam splitter implemented as a small semi transparent area of the main reflex mirror, coupled with a small secondary mirror to direct light to an AF sensor at the bottom of the camera. Two micro lenses capture the light rays coming from the opposite sides of the lens and divert it to the AF sensor, creating a simple rangefinder with a base within the lenss diameter. The two images are then analysed for similar light intensity patterns peaks and valleys and the separation error is calculated in order to find whether the object is in front focus or back focus position. This gives the direction and an estimate of the required amount of focus ring movement. PD AF in a continuously focusing mode e. AI Servo for Canon, AF C for Nikon, Pentax and Sony is a closed loop control process. PD AF in a focus locking mode e. One Shot for Canon, AF S for Nikon and Sony is widely believed to be a one measurement, one movement open loop control process, but focus is confirmed only when the AF sensor sees an in focus subject. The only apparent differences between the two modes are that a focus locking mode halts on focus confirmation, and a continuously focusing mode has predictive elements to work with moving targets, which suggests they are the same closed loop process. Although AF sensors are typically one dimensional photosensitive strips only a few pixels high and a few dozen wide, some modern cameras Canon EOS 1. V, Canon EOS 1. D, Nikon D2. X feature TTL area SIRcitation needed sensors that are rectangular in shape and provide two dimensional intensity patterns for a finer grain analysis. Cross type focus points have a pair of sensors oriented at 9.