1 просмотров
Рейтинг статьи
1 звезда2 звезды3 звезды4 звезды5 звезд
Загрузка...

Laser Autofocus, PDAF, CDAF, Dual Pixel AF Explained: Which is better?

Содержание

Навестись за мгновение: фазовый автофокус в работе

Всем продвинутым пользователям известно, что качество снимков определяется не количеством мегапикселей, а размером матрицы, светосилой, объективом и другими характеристиками. Одним из важных параметров современной мобильной камеры стал автофокус — от его работы зависит, будет ли объект съёмки чётким даже при быстром движении. Сейчас существует несколько разновидностей автофокусировки, но самым последним тенденциям соответствует фазовая. О преимуществах фазового автофокуса мы и поговорим в сегодняшней статье, вооружившись Honor View 10.

Зачем нужен автофокус?

Начнём с того, что сегодня практически в любом смартфоне, даже самом бюджетном, есть система автофокусировки. Грубо говоря, автофокус — это когда камера гаджета самостоятельно наводит резкость во время съёмки фото и видео. Он нужен для того, чтобы максимально упростить процесс и не крутить каждый раз настройки, как при съёмке на профессиональный зеркальный фотоаппарат.

Работу автофокусировки вы в большинстве случаев просто не заметите: резкость настраивается автоматически, как только вы включаете камеру или нажимаете на кнопку затвора. Если нужно сделать фокус на каком-то определённом объекте, как правило, достаточно лишь тапнуть по нему на экране устройства.

Актуальные типы автофокусировки

На сегодняшний день существует три основных вида автофокусировки.

Контрастный автофокус. Относится к пассивному типу, то есть сенсоры камеры ничего не излучают. В основном данное решение применяется в недорогих смартфонах. Главная причина в том, что такой вид фокусировки — самый простой. Камера ориентируется на величину светового потока, попадающего на матрицу. Перемещая линзу, программное обеспечение добивается наибольшего контраста и таким образом фокусируется на объекте съёмки. Именно поэтому бюджетным гаджетам на фокусировку требуется несколько секунд, за которые легко упустить или смазать движущийся объект.

Лазерный автофокус. Достаточно свежая технология, относящаяся к активному типу фокусировки. В основе лежит принцип лазерного дальномера: лазер освещает объект, а сенсор измеряет расстояние до него, основываясь на времени поступления отражённого лазерного луча.

Один из главных плюсов лазерного фокуса — время. Весь процесс занимает доли секунды, что позволяет мгновенно делать резкие снимки. Причём лазерный фокус не теряет в скорости ни в тёмное время суток, ни в непогоду. Но у данной системы есть серьёзный недостаток. Дальность работы лазера в камере едва переваливает за пару метров. На всё, что располагается дальше, гаджет наводится при помощи других типов фокусировки.

Фазовый автофокус (PDAF). Также относится к активному типу. Его устанавливают во многие смартфоны, включая Honor View 10. При фазовой автофокусировке лучи из разных точек объектива сводятся на встроенные в матрицу датчики. Если объект находится в фокусе, то световые потоки от него сходятся в одну точку на датчике. Если же нет, то программное обеспечение, основываясь на расстоянии между лучами, сдвигает линзы на нужную величину.

Данная система хороша в первую очередь высокой скоростью работы: можно фокусироваться на быстро движущихся объектах. Например, Honor View 10 требуется менее 0,3 секунды, чтобы сфокусироваться.

Единственный недостаток — ночная съёмка. В диафрагму смартфона поступает недостаточно света, из-за чего автофокусировка может занимать чуть больше времени. Кроме того, у фазового автофокуса довольно сложная реализация. Система призм, зеркал, линз требует сверхточной установки и не менее скрупулезной программной настройки.

Пример работы фазового автофокуса

Как уже было сказано выше, принято считать, что фазовый автофокус в тёмное время суток хуже справляется со своей задачей. Однако современные гаджеты оснащаются высокочувствительными сенсорами и продвинутыми алгоритмами, которые помогают камере правильно сфокусироваться даже при недостатке освещения.

Мы протестировали работу камеры Honor View 10 ночью. В устройстве имеется система «искусственного интеллекта»: она дополнительно анализирует картинку с камеры и настраивает параметры съёмки и фокусировки таким образом, чтобы получить максимально резкий и качественный кадр.

С фокусировкой как в дневное, так и в ночное время на Honor View 10 никаких проблем нет. Она работает быстро и точно, ловя объект за доли секунды.

Вдобавок для съёмки динамичных сюжетов у камеры View 10 есть опция «Автофокус в движении».

Если она заранее активирована в меню, то после тапа по объекту автоматика начинает отслеживать его перемещения, фокусируясь на нём постоянно.

Это удобно при съёмке детей или животных — тех, кто двигается быстро, а порой и вовсе молниеносно. Благодаря данной функции можно поймать интересный момент, который бы пропустил или смазал другой смартфон. Например, две собаки, носящиеся по двору, получаются такими же чёткими и резкими, как если бы они неподвижно стояли на месте.

Итоги

В данный момент самая актуальная технология фокусировки в смартфонах — фазовая. Она быстро и точно работает, а при недостатке освещения ей помогают программные ухищрения — такие, как специализированные интеллектуальные алгоритмы в Honor View 10, позволяющие автофокусу работать ещё более успешно в любых условиях.

Dual Pixel Autofocus: What is it and what cameras have it?

Canon introduced phase detection dual pixel auto focus (DPAF) in 2013, with the EOS 70D camera, calling the technology “revolutionary.”

Since then, DPAF has been a feature on most new camera models released by Canon, from the $10,000 EOS C300 cinema camera, to the pro-level EOS 1DX MarkII, to Canon’s mirrorless EOS M6, to the consumer EOS Rebel T7i.

DPAF is also showing up in smart phone cameras by Samsung and others, and several of the big camera companies have filed patents for similar types of sensors.

But what is dual pixel auto focus?

Is it really revolutionary?

Does any other manufacturer offer a similar technology?

What is Dual Pixel Auto Focus?

On these new Canon CMOS imaging sensors, each pixel has two photo diodes which can operate separately or together. Each diode has a separate lens over it.

When light goes through those lenses and hits the diodes, the processor analyzes each diode’s signal for focus and, once focus is achieved, the signals are then combined to record the image.

Each pixel on the sensor, then, has a dual role.

That dual role is what makes DPAF sensors different.

In other kinds of imaging sensors, some of the pixels are used for focus and the rest record the image, but none does both.

In Canon imaging sensors, 80% of the pixels (horizontally and vertically) play that dual role.

The sensor on the EOS 5D Mark IV, for instance, is 6720 x 4480 pixels. At 80% coverage (5376 x 3584) more than 19 million pixels have DPAF.

By comparison, the Sony a7R iii sensor is 7952 x 5304 pixels and has 399 phase detection auto focus points.

While mirrorless cameras have been using phase detection auto focus in imaging sensors for some time, DSLRs typically use a separate phase detection auto focus sensor for focusing while the mirror is down and the viewfinder in use, and switch to contrast detection auto focus on the actual imaging sensor when the mirror is up and you’re using Live View or recording a video.

And video is where DPAF can really shine, providing quick and accurate focus without the lens zooming in and out seeking focus.

DPAF also makes following and keeping focus on moving subjects much easier and more accurate.

And, you can easily manage focus and switch between subjects while shooting video using the touch screen in live view.

For still photography, you can tap anywhere on the LCD screen on the back of the camera and get quick, accurate focus.

Dual Pixel Auto Focus: each pixel contains two photodiodes that operate independently. Screen grab from a Canon video.

Which Cameras Have DPAF?

The following Canon cameras have DPAF:

  • C100, C200, and C300 cinema cameras
  • M5, M6, and M50 mirrorless cameras
  • 1 DX Mark II, 5D Mark IV, 6D Mark II, 7D markII, 70D, 77D, 80D, Rebel T71 (also known as the EOS 800D) and the Rebel SL2 (EOS 200D) DSLRs

The cameras in several smart phones also boast DPAF:

  • Samsung introduced DPAF in the Galaxy S7 and S7 Edge smart phones. DPAF sensors are also in the S8, S8+, S9 and S9+.
  • Google’s Pixel 2 smart phones have DPAF sensors.
  • The HTC U11 phone also has a DPAF sensor.

A number of websites that follow the market report that Fuji, Nikon, Olympus, and Panasonic have filed patents for dual pixel autofocus (or very similar) systems.

Is DPAF Really a Game Changer?

Before making a judgement about dual pixel auto focus, you have to understand how autofocus works and what DPAF does differently.

In a DSLR, there are two sensors: a focusing sensor and an imaging sensor.

When you’re using the viewfinder to compose your image, the mirror is down.

That mirror reflects an image of the scene you’re about to shoot up into a pentaprism and into the viewfinder.

A small translucent bit in the mirror also allows an image of the scene to be reflected down to the autofocus sensor (which is different from the imaging sensor that will capture the photo).

Читать еще:  Вирус на Андроид. Как найти и удалить опасное приложение

If, on the other hand, you are composing using Live View, then the mirror is up, the focusing is done via the imaging sensor and the autofocus sensor is not used.

Typically, the focusing sensor uses phase detection and the imaging sensor uses contrast detection to auto focus.

Contrast detection looks at the micro contrast along edges.

It can tell if the edge is sharp or not in focus, but it can’t tell if the lens is front focusing or back focusing.

So, it instructs the lens to move forward and backwards to determine which way and how far to move to acquire focus.

This process is slow, compared to phase detection auto focus. However, because it uses the actual sensor, you can be sure of getting accurate focus.

How phase detection auto focus works. Screen grab from Canon video.

Phase detection auto focus works kind of like old range finder cameras, where you’d see two images and adjust focus until you bring them together as one.

With phase detection, the focusing sensor takes the signal from two diodes that are slightly separated and compares each.

If the signal matches, and the light from each hits the same place, then focus is achieved.

If the signals are apart and the light doesn’t line up, a phase detection system measures how far apart and in which direction and then smoothly moves the lens forward or backward to the point where focus is achieved.

(I should note that the phase detection sensor in a DSLR can be slightly misaligned during the manufacturing process, which could lead to images that are slightly out of focus. That would be annoying but can be fixed.)

Phase detection is noticeably faster than contrast detection auto focus, which is helpful when shooting sports, wildlife, weddings, etc.

It matters less for still objects like landscapes.

It matters more when shooting video, where you want focus to happen quickly and seamlessly.

A DSLRs focusing sensor will have certain number of phase detection points for autofocus.

The EOS 5D Mark IV has 61 auto focus points, for example. My Nikon D750 has 51.

However, if I’m using Live View (with contrast detection on the imaging sensor), I’m not restricted to 51 points—I can place my focus anywhere on the Live View screen.

Mirrorless cameras, by contrast, just have the one sensor that typically uses phase detection auto focus. Sony’s a7R iii has 399 focus points.

The Olympus OM-D EM-1 MK II has 121 focus points.

Each of these focus points represents a pixel that’s not recording image data.

It is just being used for focus and the image data is interpolated from nearby pixels.

While that can have a minor effect on image quality, it’s not enough to notice.

What you get in focus speed and accuracy more than make up for any miniscule loss of image quality.

Is DPAF Really Revolutionary?

Dual Pixel Auto Focus is certainly an interesting technology.

With every pixel on the sensor capable of recording your image, the image quality could be marginally better but, with today’s sensors, you will probably never be able to tell the difference.

For a landscape photographer, it’s not a compelling reason to get a new camera, though it might be nice to have.

If you’re doing portraits or photographing events and weddings, you’ll probably be composing and focusing through the viewfinder and won’t really use DPAF.

For videographers, though, this could be big!

Most professional videographers have used manual focus to avoid having the lens hunt for focus.

In Hollywood, for each scene the camera-to-subject distance is measured out and focus noted for anywhere the actors will be.

As the scene unfolds, the camera operator manually moves the lens to those predetermined focus points.

Videographers using a DSLR to record video often made sure the focus was right before recording each shot.

By contrast, dual pixel auto focus can give you immediate, accurate focus without the lens hunting back and forth.

You can tap the LCD screen and quickly and easily set the focus on a different subject.

With phase detection DPAF, the camera will respond smoothly and almost instantaneously.

The camera will be far less likely to lose focus when a person or object crosses between you and your subject or when there’s a bright light or a high contrast area in the scene.

Canon also claims that the DPAF system is much faster and better at keeping moving objects in focus.

People who are currently using mirrorless cameras for stills or videos probably won’t find DPAF a compelling reason for buying a new camera or system.

Many of the mirrorless brands shoot video in 4K, but not all Canon DSLRs do. And Sony’s a7Riii’s 399 focus points seem plenty.

In smart phone cameras, DPAF will have the same kinds of benefits as in DSLRs, particularly with video.

In addition, DPAF can help simulate the bokeh you often can’t get with smart phone cameras.

(Smart phone cameras’ depth of field is enormous due to their small image sensors and proximity to the lens.)

Apple and other manufacturers have used dual cameras to achieve the same effects.

As more people start using phones to record videos and as phones get more sophisticated and capable, this could be a good selling point.

DPAF is coming!

Dual Pixel Auto Focus provides enough of a benefit that most of the camera companies and phone makers are working on it.

Patents have been filed and rumors abound about which cameras will get it and when.

You’ll probably get it the next time you upgrade your gear.

Would I sell everything to get a DPAF camera now?

No.

It’s a “nice to have,” not a “must have.” However, if I was doing a lot of video, I might be really tempted.

Will it be in every camera in the next few years? Yes. And it that will be a good thing.

Laser Autofocus, PDAF, CDAF, Dual Pixel AF Explained: Which is better?

We all know what does we mean by saying a focused picture. Well, if you don’t know, look at the below image. Clearly the picture on the right looks more pleasant and clear to our eyes while the other picture seems blurred.

There are two ways we can adjust the focus. 1. The manual focus adjustment. 2. Autofocusing systems.

In manual mode, focal length of the lens is adjusted manually by hand so as to get a clear picture. In autofocusing systems, we rely upon electronic-mechanical systems to adjust the lens focal length. If you have ever used a magnifying glass to get the focused image, you will get this concept easily. To get a clear image, you will have to adjust the lens up and down. Indirectly you are doing the autofocus. It is your brain (eyes are the sensors and controller the brain) telling you to adjust the glass.

Most common autofocusing systems are:

  1. Phase detection auto focus (PDAF)
  2. Contrast detection auto focus (CDAF)
  3. Laser auto focus (LAF)
  4. Hybrid auto focus (HAF)

Among these, PDAF and CDAF are the most popular autofocusing methods.

Contrast detection autofocus

This system relies on the contrast of the image which it is received. Sensor detects the contrast of the image in first lens position, and moves the lens forward or backward to get the contrast of the image in the new position. Then it compares the first result and second result and hunts for next possible best position of the lens. You might notice some sounds coming from the camera while it performs these, even from smartphone cameras which employs this.

Pros of CDAF

  • Simple technology
  • Good enough for static pictures

Cons of CDAF

  • It takes some time for the system to find the best position for the lens, probably even few seconds
  • It fails on a moving object, results in poor focusing
  • Not an ideal solution for videos

Due to the disadvantages of contrast detection AF, PDAF is introduced

Phase detection autofocus

This type of autofocus is usual in today’s smartphones. PDAF relies on image processing more than mechanical adjustments to get the correct focus. It splits the image into 2. Then the system internally tries to move the image and align the lens accordingly. When it is aligned we get a focused image.

Pros of PDAF

  • Mechanical elements are not involved in focusing, making it faster than CDAF.
  • It is good at focusing moving images and videos

Cons of PDAF

  • Certain percentage of the pixels in sensor will be allocated to focusing.

Today’s smartphones and and DSLR’s are using dual-pixel auto focusing systems. Example : Samsung Galaxy S7

Dual Pixel autofocus

With PDAF, only 5 % of the available pixels were part of focusing. But in Dual pixel focusing, a phase detection photo diode is embedded into each and every pixel on the camera sensor.

Dual pixel focusing systems are superior than PDAF and hybrid systems.

Laser autofocus

This system employs a small laser transmitter and a receiver. It sends a laser beam to the subject and it bounces back to reach the receiver. Using some mathematical algorithms, It calculates the time taken for the beam to hit the subject and come back.

Pros of Laser autofocus

  • It is the fastest autofocusing
  • Works in very low lighting

Cons of Laser autofocus

  • Fails to focus subjects on the long distance as the laser transmitter is not a powerful one.

Hybrid autofocus

Some cameras employ multiple focusing systems to minimize the disadvantages of both the systems. For example, many of the SONY sensors are using both PD & CD together. Another example would be Google Pixel, which uses PDAF and Laser autofocus.

Навестись за мгновение: фазовый автофокус в работе

Всем продвинутым пользователям известно, что качество снимков определяется не количеством мегапикселей, а размером матрицы, светосилой, объективом и другими характеристиками. Одним из важных параметров современной мобильной камеры стал автофокус — от его работы зависит, будет ли объект съёмки чётким даже при быстром движении. Сейчас существует несколько разновидностей автофокусировки, но самым последним тенденциям соответствует фазовая. О преимуществах фазового автофокуса мы и поговорим в сегодняшней статье, вооружившись Honor View 10.

Читать еще:  50 языков — 50 languages

Зачем нужен автофокус?

Начнём с того, что сегодня практически в любом смартфоне, даже самом бюджетном, есть система автофокусировки. Грубо говоря, автофокус — это когда камера гаджета самостоятельно наводит резкость во время съёмки фото и видео. Он нужен для того, чтобы максимально упростить процесс и не крутить каждый раз настройки, как при съёмке на профессиональный зеркальный фотоаппарат.

Работу автофокусировки вы в большинстве случаев просто не заметите: резкость настраивается автоматически, как только вы включаете камеру или нажимаете на кнопку затвора. Если нужно сделать фокус на каком-то определённом объекте, как правило, достаточно лишь тапнуть по нему на экране устройства.

Актуальные типы автофокусировки

На сегодняшний день существует три основных вида автофокусировки.

Контрастный автофокус. Относится к пассивному типу, то есть сенсоры камеры ничего не излучают. В основном данное решение применяется в недорогих смартфонах. Главная причина в том, что такой вид фокусировки — самый простой. Камера ориентируется на величину светового потока, попадающего на матрицу. Перемещая линзу, программное обеспечение добивается наибольшего контраста и таким образом фокусируется на объекте съёмки. Именно поэтому бюджетным гаджетам на фокусировку требуется несколько секунд, за которые легко упустить или смазать движущийся объект.

Лазерный автофокус. Достаточно свежая технология, относящаяся к активному типу фокусировки. В основе лежит принцип лазерного дальномера: лазер освещает объект, а сенсор измеряет расстояние до него, основываясь на времени поступления отражённого лазерного луча.

Один из главных плюсов лазерного фокуса — время. Весь процесс занимает доли секунды, что позволяет мгновенно делать резкие снимки. Причём лазерный фокус не теряет в скорости ни в тёмное время суток, ни в непогоду. Но у данной системы есть серьёзный недостаток. Дальность работы лазера в камере едва переваливает за пару метров. На всё, что располагается дальше, гаджет наводится при помощи других типов фокусировки.

Фазовый автофокус (PDAF). Также относится к активному типу. Его устанавливают во многие смартфоны, включая Honor View 10. При фазовой автофокусировке лучи из разных точек объектива сводятся на встроенные в матрицу датчики. Если объект находится в фокусе, то световые потоки от него сходятся в одну точку на датчике. Если же нет, то программное обеспечение, основываясь на расстоянии между лучами, сдвигает линзы на нужную величину.

Данная система хороша в первую очередь высокой скоростью работы: можно фокусироваться на быстро движущихся объектах. Например, Honor View 10 требуется менее 0,3 секунды, чтобы сфокусироваться.

Единственный недостаток — ночная съёмка. В диафрагму смартфона поступает недостаточно света, из-за чего автофокусировка может занимать чуть больше времени. Кроме того, у фазового автофокуса довольно сложная реализация. Система призм, зеркал, линз требует сверхточной установки и не менее скрупулезной программной настройки.

Пример работы фазового автофокуса

Как уже было сказано выше, принято считать, что фазовый автофокус в тёмное время суток хуже справляется со своей задачей. Однако современные гаджеты оснащаются высокочувствительными сенсорами и продвинутыми алгоритмами, которые помогают камере правильно сфокусироваться даже при недостатке освещения.

Мы протестировали работу камеры Honor View 10 ночью. В устройстве имеется система «искусственного интеллекта»: она дополнительно анализирует картинку с камеры и настраивает параметры съёмки и фокусировки таким образом, чтобы получить максимально резкий и качественный кадр.

С фокусировкой как в дневное, так и в ночное время на Honor View 10 никаких проблем нет. Она работает быстро и точно, ловя объект за доли секунды.

Вдобавок для съёмки динамичных сюжетов у камеры View 10 есть опция «Автофокус в движении».

Если она заранее активирована в меню, то после тапа по объекту автоматика начинает отслеживать его перемещения, фокусируясь на нём постоянно.

Это удобно при съёмке детей или животных — тех, кто двигается быстро, а порой и вовсе молниеносно. Благодаря данной функции можно поймать интересный момент, который бы пропустил или смазал другой смартфон. Например, две собаки, носящиеся по двору, получаются такими же чёткими и резкими, как если бы они неподвижно стояли на месте.

Итоги

В данный момент самая актуальная технология фокусировки в смартфонах — фазовая. Она быстро и точно работает, а при недостатке освещения ей помогают программные ухищрения — такие, как специализированные интеллектуальные алгоритмы в Honor View 10, позволяющие автофокусу работать ещё более успешно в любых условиях.

Camera Tech Explained: Canon Dual Pixel Autofocus

Often knocked for a perceived lack of innovation, Canon does have at least one ace up its sleeve over the competition – dual pixel autofocus.

Introduced with the 70D in 2013, dual pixel autofocus significantly increases autofocus speed and accuracy in Live View mode, including autofocus while shooting DSLR video. Recent Canon DSLR cameras are lauded as having sweet autofocus racking and tracking capabilities for video, and dual pixel autofocus is the reason.

While Canon has only recently become a competitor in the mirrorless marketplace with the introduction of the M5 in 2016, its current DSLR lineup can offer a competitive live view experience thanks to dual pixel autofocus, and with the rising popularity of DSLR videography, the video mode autofocus is a real selling point. From my experience, it performs quite well. In conjunction with tap-to-focus touchscreen capabilities, it offers impressively smooth and accurate focus racking without fumbling around to grab exact focus manually.

But, what is dual pixel autofocus, exactly? Canon has recently updated their online learning library with some new content to break it all down, for those technical-minded people who love to dig into the inner workings of camera technology.

[REWIND:] SHOOT FILM STYLES ON YOUR CANON, IN-CAMERA, WITH A BIT OF WORK | CANON PICTURE STYLES

Excerpted from Canon’s knowledge base:

“Put simply, DPAF takes autofocus to the next level. It provides both smooth and consistent focus for a wide range of photo and video applications. Each pixel on the CMOS imaging sensor has two separate, light-sensitive photodiodes, which convert light into an electronic signal. Independently, each half of a pixel detects light through separate micro lenses, atop each pixel.

During AF detection, the two halves of each pixel — the two photodiodes — send separate signals, which are analyzed for focus information. Then, an instant later when an actual image or video frame is recorded, the two separate signals from each pixel are combined into one single one, for image capturing purposes. This greatly improves AF speed over the majority of the area on which you’re focusing. The result is phase-detection autofocus, which surveys the scene and recognizes not only whether a subject is in focus or not, but in which direction (near or far), and by how much.”

Check out this video to see it in action, and you can read more in Canon’s article, from which the excerpt was taken, here.

For vloggers and DSLR videographers, Canon’s dual pixel autofocus technology offers a real reason to opt for this brand, and to stick with a DSLR, in an era in which consumer camera technology is leaning more and more toward mirrorless.

Phase Detection AF Concept

The first important thing to keep in mind is that this utilizes the phase-detection concept of focus detection. This means comparing multiple rays of light, and being able to immediately determine not just sharpness or lack of sharpness, but two vital things:

• Which direction the lens needs to be driven, to get sharp focus

• How far it will need to be driven

Many AF systems in earlier cameras — and in many competitive “mirrorless” cameras, as of April 2018 — either combine this concept with a support method called Contrast AF, or rely on contrast-based focus detection entirely.

Contrast detection usually can’t initially establish the direction to drive the lens for sharp focus, nor can it predictably halt the lens’ focus drive at the instant sharp focus is reached. Instead, it reads sharpness of an area of the imaging sensor, and looks for when the greatest contrast among adjacent pixels on the image sensor occurs.

And, to get there, contrast detect AF usually has to rock the lens back and forth, past the point of sharpest focus, then reverse the lens and move its focus again. This can sometimes happen multiple times.

The Canon Dual Pixel CMOS AF method is 100% phase-detection, so the two primary benefits are always there when using autofocus with EOS DSLRs and mirrorless models with this technology at the imaging sensor.

AF that covers the entire image sensor — not a limited number of “AF points”

Dual Pixel CMOS AF, as of April 2018, is the only industry AF technology that uses every pixel on the imaging sensor to detect focus, and also to capture actual image information for still and video imagery. Focus can be detected anywhere, within a “live” area covering about 80% of the horizontal and vertical width of the entire CMOS imaging sensor.

We’ll discuss in a moment how each pixel’s information is divided in two. But the important thing to initially understand about Canon’s Dual Pixel CMOS AF is that unlike competitive systems (as of April 2018), each and every pixel on the image sensor can be used for focus detection. In this conceptual illustration from Canon’s engineers, each “block” represents one pixel, and the blue and red halves of each represent the dual light-sensitive areas in each pixel, which are used for focus detection.

This is important, and a reason for DPAF’s smoothness when focusing upon many subjects. Unlike many other systems using phase-detection to focus off the imaging sensor, DPAF does not use scattered pixels on the image sensor, nor does it use pixels exclusively for AF (and requiring the use image information from neighboring pixels to fill-in the missing image detail from those locations used for focus detection).

Читать еще:  Командующие армией России начали получать специальные телефоны

This conceptual illustration depicts one method of using scattered, individual pixels on an image sensor for phase-detect AF. Frequently, these pixels record brightness for focus detection only, and are “re-mapped” in processing to provide data for actual image recording. Information from pairs of pixels is compared to determine focus, which are illustrated here in green and blue. One problem with this approach is it often is not able to gather sufficient information for true focus control in a variety of situations, so contrast detection is added as a backup for AF — and remember, contrast detection often has issues with being forced to “hunt” back and forth, and so on. Again, this is a conceptual illustration only, and not a literal depiction of competitive phase-detect sensor layouts.

Accordingly, you won’t hear claims of focus from “xx number of AF points” with Dual Pixel CMOS AF. It’s not restricted to limited numbers of locations on the image sensor, where dedicated pixels for AF replace ordinary light-gathering pixels, for focus detection exclusively. Information from each and every pixel is available, before image recording of a still image or video frame, to contribute to determining sharpness at the area of a subject you’ve asked it to focus upon.

Dual Pixel CMOS: each pixel has TWO light-sensitive areas

The area of each pixel on a digital camera’s image sensor that records brightness is called a photodiode. This tiny area acts like a miniature light meter, and when an image is recorded, it generates an electronic signal in proportion to how much brightness it received. The greater the brightness at a given pixel, the greater the strength of the signal it generates.

Sophisticated processing from each pixel is used to assemble these millions of individual electronic signals into recognizable frames of video, or still images.

Dual Pixel CMOS AF takes this concept and expands upon it. Every pixel on the CMOS imaging sensor has its light-sensitive photodiode split in two. There’s a distinct left and right half, which for our purposes we can label the A and B parts of each pixel. Each can detect light, and during focus detection (before each video frame is recorded, or before a still image is actually recorded), it delivers two separate signals — independent ones for the A-side and B-side.

During focus, the two light-sensitive areas of each pixel operate independently. Each receives light from the camera’s lens, and sends its own electronic signals to a processor. These are gathered, and compared (A vs. B). From deviations between the two, Dual Pixel CMOS AF is able to detect whether the area being sampled is already in sharp focus, or whether we need to move the lens to a closer or more distant focus position to get the sharpness we need.

Here’s a conceptual illustration, showing how during focus, the “B” side of a pixel gathers light and delivers its own independent information to the processing system. When separate information from the A and B sides of groups of pixels is gathered, it can be analyzed and accurately provides sharp focus, during Live View and video recording.

The genius of Canon’s Dual Pixel CMOS AF is that when groups of pixels are assessed, the differences in read-outs from the A-side and B-side can detect focus. And in true phase-detect fashion, they don’t only see “sharpness,” but can instantly detect which direction the lens must move for sharp focus, and by how much. Again, this is done so effectively that there is no need for contrast-detection technology as a backup to ensure good, sharp focus.

The split, light-sensitive areas of a pixel produce combined output an instant after focus detection, when actual gathering of light for image-recording is done. This is why, for example, the 24.2 million pixel CMOS sensor on a camera like an EOS Rebel T7i still records 24.2 million pixels of image data, even though each pixel is split in half for focus detection purposes.

Smooth, continuous Servo AF, for moving subjects

Dual Pixel CMOS AF would be a cool innovation if it could only focus upon stationary subjects. But a wonderful addition on recent EOS models, like the EOS 5D Mark IV, EOS 80D, EOS 77D, and Rebel T7i cameras is its performance when continuously focusing, especially with moving subjects.

Unlike many competitive systems, that have to update focus for moving subjects in successive lens movements — and you can see this, as a moving subject and its background both seem to visually “twitch” in and out of focus — Dual Pixel CMOS AF is able to provide smooth and continuous transitions, to follow moving subjects.

All you have to do is set the camera’s AF Operation from One Shot to “Servo.” With video or Live View active, with most recent EOS models having touchscreen operation, simply press the Q-button or Q-icon on the LCD monitor to call up the Quick Control Menu. Tap the AF Operation icon, and choose SERVO. (Models with DPAF, but without touchscreen — like the EOS 7D Mark II — require going into the red shooting menu, and setting MOVIE SERVO AF for continuous focus during video recording.)

This steady performance during continuous focusing is especially true with Canon lenses that are optimized for smoothest Live View and video AF:

• Canon lenses with STM (Stepping Motor) focus technology

• Canon lenses with Nano USM focus motor technology

Whether you’re using an EF, EF-S, or EF-M lens, if you see either of these technologies identified on the exterior of the lens, you know you’ll get the ultimate in smooth, positive AF performance when combined with Canon EOS cameras offering Dual Pixel CMOS AF.

AF that’s optimized for the different needs of still and video

Another brilliant aspect of Canon’s Dual Pixel CMOS AF technology is that its developers realized from Day One that to work effectively, it would have to provide the AF that video users need. Not just simply “getting things in focus,” but getting it done the way a pro video camera operator would want to.

When we shoot still images, we normally want the fastest focus response possible. We press the button on the camera, and we want and expect that the image will jump into focus, without hunting back and forth, and without indecision from the AF system.

But video is different. If the sharp focus during a live video recording just instantly jumps from one distance to another, it’s normally a very jarring visual experience for viewers. Think about it: this is rarely done, unless for a very special, sudden visual impact, in movies or most TV shows. Instead, professional-recorded video normally smoothly transitions, or “racks,” from one distance to another. There’s usually a smooth and much slower progression as focus changes from a foreground to background, or vice-versa.

Canon’s Dual Pixel CMOS AF does the same thing, when Movie Servo AF (sometimes labeled “Servo AF”) is active. Focus is deliberately slowed down, so that changes have a professional, smooth look to them.

And, on advanced EOS models (like the EOS 80D and 5D Mark IV), you have additional menu controls:

Adjust the rate of changes as you rack focus from near to far, or vice-versa…slow it down from the factory-default response in up to seven steps, or speed it up in two steps. It’s done on a scale on the AF Speed menu, in the red shooting menu area. Camera must be set for video recording to display this menu setting.

Movie Servo AF tracking sensitivity:

How quickly will the Dual Pixel CMOS AF respond, if you’re focusing on one moving subject, and then something comes between you and that subject? Will it instantly try to re-focus on the new subject, or allow time to find that original subject again?

These cameras have adjustments for Dual Pixel CMOS AF, when Movie Servo AF is active, to either make the system respond even faster and re-focus on new subjects (“responsive”), or instead to resist changes in focus if there’s a sudden change in what the active AF area sees (“Locked-on”). You can adjust up to three steps, in either direction, to fine-tune the camera’s response.

Summary

Especially when you combine the great responsiveness and control of the touchscreen interface on cameras like the Canon EOS Rebel T7i, EOS 77D, or EOS 80D, with the steady and positive action of Dual Pixel CMOS autofocus, it’s a truly winning combination — for Live View when you shoot still images, and of course for video shooting as well.

Dual Pixel CMOS technology is a tremendous engineering accomplishment, when you consider that it uses dual read-outs of data from each pixel on the image sensor, and processes those millions of pieces of information into smooth focus action. There are definite benefits to Canon’s traditional phase-detection AF when you focus through the eye-level viewfinder, but Dual Pixel CMOS AF adds a new dimension to what technology can bring to photographers when they want or need to focus using the LCD monitor instead. If you haven’t yet experienced Canon’s Dual Pixel CMOS, you owe it to yourself to see it in action at your Canon dealer.

Canon Cameras with Dual Pixel CMOS AF

This list is constantly growing, as new cameras are developed and introduced. The first EOS camera with Dual Pixel CMOS AF was the EOS 70D, introduced in 2013. As of April 2018, the following Canon EOS models use Dual Pixel CMOS AF technology:

EOS M-series “mirrorless” models:

EOS digital SLRs with APS-C size sensors:

EOS digital SLRs with full-frame sensors:

EOS-1D X Mark II

* Servo AF (continuous focus on moving subjects) possible during Live View still-image shooting

Ссылка на основную публикацию
Статьи c упоминанием слов:
Adblock
detector