Autofocus On Lens And Autofocus On Camera?

Optical system to focus on an automatically or manually selected point or surface area

For the pic of the same name, come across Auto Focus.

Several green focus points/areas indicating where the autofocus has locked

I selected green focus point using pinpoint autofocus

An autofocus (or AF) optical system uses a sensor, a command system and a motor to focus on an automatically or manually selected bespeak or expanse. An electronic rangefinder has a display instead of the motor; the adjustment of the optical arrangement has to exist washed manually until indication. Autofocus methods are distinguished as active, passive or hybrid types.

Autofocus systems rely on one or more sensors to determine right focus. Some AF systems rely on a unmarried sensor, while others use an array of sensors. Most modern SLR cameras apply through-the-lens optical sensors, with a split sensor array providing lite metering, although the latter can exist programmed to prioritize its metering to the same surface area equally i or more of the AF sensors.

Through-the-lens optical autofocusing is unremarkably speedier and more precise than manual focus with an ordinary viewfinder, although more than precise manual focus tin can be accomplished with special accessories such as focusing magnifiers. Autofocus accuracy within 1/3 of the depth of field (DOF) at the widest aperture of the lens is common in professional AF SLR cameras.

Nearly multi-sensor AF cameras allow transmission choice of the active sensor, and many offer automatic selection of the sensor using algorithms which endeavor to discern the location of the subject. Some AF cameras are able to discover whether the subject area is moving towards or away from the camera, including speed and acceleration, and proceed focus — a function used mainly in sports and other activeness photography. Canon cameras call this AI servo; Nikon cameras phone call it "continuous focus".

The information nerveless from AF sensors is used to command an electromechanical organisation that adjusts the focus of the optical system. A variation of autofocus is an electronic rangefinder, in which focus data are provided to the operator, but adjustment of the optical organisation is still performed manually.

The speed of the AF system is highly dependent on the widest aperture offered by the lens at the current focal length. F-stops of around f/2 to f/2.8 are generally considered best for focusing speed and accuracy. Faster lenses than this (e.g.: f/1.4 or f/ane.8) typically have very low depth of field, meaning that it takes longer to attain correct focus, despite the increased corporeality of calorie-free. Most consumer camera systems volition only autofocus reliably with lenses that take a widest discontinuity of at least f/5.6, whilst professional models tin can ofttimes cope with a widest aperture of f/8, which is especially useful for lenses used in conjunction with teleconverters.^{[ commendation needed ]}

History [edit]

Between 1960 and 1973, Leitz (Leica)^[1] patented an assortment of autofocus and corresponding sensor technologies. At photokina 1976, Leica had presented a photographic camera based on their previous development, named Correfot, and in 1978 they displayed an SLR camera with fully operational autofocus.

The get-go mass-produced autofocus camera was the Konica C35 AF, a simple point and shoot model released in 1977. The Polaroid SX-lxx Sonar OneStep was the starting time autofocus unmarried-lens reflex camera, released in 1978.

The Pentax ME-F, which used focus sensors in the photographic camera body coupled with a motorized lens, became the first autofocus 35 mm SLR in 1981.

In 1983 Nikon released the F3AF, their start autofocus camera, which was based on a similar concept to the ME-F.

The Minolta 7000, released in 1985, was the first SLR with an integrated autofocus system, significant both the AF sensors and the bulldoze motor were housed in the camera trunk, as well as an integrated film advance winder — which was to become the standard configuration for SLR cameras from this manufacturer, and likewise Nikon abased their F3AF system and integrated the autofocus-motor and sensors in the body.

Canon decided to discontinue their FD mount and switched to the completely electronic EF mount with motorised lenses in 1987.

Pentax was the outset to introduce focusing distance measurement for SLR cameras with the FA and FA* series lenses from 1991. Their first K_AF-mount Pentax lenses with AF had been introduced in 1989.^[2]

In 1992, Nikon changed back to lens integrated motors with their AF-I and AF-Southward range of lenses; today their entry-level DSLRs do not have a focus motor in the trunk due to the availability of motors in all new developed AF-Lenses.

Active [edit]

Active AF systems measure altitude to the subject independently of the optical arrangement, and afterwards adjust the optical system for correct focus.

In that location are various means to measure distance, including ultrasonic sound waves and infrared calorie-free. In the first case, sound waves are emitted from the camera, and past measuring the delay in their reflection, distance to the subject is calculated. Polaroid cameras including the Spectra and SX-70 were known for successfully applying this organization. In the latter case, infrared light is usually used to triangulate the distance to the subject area. Compact cameras including the Nikon 35TiQD and 28TiQD, the Canon AF35M, and the Contax T2 and T3, as well as early video cameras, used this organization. A newer approach included in some consumer electronic devices, similar mobile phones, is based on the time-of-flight principle, which involves shining a laser or LED calorie-free to the subject field and computing the distance based on the time it takes for the low-cal to travel to the field of study and back. This technique is sometimes called laser autofocus, and is nowadays in many mobile phone models from several vendors. It is also present in industrial and medical^[iii] devices.

An exception to the 2-stride approach is the mechanical autofocus provided in some enlargers, which accommodate the lens directly.

Passive [edit]

Passive AF systems make up one's mind correct focus by performing passive analysis of the image that is entering the optical system. They generally practice not direct any energy, such as ultrasonic sound or infrared light waves, toward the subject. (Even so, an autofocus assist beam of unremarkably infrared light is required when in that location is not enough light to accept passive measurements.) Passive autofocusing can exist accomplished by phase detection or contrast measurement.

Phase detection [edit]

Phase detection: In each figure (not to scale), the surface area within the regal circle represents the object to be focused on, the ruddy and green lines represent light rays passing through apertures at the contrary 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 assortment. Figures 1 to iv represent conditions where the lens is focused (ane) too nigh, (2) correctly, (3) also far and (four) much too far. The phase difference betwixt the two profiles can be used to decide in which direction and how much to move the lens to achieve optimal focus.

Phase detection (PD) is accomplished past dividing the incoming light into pairs of images and comparing them. Through-the-lens secondary paradigm registration (TTL SIR) passive phase detection is oftentimes used in picture and digital SLR cameras. The system uses a axle splitter (implemented as a minor semi-transparent area of the main reflex mirror, coupled with a minor secondary mirror) to direct low-cal to an AF sensor at the lesser of the photographic 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 uncomplicated rangefinder with a base within the lens's diameter. The two images are then analysed for similar low-cal intensity patterns (peaks and valleys) and the separation fault 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 corporeality of focus-ring motility.^[4]

PD AF in a continuously focusing fashion (e.g. "AI Servo" for Catechism, "AF-C" for Nikon, Pentax and Sony) is a airtight-loop control procedure. PD AF in a focus-locking mode (e.g. "One-Shot" for Canon, "AF-S" for Nikon and Sony) is widely believed to be a "one measurement, i move" open up-loop control process, but focus is confirmed simply when the AF sensor sees an in-focus subject. The only apparent differences betwixt 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 aforementioned closed-loop process.^[5]

Although AF sensors are typically one-dimensional photosensitive strips (only a few pixels high and a few dozen wide), some modern cameras (Canon EOS-1V, Canon EOS-1D, Nikon D2X) feature TTL surface area SIR^{[ citation needed ]} sensors that are rectangular in shape and provide two-dimensional intensity patterns for a finer-grain assay. Cantankerous-type focus points have a pair of sensors oriented at 90° to 1 another, although one sensor typically requires a larger discontinuity to operate than the other.

Some cameras (Minolta seven, Canon EOS-1V, 1D, 30D/40D, Pentax M-1, Sony DSLR-A700, DSLR-A850, DSLR-A900) as well have a few "high-precision" focus points with an additional gear up of prisms and sensors; they are merely active with "fast lenses" with sure geometrical apertures (typically f-number 2.8 and faster). Extended precision comes from the wider effective measurement base of the "range finder".

Stage detection organization: 7 – Optical system for focus detection; 8 – Image sensor; xxx – Plane of the vicinity of the exit pupil of the optical system for photography; 31, 32 – Pair of regions; 70 – Window; 71 – Visual field mask; 72 – Condenser lens; 73, 74 – Pair of apertures; 75 – Discontinuity mask; 76, 77 – Pair of reconverging lenses; 80, 81 – Pair of lite receiving sections

Contrast detection [edit]

Contrast-detection autofocus is achieved by measuring Contrast (vision) within a sensor field through the lens. The intensity difference between adjacent pixels of the sensor naturally increases with right image focus. The optical system can thereby be adjusted until the maximal contrast is detected. In this method, AF does not involve actual altitude measurement at all. This creates significant challenges when tracking moving subjects, since a loss of dissimilarity gives no indication of the management of motion towards or away from the camera.

Contrast-detect autofocus is a common method in digital cameras that lack shutters and reflex mirrors. Most DSLRs utilize this method (or a hybrid of both dissimilarity and phase-detection autofocus) when focusing in their live-view modes. A notable exception is Canon digital cameras with Dual Pixel CMOS AF. Mirrorless interchangeable-lens cameras typically used contrast-measurement autofocus, although phase detection has get the norm on most mirrorless cameras giving them significantly ameliorate AF tracking performance compared to contrast detection.

Contrast detection places different constraints on lens design when compared with phase detection. While stage detection requires the lens to move its focus bespeak quickly and directly to a new position, contrast-detection autofocus instead employs lenses that can quickly sweep through the focal range, stopping precisely at the point where maximal contrast is detected. This ways that lenses designed for phase detection often perform poorly on camera bodies that use contrast detection.

Assist lamp [edit]

The assist lite (also known every bit AF illuminator) "activates" passive autofocus systems in depression-light and low-contrast situations in some cameras. The lamp projects visible or IR lite onto the bailiwick, which the camera's autofocus system uses to attain focus.

Many cameras and most all camera phones^[a] lack a dedicated autofocus assistance lamp. Instead, they employ their congenital-in wink, illuminating the subject field with bursts of light. This aids the autofocus system in the same fashion as a dedicated assist light, but has the disadvantage of startling or abrasive people. Another disadvantage is that if the photographic camera uses flash focus assist and is set to an performance style that overrides the flash, it may as well disable the focus assist. Thus, autofocus may fail to acquire the subject.

Like stroboscopic flashing is sometimes used to reduce the blood-red-eye effect, but this is simply intended to constrict the subject's centre pupils before the shot.

Some external flash guns take integrated autofocus assistance lamps that replace the stroboscopic on-photographic camera flash. Many of them are cherry-red and less obtrusive. Another way to aid contrast based AF systems in depression lite is to beam a laser pattern on to the subject. The light amplification by stimulated emission of radiation method is commercially called Hologram AF Light amplification by stimulated emission of radiation and was used in Sony CyberShot cameras effectually the twelvemonth 2003, including Sony's F707, F717 and F828 models.

Hybrid autofocus [edit]

In a hybrid autofocus organization, focus is achieved by combining 2 or more methods, such every bit:

• Active and passive methods
• Stage detection and dissimilarity measurement

The double effort is typically used to mutually compensate for the intrinsical weaknesses of the various methods in society to increase the overall reliability and accuracy or to speed up AF function.

A rare example of an early hybrid system is the combination of an active IR or ultrasonic motorcar-focus system with a passive stage-detection arrangement. An IR or ultrasonic system based on reflection will piece of work regardless of the light conditions, but tin can exist easily fooled by obstacles like window glasses, and the accurateness is typically restricted to a rather express number of steps. Phase-detection autofocus "sees" through window glasses without issues and is much more accurate, but it does not work in depression-light conditions or on surfaces without contrasts or with repeating patterns.

A very mutual example of combined usage is the phase-detection motorcar-focus system used in unmarried-lens reflex cameras since the 1985s. The passive phase-detection motorcar-focus needs some contrast to work with, making it difficult to use in low-light scenarios or on fifty-fifty surfaces. An AF illuminator volition illuminate the scene and project contrast patterns onto even surfaces, and then that phase-detection automobile-focus can work nether these atmospheric condition as well.

A newer class of a hybrid system is the combination of passive stage-detection auto-focus and passive contrast motorcar-focus, sometimes assisted past active methods, as both methods need some visible contrast to piece of work with. Under their operational weather, stage-detection auto-focusing is very fast, since the measurement method provides both information, the amount of beginning and the direction, so that the focusing motor can movement the lens correct into (or close to) focus without boosted measurements. Additional measurements on the fly, however, can improve accuracy or help keep runway of moving objects. Yet, the accuracy of phase-detection auto-focus depends on its effective measurement footing. If the measurement basis is large, measurements are very authentic, but tin can merely work with lenses with a large geometrical discontinuity (e.g. 1:2.8 or larger). Even with high contrasty objects, phase-detection AF cannot piece of work at all with lenses slower than its effective measurement basis. In order to work with most lenses, the effective measurement footing is typically prepare to between ane:v.6 and 1:half dozen.7, then that AF continues to work with slow lenses (at to the lowest degree for every bit long as they are not stopped downwardly). This, however, reduces the intrinsical accuracy of the autofocus system, even if fast lenses are used. Since the effective measurement basis is an optical holding of the actual implementation, it cannot be changed hands. Very few cameras provide multi-PD-AF systems with several switchable measurement bases depending on the lens used in society to allow normal auto-focusing with almost lenses, and more accurate focusing with fast lenses. Contrast AF does not have this inherit design limitation on accuracy as information technology only needs a minimal object dissimilarity to work with. Once this is available, it can work with high accuracy regardless of the speed of a lens; in fact, for as long as this status is met, it tin even work with the lens stopped down. Also, since contrast AF continues to piece of work in stopped-down way rather than only in open-aperture manner, information technology is allowed to discontinuity-based focus shift errors phase-detection AF systems suffer since they cannot piece of work in stopped-down manner. Thereby, contrast AF makes arbitrary fine-focus adjustments by the user unnecessary. Also, contrast AF is allowed to focusing errors due to surfaces with repeating patterns and they can work over the whole frame, non just near the heart of the frame, as phase-detection AF does. The down-side, even so, is that contrast AF is a closed-loop iterative procedure of shifting the focus back and along in rapid succession. Compared to phase-detection AF, contrast AF is slow, since the speed of the focus iteration process is mechanically express and this measurement method does not provide whatsoever directional information. Combining both measurement methods, the phase-detection AF tin can assist a contrast AF system to be fast and authentic at the same time, to compensate aperture-based focus-shift errors, and to continue to work with lenses stopped downward, equally, for example, in stopped-downward measuring or video mode.

Recent developments towards mirrorless cameras seek to integrate the phase-detection AF sensors into the image sensor itself. Typically, these phase-detection sensors are not as authentic as the more than sophisticated stand-alone sensors, but since the fine focusing is now carried out through contrast focusing, the stage-detection AF sensors are only need to provide coarse directional data in order to speed up the contrast auto-focusing process.

In July, 2010, Fujifilm announced a meaty photographic camera, the F300EXR, which included a hybrid autofocus organisation consisting of both phase-detection and contrast-based elements. The sensors implementing the phase-detection AF in this photographic camera are integrated into the photographic camera's Super CCD EXR.^[6] Currently information technology is used past Fujifilm FinePix Serial,^[7] Fujifilm X100S, Ricoh, Nikon 1 series, Canon EOS 650D/Rebel T4i and Samsung NX300.

Comparison of active and passive systems [edit]

Active systems will typically not focus through windows, since sound waves and infrared light are reflected past the glass. With passive systems this volition generally not be a problem, unless the window is stained. Accuracy of active autofocus systems is often considerably less than that of passive systems.

Active systems may also neglect to focus a subject that is very close to the camera (e.g., macro photography).

Passive systems may not find focus when the dissimilarity is depression, notably on large single-colored surfaces (walls, blue sky, etc.) or in low-light conditions. Passive systems are dependent on a certain degree of illumination to the subject field (whether natural or otherwise), while active systems may focus correctly even in full darkness when necessary. Some cameras and external flash units take a special depression-level illumination fashion (usually orangish/red light) which can be activated during auto-focus operation to allow the camera to focus.

• 

  Active autofocus organization via infrared - Catechism AF35M (1979)

• 

  Early passive autofocus organization integrated in the lens with Pentax ME-F (1981)

• 

  Modern (2014) autofocus unmarried lens reflex camera

Trap focus [edit]

A method variously referred to as trap focus, focus trap, or catch-in-focus uses autofocus to take a shot when a subject moves into the focal plane (at the relevant focal betoken); this can be used to get a focused shot of a rapidly moving object, particularly in sports or wild animals photography, or alternatively to set a "trap" so that a shot can automatically be taken without a person present. This is done past using AF to observe but not set up focus – using manual focus to set focus (or switching to manual after focus has been ready) but then using focus priority to find focus and simply release the shutter when an object is in focus. The technique works by choosing the focus aligning (turning AF off), then setting the shooting mode to "Single" (AF-S), or more than specifically focus priority, then depressing the shutter – when the subject moves into focus, the AF detects this (though it does not alter the focus), and a shot is taken.^{[viii] [9] [10]}

The first SLR to implement trap focusing was the Yashica 230 AF. Trap focus is also possible on some Pentax (eastward.one thousand. K-ten and K-five), Nikon, and Canon EOS cameras. The EOS 1D can exercise it using software on an attached figurer, whereas cameras similar the EOS 40D and 7D have a custom function (3-1 and III-4 respectively) which tin end the camera trying to focus subsequently it fails.^{[ citation needed ]} On EOS cameras without 18-carat trap focus, a hack called "almost trap focus" can be used, which achieves some of the effects of trap focus.^[11] By using the custom firmware Magic Lantern, some Canon DSLRs can perform trap focus.

AI Servo [edit]

AI Servo is an autofocus mode found on Canon SLR cameras, and in other brands such as Nikon, Sony, and Pentax, nether the proper name "continuous focus" (AF-C).^[12] Too referred to equally focus tracking, information technology is used to runway a subject area as it moves around the frame, or toward and abroad from the camera. When in use, the lens will constantly maintain its focus on the subject, hence information technology is unremarkably used for sports and action photography. AI refers to bogus intelligence: algorithms that constantly predict where a subject is about to be based on its speed and acceleration data from the autofocus sensor.

Focus motors [edit]

Modern autofocus is washed through one of two mechanisms; either a motor in the camera torso and gears in the lens ("screw drive") or through electronic transmission of the drive instruction through contacts in the mount plate to a motor in the lens. Lens-based motors can exist of a number of different types, but are ofttimes ultrasonic motors or stepper motors.

Some camera bodies, including all Catechism EOS bodies and the more than budget-oriented amongst Nikon'due south DX models, practise not include an autofocus motor and therefore cannot autofocus with lenses that lack an inbuilt motor. Some lenses, such every bit Pentax' DA* designated models, although normally using an inbuilt motor, tin can fall back to screwdrive operation when the photographic camera body does not support the necessary contact pins.

Notes [edit]

1. ^ Counter-examples are the Nokia Lumia 1020, the Samsung Galaxy S4 Zoom and the Samsung Galaxy Chiliad Zoom.

See also [edit]

Wikimedia Commons has media related to Autofocus.

• Circular polarizer, the only polarizer to work with some SLR autofocusers
• Fixed-focus lens
• List of Nikon compatible lenses with integrated autofocus-motor
• Manual focus override
• Lite-field camera, a photographic camera that enables focusing in a postprocessing stride

References [edit]

1. ^ "S Organisation: Autofocus – Leica Fotografie International". Archived from the original on 2009-06-21. Retrieved 2009-05-15 .
2. ^ "Milestones - Asahi Optical Historical Club". Retrieved 2021-08-29 .
3. ^ Fricke, Dierk; Denker, Evgeniia; Heratizadeh, Annice; Werfel, Thomas; Wollweber, Merve; Roth, Bernhard (28 May 2019). "Non-Contact Dermatoscope with Ultra-Brilliant Lite Source and Liquid Lens-Based Autofocus Function". Practical Sciences. 9 (11): 2177. doi:10.3390/app9112177.
4. ^ "Nikon - Engineering science - Predictive Focus Tracking System". Archived from the original on 2013-11-12. Retrieved 2013-eleven-12 .
5. ^ "Busted! The Myth of Open up-loop Stage-detection Autofocus".
6. ^ Fujifilm Launches Powerhouse 15X Long Zoom Point and shoot Digital Camera: The FinePix F300EXR, Fujifilm, United states
7. ^ "Fujifilm launches FinePix HS50EXR and HS35EXR high-end superzooms". Retrieved June 8, 2013.
8. ^ Trap Focus for Nikon Users, past Kenneth William Caleno, January 28, 2009
9. ^ How to shoot sport, Ken Rockwell, 2006
10. ^ Focus Trap or Catch In Focus, Apr 4, 2009
11. ^ EOS Documentation Project: About Trap Focus Archived August 18, 2010, at the Wayback Machine, by Julian Loke
12. ^ "Articles tagged "learn": Digital Photography Review".

External links [edit]

• interactive Flash demo showing how phase detection autofocus works.
• interactive Flash demo showing how contrast detection autofocus works.
• How Stuff Works – Autofocus
• Canon EOS DSLR Autofocus Explained

Source: https://en.wikipedia.org/wiki/Autofocus

Posted by: yosthister.blogspot.com

Share this post