Auto Focus Introduction

Af:auto Focus Autofocus

Pdaf:phase Detection AF Phase Focus

Caf:contrast Detection Contrast Focus/contrast focus (continuous shooting with a certain step, select a large position of contrast value)

Transferred from: http://www.jianshu.com/p/1ccbaf458354

Autofocus (auto focus) is a technology developed in the the 1960s and is used primarily in cameras and other optical devices. Many technologies are needed, such as semiconductors, optoelectronics, Micro motors and other support.

It has been a huge wave since it was applied to civilian cameras in the the 1970s, and today, from compact digital cameras to SLR or non-inverting models, it's almost all over autofocus.

Taking photos today does not need to know so many principles, this note as a byproduct of the wiki article, briefly introduce the development of autofocus and the status quo, for interested friends reference.

background

The so-called focus is the drive of one or more of the optical lens, and the process of obtaining the clearest image of a focusing or imaging element has a history even earlier than the birth of the camera-early painters have a focus concept when they have a "framing box". And the camera in the Daguerre era after the invention of the rapid development of the photographer, from the wet version to the film, from a single black and white photography to obtain color, manual metering to automatic metering, finally, the need for autofocus day came.

Before the advent of AF, there are two ways to focus manually, one is the rangefocus (scale focus), the other is the viewfinder linkage focus, both of which are mentioned later in this article, the former is limited in accuracy, the latter is of various shapes, such as macular and crack, But for the user's eyes and operation have certain requirements, but also limits the camera This "magic box" in the general public-the masses have requirements, engineers will naturally find ways to solve.

Interestingly, the earliest available record was the auto-focus-related patent proposed by Leica, which was filed almost in the 60 's ~1973 (I found the link to the English wiki invalid when I was transporting it, and I lamented that the information of this era has gone faster.) Related to the past mentioned here).

Leica is the inventor of the 135 camera, for a long time, and even now, arguably the undisputed 135 kings; technology leadership and manufacturing excellence are their trump cards. This kind of enterprise wants to set off a new wave, also completely understandable. At the 1976 Photokina exhibition, Leica has also launched a concept product Correfot, which later shows the full-featured AF SLR for 78 years ... Then, then, there was no more. Auto-focus machine to wait until 21st century and Panasonic after the introduction of several OEM DC; perhaps worth mentioning the 2006 Digilux 3,43 photosensitive element of the convertible lens model ( but in fact, Olympus E-330 modification, Panasonic L1 re-OEM ). Then there is the x1/x2,aps-c T-system of the test water, and the 2015 LEICAQ, but this is something.

It's nothing to do with graphics, I just put a Leica town building (Leica I)

Blossoming, the Japanese camera industry in the 70-80 's generation has a trend behind the momentum. In other words, the people want to be the ultimate picture quality and balance of the function, the former Japanese chase, it seems to be almost the meaning, the latter is in the auto-focus on the field of Fame. The C35 af of the 77 Konica (Konica) is an autofocus PS machine, while the 81 Pentax Me-f extends autofocus to the SLR field. The 1985 Minolta Minoltaaf was also a milestone, announcing the emergence of a truly complete autofocus system. Although the α7000 can be said to be mediocre, even on the withdrawal of the wheel and the use of slender button design is limited to the aesthetic mark of the times, but ultimately all kinds of technical synthesis. Pentax (Pentax), Nikon (Nikon) and Canon have also invested in new markets.

The United States is not weida at this time, except that Vivitar is passionate about computer-aided design, and a Polaroid (Polaroid) company has been passionate about instant (instant imaging) The SX-70 series produced in the ~81 of 72 was the leader in its products, and the OneStep model, which was produced in 78, also had a sonar autofocus system. For a moment, Disneyland, instant imaging, fool operation, is undoubtedly a specific image of the American Dream.

Another giant in Germany, Carl Zeiss, in the 90 's may be the German reunification, everything can be a good encouragement, but also United Japan Kyocera launched the auto-focus of the Contax brand products, non-change the lens of the T-system, can change the lens of the G series and later N-series SLR products.

As the Times advance, autofocus technology is also developing, but not in the "background" chapter. The last thing to say is that, in the early 90 of the 80, Honeywell, the American company, sued Minolta (Minolta) for patent infringement on autofocus, which was just the end of Japan's bubble economy, and the U.S. In short, Minolta was defeated by the U.S. court, compensation for about 120 million dollars (well, the early 90 "billion dollars"); the financial crisis led to a lot of things later, can be written separately. (Interested friends can also take the initiative to read the Japanese article "ミノルタ?ハネウェル to Litigation")

Principle and realization

From a deconstruction point of view, autofocus can actually be seen as the automation of manual focus: Turning the focusing ring (to drive the focus lens), observing the viewfinder, and observing that the focal point stops focusing.

There is another manual focus method (using a rangefinder or an estimate) to measure the distance from the camera film to the body, and then rotate the focusing ring according to the lens ruler. This method, known as the scale focus, is less used with the popularity of macular focus and SLR cameras, and occasionally in humanities photography with the focus of the zoom.

These two methods seem to correspond to the two main categories of autofocus, namely "passive" and "active".

Active Type

To put it simply, the active autofocus is to take a rangefinder, gesturing about the center of the picture, measured to distance data, passed to the fuselage, the body according to the ruler push the focus lens to that position, "click", take a photo of the focus success. Based on this, "active" is called "ranging" may be more like some.

Polaroid SX-70 sonar OneStep, sonar is bigger than the camera.

The advantage is obvious, is the body of the internal imaging structure of the basic do not change, add an external accessory and then communicate and drive the lens is. So, in the early days of autofocus, many of these designs were, for example, the sonar onestep in the Polaroid SX-70 series.

The specific implementation of the rangefinder, ultrasonic (sonar), infrared, and the recent paragraph, re-turned on the mobile phone used as a gimmick of "laser focus", are similar.

Contax G, auto-focus side-axis system, small forehead window is used for infrared ranging. Exceptions to the following statements

As to the right on the right, sorry, the general model of the viewfinder can not be seen, I want to focus on the more special points in the screen, sorry, not very good choice. These problems, as well as the large volume of the early external rangefinder, all affected the camera design (in the case of infrared window ranging, an exception, the degree of compactness, in the end of 20th century is generally equipped with shoot camera). Because of the lack of active ranging type, there is the following passive.

Passive

In fact, think carefully to "passive" this statement is not rigorous, strictly speaking, this is called TTL type. The so-called TTL, is Through the abbreviation of the Lens, literal literal translation "through the Lens", free translation "mirror"; before autofocus, this is used to distinguish the mode of call metering, and now it is autofocus.

The "mirror" behavior, the advantage is "WYSIWYG", from the elimination of parallax, accurate metering, to autofocus, no one is not so, and can be operated in the mirror mode of the camera system, at that time is a single-lens reflective frame model, namely the so-called "SLR."

In this mirror, the passive autofocus is divided into two implementations, namely "phase focus" and "contrast focus". These two implementations are related to image sensor technology, which has been developed earlier.

phase Focus (Phase Detection Auto Focus,PDAF), which may also be called "Phase difference Focus", is to place the sensor under "Diggers snaking along", It then captures the way the light from the different edges of the lens is detected on this line. It's more complicated, and it's easy to see.

Phase focus, different position conditions

This figure is the most concise picture of the principle I have seen, from DP Review, made a good move to insert the article. Here the sensor is the phase focus sensor, for the transverse distribution, the red and blue lines represent the lens of the same subject through the lens of the projection of light, coincident is the focal point, and if not coincident, but also according to the specific distribution location, the direction of the focus deviation can be determined to facilitate the feedback correction.

The wise reader would have thought, too, if the word was just in the same direction as the fringe of the object, wouldn't it be flying blind? In order to solve this problem, the original Higo changed to cross or X-word array can be, in the United States can reach Dynax 7 (that is, A7) released (about 2000 years), there is also a "double cross" argument, in fact, the sensor arrangement with "Ten" overlay "X", but may be called " M-word focus "is not good to listen (" Double cross "more Cool no!) ）。 Mowgli's Xitek West old year also wrote a "double cross-sensor principle", welcome to read.

contrast Focus (contrast Detection Auto focus,Cdaf), also known as "contrast Focus", is a method of judging the focal condition based on the contrast of the object in the picture. So consider that this focus is done with the sensor as the framing/imaging condition.

Such a discriminant method, closer to the human judgment process, that is, to observe the picture changes to make the next decision. However, to simulate such a process, the image recognition, drive algorithm, as well as the support of the chip and so on have higher requirements; when the civil compact digital camera first appeared, such a focus is slow compared with the development of the SLR for many years of phase focus, the development of technology allows the speed of contrast focus, especially in micro After the launch of the 4/3 system, the contrast-focused speed was even more than some SLR cameras, with the efforts of Olympus and Panasonic as the business representatives. The "Focus speed" section later says.

Changes from real-time framing

Since 2006, with the Olympus E-330 as the representative, the real real-time viewing function (live View) has been introduced into the large-base sensor model, its convenience has been deeply rooted (especially the new users). In the new era, more and more use of the sensor framing shooting situation, however, the structure of the SLR (later "run" paragraph will be mentioned) decided to lift the reflector can not enable phase focus. In order to solve this problem, at this time the manufacturers, proposed two kinds of solutions:
1. When lifting the reflector, use contrast to focus;
2. The first one is too slow, play some other tricks.

The former one can be considered Canon's EOS 450D as the representative, in Live view mode, using contrast focus; Of course, the people who used to understand how a slow process. The latter is represented by Olympus E-330 and Sony's α300/α350.

Olympus E-330 offers two modes of choice; A-mode is fast and practical and enables high-speed autofocus
Real-time framing of Sony α350

The latter scheme, when starting real-time framing, does not lift the reflector completely, but slightly changes the light path, projecting some of the mirror rays onto a slightly smaller pair of sensors; the rest of the light goes to the original phase sensor.

Sony further in 2010, in its release in the year of the SLT model, set a fixed translucent mirror, Sony called "Translucent Mirror Technology", the upper right corner with a TM angle. In this way, both framing and imaging use the main sensor, but the use of light is slightly less efficient than the SLR model.

This part of the content, I earlier in the "Olympus E-330" "Translucent Mirror" "Sony SLT Model" entry, for reference.

Mix and match, work not tired

Originally imaging film, auto-focus with CCD, it is natural to separate; now the imaging and autofocus are all ccd/cmos, so can they fit together?

It is such a simple idea, the birth of "sensor embedded phase focus" design. The first to produce such a sensor is Japan's Fujifilm, which launched the model "F300EXR" in 2010, with an embedded phase-focused EXR sensor.

The EXR sensor is a SUPERCCD-style hive arrangement with a yellow dot focusing

The specific implementation is to select a pair of pixels adjacent to the chip (here is the special hexagonal configuration of Fujifilm), each masking its half of the photosensitive, so that it can only accept the light from the opposite sides of the lens. Thus, the realization of the phase focusing module is achieved in principle. A video from Toshiba succinctly illustrates the problem.

Phase Focus and inline implementation

The theoretical disadvantage is that the points used as phase focus cannot participate in imaging and require in-machine processing to generate interpolation around the surrounding pixels; however, in today's tens of millions of pixels, the loss of several or even hundreds of pixels is really nothing compared to the convenience of this.

Canon's ability to focus on embedded phase points in the 650D era was lackluster, and in order to occupy the highlands in this wave of technology, it also introduced a full-pixel double-check coke (Dual Pixel CMOS AF) in the 70D generation, with complex names The fact is that two sets of diodes are placed on the pixel, so that the pixels can be either focused or imaged. Canon has introduced itself, and "firing pin" predecessors also have a "Canon Dual Pixel CMOS AF", although claiming to be a grass review, but it is specifically introduced in which the working principle, interested friends can step to read.

With the above-mentioned design, with the use of the sensor to view the contrast of the focus, the current commercial propaganda is often heard in the "hybrid focus", the usual practice is that the phase sensor detects the approximate focal position, the lens near the location, using a contrast method to further detect the Coke- In this way, the high-speed directivity characteristics of the phase difference method can be achieved, and the precision of contrast and the related pattern recognition ability are obtained. Fujifilm from the original EXR sensor, to now aps-c specifications of the x-transii have been equipped (it is said that the latter is a custom version of the Sony IMX071), and Nikon, Sony, Canon, Panasonic and other manufacturers are also in its non-anti-product added "hybrid focus" ranks.

Of course, the early phase of hybrid focus can also refer to early active and passive solutions, where space limitations are not introduced.

Related concepts

The principle is complete, and talk about some concepts related to autofocus.

Focus Speed

Here are a few things that affect the focus speed:
1. Focus mode and specific execution method
2. Sensitivity (sensor)
3. Motor (Actuator)
4. Lens arrangement

focus mode and algorithm , focusing mode selection, will affect the speed of autofocus. In the phase scheme, the sensor value of a single state can be used to determine the direction of the focus, while the contrast focus is obtained by the method of "try-observe (and analyze)-try again", which is restricted by the sensor sensitivity factor.

In terms of sensitivity, Nikon will name its phase-focus sensor (MULTI-CAM series) and, after some time, "devolve" the original high-order focus module to a new, lower-positioning model, a move that fans call kindness; Other companies do not seem to like this naming behavior, the auto-focus module upgrade is relatively unknown, but almost also follow the new technology must have an improved rhythm.

Nikon's high-end module, Multi-cam 3500fx,51 District

AF SLR Development Earlier there was a saying that That is, open aperture less than F5.6 lens can not achieve autofocus, in fact, is also related to the sensitivity of the sensor, and as an exception, the limit may be a Minolta 500R lens, the constant F8 aperture can still be in the reasonable design of the fuselage to achieve autofocus (only the center point, see the item "Up to 500R").

The contrast focusing algorithm has great influence. Last year I wrote an article about the Canon non-anti-EOS m introduction, do not want to cause the accidental vomit groove. "Chrysanthemum" (@ not spicy Rama) players, but also in the domestic, has been the first generation of models have carried out in-depth analysis, according to it, the EOS m on the contrast focusing algorithm such as X general-said this is full of resentment than eating a EOS m general.

Nikkei BP mentioned the first version of the focus algorithm, said "EOS m af is not simply" slow ", but let people" feel slow ". Canon also released a version of the upgrade firmware, 2.0.2, with user comparison found faster (YouTube video for proof). These are just to show that the hardware conditions are not changed, the rationalized algorithm can speed up the contrast focus.

What is the degree to which contrast focus can be achieved if more resources can be mastered? Canon's EOS m in 2012 was a negative example, while Olympus ' flagship model om-d E-M5, which was released in the same year, was pure contrast focusing, but at very high speeds. The company began to configure the e-p3 generation called "FAST AF" function, all known as frequency acceleration Sensor technology, the working mechanism is to 120FPS refresh rate analysis of the image, with a dedicated image processing chip, The changes in the image on the lens during focus movement become very sharp, combining the technology described later to achieve high-speed autofocus. In the 2014 after its birth, Panasonic's DFD (Depth from Defocus, Space-aware technology) and similar Sony 4D Focus developed the algorithm with a further recognition capability.

Sony 4D Focus Display

motor, lens or machine body of motor, although small, but to drive the movement of the lens, whether they are strong enough often determines the ability of the fuselage or lens, also affect the positioning in the market.

At the beginning of the development of the AF system, such as the Minolta system, the choice of the body to provide power-driven lens solution, because it can be single-body multi-lens multiplexing of the system, the cost is relatively low, but compared to a later launch, such as the Canon EOS system selected, the motor is placed in the lens approach, There are a lot of deficiencies (in the eyes of the present). In addition to commercial positioning considerations, the latter driving force and miniaturization can be developed at any time, while the former transmission chain long disadvantage has always existed. Nikon, Sony and Pentax are also transitioning from the latter in the field of SLR, while the non-inverting system exclusively the layout of the motor with the lens that was used in the first place.

Currently widely used in the lens of the motor, mainly ultrasonic motor and stepper motor (stepper motor).

The ultrasonic motor is a kind of miniature motor developed by using piezoelectric effect, that is, electric energy and mechanical energy interchange, it is interesting that its first commercial application and the most widely used is in the field of autofocus. Almost all camera manufacturers have their own ultrasonic motor technology, and have taken a complex commercial name, and then feel trouble and use three letters as an abbreviation (about good general, incredibly all three letters), very interesting.

The stepper motor in the real-time view gained popularity, also received attention, which is the contrast of the focus of the way and the way stepper motor work.

Canon Ef-m 22mm F2 STM lens mechanical structure diagram

Contrast focusing repeats the process of "analyzing sample-drive-Re-sampling", which is bound to regress the focus lens across the peak of the contrast; Stepping motors can be implemented more quickly because they can obtain their own morphological information without the need for other devices. Canon has been very respected USM ultrasonic motor, and large-scale assembly in the high-level lens, fans are also keen on this, however, in real-time framing and video large-scale application, but also have to compromise, in recent years, many of the lens assembly STM Motor came out, the essence is the stepper motor.

or Canon Ef-m 22mm F2 STM lens, focusing lens driven by screw mechanism

On the understanding of stepper motor, I first came from the middle school time to play robot experience. Robot assembly requires a wide range of actuators, the ordinary motor can be said to be "ecstasy charge", and then by other sensors to control its operating conditions (start/stop), stepper motor is more complex, need to assign value to make a definition of the form, when assembling the manipulator, The use of such a motor can not require a position sensor to obtain the existing state data, directly read the value of the variable, the impression is quite profound. I know a friend of the river, "brother", he has a mantra, "Let's talk about stepper motor Bar", this is reflected in the madness. Given the bright future of stepper motors, I am not afraid to digress, asserting that this person will become an amplifier in the future.

The organization of the focusing lens

A lens, which can be focused using the whole Mirror Group movement, can also be used to design one or several lens movements to achieve the focus; For convenience, most lenses are the latter way.

The RZ67 is an example of the overall focus of the moving lens.

Mamiya RZ67

Historically there was a unique Contax AX, which used the aforementioned point, although the manual focus lens of the Y/C port was installed, the autofocus was achieved by moving the film plane in the fuselage (relatively, moving the lens position). Of course, this kind of focus speed is not high, but it is the era of great innovation.

Contax AX, allowing manual YC-port lenses to also auto-focus

(Even now there is a voice saying that DAFA should use sensors to plug in and out of the zooming so that the old lenses of the side axle are "automated" ... Uncle has not been declared )

Aside from this wonderful flower, the arrangement of the focus lens in the Mirror group also affects the focus speed. Once there was a saying that Leica lenses are more thick glass than the Japanese resin lenses, if the auto-focus of the micro-motor to push up, "better manual." And do not say whether Leica has given up many years of dream ("background" said, Leica is the first to do things), single-Talk about the weight of the lens, it does affect the focus speed. Addiction technology has tested the FE 35mm F1.4 lens, in the other lens focus speed gap between the a7r and a7s two machine body, the lens performance is slow, the author of the small part of the tendency to think of the lens weight impact.

As an extreme example, the 200-500mm launched a monster-grade product in 2008, which requires a built-in battery, otherwise the power provided by the bayonet end is not enough to push the lens to focus.

Some manufacturers in the lens design, especially some large-scale lens focus on the focus of the light-weight lens design, such as Olympus M.zuiko 40-150mm F2.8, the focus is controlled by a combination of two light-weight lenses, driven by a VCM motor, so that the distance originally traveled by a lens is reasonably dispersed to both lenses. There's a video from a manufacturer on YouTube, or you can get a glimpse of it.

Auxiliary focusing lamp

Whether active or passive, phase or contrast, there will always be a focus on the situation, which is generally the following conditions:
1. Illumination is too low-the environment is almost light-free
2. Non-patterned solid color-such as cloudless blue sky, such as white walls
3. Low recognition vision-like the fog-shrouded lake

So the secondary focus, from these several places can be. For example, the design of the flash on the factory, because such a dim light will use the flash, or vice versa, that is, when the use of the flash is not very strong when the original light, it is natural that the manufacturers also configured on their own flash lamp auxiliary focusing lights (Assist lamp or AF illuminator).

Usually a piece of red plastic, behind the hidden led, you can play with patterns of patterns. The subject of the lack of contrast and illumination is thus able to focus precisely.

Patterns, from the United States can reach the flash
German wiki user Montauk's device

Of course, this way is not omnipotent, for the vision of the blue sky and fog, as well as the night sky, in reality or switch manual mode of focus is relatively fast. But it's good enough, isn't it?

The middle and low body often does not have the special auxiliary lamp, but also has the method, is uses the built-in flash to illuminate with the light flicker illumination, helps the AF sensor to be accurate. The high-end fuselage often comes with an auxiliary focus light, but it's different from each other. For example, Nikon and Sony (no, not black, just the first reaction to the comparison to the Basic Law), please look at the picture.

Nikon D90, a popular and long-sheng model; The red underwear right is the auxiliary light.

Nikon's D90 is probably representative, in the figure in the handle and the card mouth that reflects the white light is the auxiliary lamp. This lamp is actually an LED, light up only for lighting purposes, if taken to shoot portraits, often can not open their eyes.

Sony α700, almost the same position, the red plastic block is obscured by the auxiliary light

Sony's α700, in fact, is more like the α7 digital Sony version of Konica Minolta, the focus of the auxiliary lamp, the original flash on the same, the outward projection of red markings, even the white wall can focus. (Photo source)

This detail is easy to overlook, but subtly alters the user's flexibility of use. Only the average user will not have more than one machine comparison, and some media fast-food evaluation often will not pay attention to the differences.

This method is very inexpensive and can effectively improve the autofocus capability under certain conditions. Reminds me of a saying, "If you don't cheat, it means you haven't tried your best." However, this is not the way to apply, street and humanities photography in order not to disturb the subject, the photographer may choose to turn off the function.

Fuji S9600 Focus Assist light, green pattern

Running Coke

Running Coke is a common situation, especially when you are mixed with multi-factory card body and lens, the case in the SLR class machine more see.

This should start with the structure of the SLR.

Olympus E-3 side-profile, mirror box mystery

Or a picture from Wikimedia, a profile of Olympus E-3, which is a common construct of the last SLR. The reflector is not a single lens, but is composed of a "man"-shaped main reflector and a sub-Mirror.

The main mirror is also very different from the beginning of the SLR, the first generation of the manual focus SLR, all the light reflected in the viewfinder assembly, then the TTL mirror after the metering function, need to be divided into light, canon to represent the manufacturers put forward a fixed translucent reflector design (pellix,1965), This design, in turn, affects the movable reflector design, which is now made of translucent materials. This section can refer to "translucent mirrors".

When the SLR camera is framed, the reflector is naturally lowered, the mirror light is reflected through the reflector, upward through the focusing into the optical viewfinder assembly, the current focus screen is also more complex than the manual era, not only the type can be changed, but also through the liquid crystal on its image of the focus, you activate the focus can also be illuminated in the viewfinder prompt. So some modern SLR, when you remove the battery, then look at the viewfinder, will become dim, but also because of the non-power of the liquid crystal to reduce the transmittance caused by the light.

The light shines on the main reflector, and in addition to the viewfinder, there is a portion of the light that is transmitted to the sensor module that is emitted to the lower part of the reflector box on the sub-reflector. Don't be afraid of the complicated readers, I changed a picture from Canon's public information.

Simplified SLR composition diagram

At the time of theoretical design, the light from the mirror to the film/sensor plane should be consistent with the optical path to the autofocus sensor. This focus on the autofocus sensor also means that lifting the reflector is also a focal shot. In the actual production and assembly process, it is difficult to ensure that the two projects consistent, which caused the run-out offset.

How to solve it? This is going to say that programmability is good. Manufacturers in the factory to detect, for the offset in a certain range of circumstances, the offset is recorded, in a form of firmware written to the fuselage, in the use of different lenses in the process of the motor to promote a certain compensation operation. Individual mechanical recalibration of machines with particularly large offsets reduces the cost of mass production.

This also explains why, in some AF-designed machines, manual focus is used, and the focus is clearly seen in the viewfinder, releasing the shutter but still getting a shot of running Coke. There is another small story, the author of the university when a friend called "Anne Cannon", received a very low price problem SLR, Sony's α100. The auto-focus function of this machine is normal and reliable, only the viewfinder is blurred, and after the focusing is disassembled and reinstalled, it is intact as new. In contrast to the above structure diagram, this also shows that the framing and AF a certain degree of independence.

With day-to-day use, it may result in the displacement of the reflector, and introduce a new offset; In recent years, manufacturers in some of the high-end models, the focus on the adjustment function, users can use this to adjust their own lens compensation. Some players also through special channels, from the maintenance staff to get the manufacturer's tools, the firmware of the deviation values to modify, here is a D90 example has been invalidated.

If the use of sub-factory lens, may be read the offset compensation amount of problems, also caused by the situation is always out of focus, especially with large aperture lens, this problem is particularly obvious. Sigma has been on the pot for years-so that, for a long time, it has provided a service that the user will be able to send back to the customer service center with the body with the problem of running Coke and the appropriate horse lens, which can be corrected by the engineer. However, such services are still in trouble, such as the user's fuselage upgrades and time-consuming, and finally one day, the adaptation of the horse, "can not live like this"-the introduction of a suitable lens of the focus seat, users can connect to the computer's USB port, using the software "SIGMA optimization Pro" Adjust the lens on your own.

Connect your PC's Sigma USB DOCK with a data cable

So, in principle, a running digital SLR can focus precisely if it can be focused using a live view that lifts the reflector. The new generation of embedded phase point sensors, because AF detection is native to the sensor plane, but also theoretically eliminate the possibility of running Coke.

Branch

The rise of autofocus has become an unstoppable momentum, and there is no denying that today there are still some systems that maintain manual focus and have a unique charm, but do not affect the increasing number of discussions about autofocus.

Trap Focus

Trap Focus (TrapFocus,focus trap , or Catch-in-focus) is said to set the focus distance in the fuselage, when an object is detected to enter the focal plane, Automatically releases the shutter capture screen. Specific occasions, such as sports or wildlife, pet photography can be used. Now Pentax has a lot of machine functions, usually there are, as well as Canon machine's magic lamp firmware is also available.

Peak Focus

Peak Focus ( Focus Peak) is not a complete autofocus technology, it is the edge detection based on the sensor Live view, and on the screen or electronic viewfinder to depict the markings (Zebra) to show the contrast of objects, the user based on these tips to determine the focus and release the shutter.

In simple terms, the original contrast autofocus process is determined by the person to do the final focus. This technology is only implemented in real-time sensor viewing. This type of technology is suitable for users who transfer manual old lenses. However, in the large backlight, high Contrast environment will also have edge detection failure situation.

The peak focus feature was first delivered in 2011 by firmware upgrade on Sony's NEX machine. Since then almost all major manufacturers of non-anti-aircraft have followed suit; the E-M5 model released in early 2012, though with fast autofocus, was criticized by some users for not configuring the peak Focus feature (of course, smart users later developed a wireframe trick).

Digital split image

SplitImage Focusis an auxiliary means commonly used in the era of manual focusing, where the focusing can be implemented on the mirror system (also with the same principle but different focusing area specifications, called "micro-ridge" to focusing). The digital split image is based on the sensor's embedded phase point, and the process of the split-image focusing is realized by visualization. This feature was first provided on Fuji's x100s-type fuselage in 2013. Fujifilm UK has provided video instructions.

Face Focus

Facial priority focus is actually a pattern recognition (the patternrecognition) that focuses on the collected images through facial recognition (faceperception) under the sensor framing conditions. Some manufacturers of the machine also further, can register the face of the master and family, in the vast crowd of priority, as well as some of the functions of the group of portraits, to identify the position of the eyes on the face, the eyes of accurate coke, such as Sony, Olympus's new models, have this feature.

My e-p5, you can also choose which eye to look for OH

Eye Control Focus

Eye-controlled focusing (eye-controlled focusing, ECF) is a technology that once appeared on the Canon EOS series of film SLR. It's not really about autofocus. The essence of this is that the eye tracking device is installed in the viewfinder to detect the user's eye gaze position and to activate the focus point closest to the area in the screen.

Canon EOS 3, eye CONTROL on positive face angle

This kind of operational design is more self-conscious, but there is no dense focus on the layout of support or will not be accurate. Today's contrast focus or dual-mode hybrid focus allows for greater coverage freedom. Canon in the digital age, also did not re-carved the function, of course, who would have thought, now can simply touch the screen to choose the operation of the almost unlimited focus?

Those lenses that fail to auto-focus

This is the topic that has been discussed by friends after writing this article (little or no AF lens type). It seems that there are some truths that have not been thought of before or want to understand, and they are listed here and discussed together.

Super Macro Lens

The magnification achieved by 1:1 of the lens is called macro lens, if you can achieve greater magnification (magnification, like the ratio of objects), is generally called super macro lens. This kind of lens is used to shoot the special theme, if the ordinary macro lens may also involve ordinary still life even portrait, the most do film remake, that super macro may be used for all kinds of specimen reproduction, natural its use of the environment is relatively harsh, mostly indoor case table bright environment. In this kind of shooting, the depth of field is very shallow, often one is not enough, need to shoot several times, the late depth of field synthesis (or called focus overlay, focusstacking). In conclusion, simple autofocus seems troublesome and insignificant, and the small aperture in super macro is not enough to support phase focusing.

Examples of depth of field synthesis

However, Minolta has done 1x~3x Auto-focus ultra-macro lens, but also a wonderful industry; Canon's MP-E 65mm has a larger 1x~5x amplification capability, although there is no autofocus ability, but also the world's rare pearl level lens.

MP-E 65mm 1-5x Macro

Shift Axis Lens

The English name of the shift lens is actually the perspective control Lens, that is, the perspective controls the lens , the shift axis is only the specific operation names. This type of operation is actually very early on the larger view camera, there is a long skin can swing the moving lens to control the perspective and focus, and the exclusive lens of this kind of function developed in 135.

The shift-axis lens is the name of the lens, and it is also a past title, because now the shift-axis lens will actually have the "shift" and "Swing" (tilt) functions, and collectively tilt-shift Lenses

Canon's 17mm shift lens

The shift axis function should not affect the imaging plane and the photosensitive plane relationship, the problem should be the swing function, once swung up, the system can not accurately determine what the user wants to focus on what, and can not detect (no standard, no detection); Considering that these shots are high-pole players, the number is not many, Doesn't it seem necessary to do auto-focus?

Early 21st century, suddenly flourished tilt-shift miniature faking play, need to use the shift-axis lens reentry lens

The Turn-back lens (catadioptric Lens) is actually evolved from the telescope design used in astronomical observations, which allows the focal length of a telephoto or even super-telephoto to be achieved in a compact volume with multiple reflections of the mirror body. And because of the reason of construction, the point of light outside the Coke will also show a circle shape, by some players nickname "Donut."

These lenses tend to have a small aperture because they take care of the volume. Common F5.6, F8 and even F11, such as the amount of light, it should also be difficult to drive the phase sensor. However, the previous article actually mentioned that the United States can reach the 500mm Reflex F8 is the realization of autofocus, in addition to Minolta own Vectis system (APS System) on the 400mm F8 can also autofocus.

To turn back the lens is interested in friends can also read Mowgli Netizen "Babycashew" "I collected hundreds of reentry lens----and some not rigorous contrast."

STF out-of-focus control lens

There is an exception in the MINOLTAAF system, although it is said that the United States can achieve the super-macro and turn back into the auto-focus, but the STF 135mm lens but actually only manual focus (see article "United States can reach STF135").

Danone STF 135mm f2.5[t4.5] Lens

It's just a guess: the APD element is a center-penetrating, dark-sided construct, and the phase focus just needs the light from the side of the center, which is likely to be impossible to drive, or even driven, to work quickly.

In 2014, Fuji introduced a 56mm F1.2 lens with an APD element that could work on its own hybrid-focused x system, perhaps thanks to the help of contrast focusing? Development interview in this.

The APD element of the Fuji XF 56mm F1.2, the single-chip dyeing composition

Do not know the new era of the hybrid focus environment, will not in turn promote the above several types of lens have better performance?

other words

Autofocus is a systemic problem that involves a fairly broad range of disciplines, although this presentation looks very simple ( I tried my best ), but in practice, there are many "small problems are big problems".

There has been no autonomous lens autofocus system in China. For people to relish the domestic double bird, Phoenix and Seagull, for a long time to meet the introduction of the PK and MD compatible production lines; The masters are not skilled, but in the auto-focus swept the tide of the past glory. Such examples are also occurring in some Japanese manufacturers, not an exception.

To the digital age, there have been "patriots to create digital SLR" Rumors, a moment of chattering, and finally nothing. Instead of the digital anti-rampant 2014 and 2015, with the news, Yong Nuo made the Canon mouth autofocus lens, DJI made the MFT specifications of the AF video machine. Although it is said that scrutiny is not entirely autonomous technology, but the technology development and Exchange environment changes, also can be seen.

Auto Focus Introduction