Dual Pixel CMOS AF: five years of evolution

Tom Hurwitz, Michael Legato or Joe Simon have different experiences using Canon’s Dual Pixel CMOS AF, and their knowledge helps users to understand the advantages and disadvantages of the system.

Dual Pixel CMOS AF: five years of evolution

Introduced in 2013, Dual Pixel CMOS AF continues to evolve, as the system, which some say is the best autofocus in the market, expanded to all Canon camera segments. Five years since it first appeared, it is time to check what has changed and what the future may bring.

The recent launch of the EOS M50 represented a bit of a let down for all those who expected Canon to mix its Dual Pixel CMOS AF system with 4K in an entry level model.  Questions arose about the technical viability of using 4K and Dual Pixel AF together, but one only has to look at models as the EOS-1D X Mark II  or the EOS 5D Mark IV, which offer 4K and Dual Pixel CMOS AF, to understand that Canon is simply doing what the company has done for a long time: protecting the top models of its line.

Still, the M50 represents a new advance in terms of Dual Pixel CMOS AF, one of many that can be expected to appear for this technology that many did not believe in when it was launched, in the EOS 70D DSLR, in 2013. The EOS M50 introduced some changes to the system, offering complete vertical coverage (100%) and 88% on the wide side, in live view – with some lenses -, a gain of some 38% in terms of AF coverage, something that will be most welcome and make the system even more flexible to work with.

We can expect more developments to come, but development of Dual Pixel CMOS AF has been ongoing at Canon, even if we don’t talk much about it. Introduced in high-end models in 2016, through the EOS-1D X Mark II, which was the first full frame DSLR to feature Dual Pixel CMOS AF, the system covers, in that camera, 80% of the sensor area. Dual Pixel CMOS AF always comes associated with another feature which is important for it to work well: a touch screen LCD allowing users to select focus points, for smoother focus transition. The EOS-1D X Mark II offers that, meaning during Live View and in movie shooting, racking focus with a Canon DSLR is just a question of moving your finger over the LCD. I tried the EOS 5 DC R, from the same year, launched without DPAF, and felt that Canon really should have used the system on that model too.

Sensors with better AF and light gathering

The team behind the technology said, in a white-paper published some time ago, that Dual Pixel CMOS AF was changing the way DSLRs were used. They stated then that  “this is a shooting device that makes it possible to shoot high image quality photos and highly expressive movies on the same unit. A high dimension of expression with the new format distinguishes it from video cameras and compact digital cameras. You can capture moments with photos, or express the passage of time with movies. As a result of Live View equipped with high performance AF, we will be able to freely choose the recording method according to the objective at that time. We have accomplished another step up to a new level of DSLR cameras.”

The truth is that Dual Pixel CMOS AF made it to Canon’s Cinema EOS line of professional cameras (and even to mirrorless models), and even the original EOS C100, which did not feature DPAF, could/can be fitted with the technology at a Canon center, for a price. Canon has been playing with the options the concept of Dual Pixel sensors allows them to pursue, and not only in terms of Auto Focus. In fact, by dividing the pixels in a sensor in two, the company also managed to get better light gathering characteristics. The white paper “Advances In CMOS Image Sensors And Associated Processing”, from 2016, indicates that “among numerous design strategies in the Super 35mm CMOS image sensor developed for the EOS C300 camera was an innovative new photosite design that employed two separate photodiodes – each being 6.4 x 3.2 micrometers. For simplicity, this novel design is referred to as the Dual Pixel CMOS image sensor.”

Dual Pixel CMOS AF: five years of evolution

Choice of speeds for filming

The C300 Mark II employs a new generation Super 35mm CMOS sensor which is based on the same dual photodiode per photosite. Additional innovations within the photodiode design in combination with new on-chip noise cancellation technology have simultaneously lowered the noise floor and further elevated the saturation level of the charge well. In addition, a totally new microlens design heightens the efficiency of light direction onto the two individual photodiodes while also improving the separation between the two photodiode outputs. What this means is that the C300 Mark II offers a total of 15 stops dynamic range, another area where the exploration of dual photodiodes seems to offer better results.

Simultaneously, the C300 Mark II represents, according to Canon, a totally new Dual Pixel CMOS AF system. With the new system, Canon perfected the lens focusing, following experiences with the C100 Mark II. The EOS C300 Mark II features a menu that allows two degrees of freedom in “tuning” the response time of the lens, and the user has the choice of 10 speeds, signalling the evolution of the system within the Cinema EOS line of cameras.

The system, which initially was reserved only for the prosumer range of DSLRs and above from Canon, has now extended to different types of cameras from Canon,  from compacts and mirrorless to the Cinema EOS line, an evident suggestion that Canon is aware of the potential of the system as a marketing value. In fact, as Nino Leitner, from Cinema5D recently noted in a review of the EOS M50, “Canon has the best autofocus on the market – its Dual Pixel Autofocus – which is a big plus over all the other manufacturers. It also works brilliantly for video, when most of the competitors fall short on good autofocus for video.”

Dual Pixel CMOS AF: five years of evolution

How professionals use DPAF

Having said this, the Dual Pixel CMOS AF system is a tool, and is not perfect. There are moments when you’ve to use another technique to get your work done. That’s what one discovers when asking professionals who have used the system what’s their opinion about it. I’ve been interested in the technology since it first was revealed, and in particular in the experience of those using it, and that led to the article now published here at ProVideo Coalition.

One of the first public explanations about the usage of the system on a professional level was presented by Chuck Westfall at NAB 2014. A legend in the camera industry, Chuck Westfall, who died recently, was a photographer who served as a technical representative and advisor at Canon for decades, a professional to whom other professionals have a debt of gratitude. In this video, Chuck Westfall explains how the Dual Pixel CMOS AF upgrade for the C100 and C300 Cinema EOS cameras works.

Back in March 2014, Joe Simon recognized as one of the top wedding professional in the world, wrote one article for Canon Learning Center about his experiences with Dual Pixel CMOS AF. He wrote, then, having upgraded his C100, this: “With the release of the Dual Pixel CMOS AF upgrade, I was excited, once again, to have a new feature that would be able to pull off really amazing shots only possible with a wireless focus puller. I shoot frequently with stabilizing tools like the FreeFly MOVI M10, Glidecam HD 4000 and Kessler Stealth Dolly. With these tools, it’s hard – if not impossible – to pull focus yourself while keeping a steady shoot. But with continuous autofocus, I’m able to smoothly and naturally make focus change. Also, with the upgraded One Shot Autofocus, it’s now almost twice as fast, so it reduces the hunting and searching and, instead, locks into focus with lightning speed!”

Dual Pixel CMOS AF: five years of evolution

Tom Hurwitz on filming interviews

Recently, with the help of Catie Disabato, from Sunshine Sachs, I had a chance to ask cinematographer Tom Hurwitz, ASC, a few questions about his usage of Dual Pixel CMOS AF. The cinematographer used the system while shooting his 2018 Sundance Film Festival documentary Studio 54. When asked if he uses DPAF, Tom Hurwitz said this:

“Let me answer by linking auto-focus with live facial detection tracking, as I use them both together with my C300 Mk2. The primary situation in which I used them in shooting Studio 54, and in which I use them regularly, is in filming interviews. I often work with a small depth of field. Automatically tracking and focusing on the face of the subject is a boon to operation. With an active subject, the system is far superior to a focus puller or to me pulling focus. At 85mm with a 2.8 or lower f-stop and a super 35mm sensor, the depth of field is just a few inches. It is also very handy to use when a subject or actor is walking toward or away from camera on a very long focal length. That is also a difficult trick for the focus puller, the need for which autofocus does away with.”

DP Tom Hurwitz also mentions that “I use face detection with the focus guide feature when shooting hand-held cinema vérité style. It allows me to check my focus continually, but also lets me see focus the old fashioned way as well.”

Dual Pixel CMOS AF continues, though, to pose some problems. For Tom Hurwitz “the disadvantages come into play when the feature stops working well. Occasionally, when shooting 4K the processor is overworked and autofocus stops and starts. This bug has been improved but not totally fixed in the last firmware upgrade.” The cinematographer also adds that “I find that the focus guide stops working in some low-light or low contrast situations” and notes that “I would never use the autofocus feature when hand holding.”

Dual Pixel CMOS AF is, agrees DP Tom Hurwitz, an important feature to consider when buying a new camera, but the cinematographer expects to see Canon “improve function overall. Fix the bugs when shooting 4K. Investigate the ‘problems’ in lower light/lower contrast situations.“

Dual Pixel CMOS AF: five years of evolution

Michael Legato’s use of DPAF

Michael Legato is another cinematographer with some experience of Dual Pixel CMOS AF. Michael, who works as the right-hand-man to his father, the lauded Visual Effects Supervisor Rob Legato, uses and loves the autofocus feature on his XC15. Talking about his experience, Michael Legato says this:

“I have been using the auto focus/face tracking on the XC15 for a documentary on a Low Rider Car Crew in East LA. I have been coupling the camera with a motorized hand held gimbal to give me poor man’s steady cam.  It works incredibly well with this combination.  With this camera you are able to achieve more complex camera moves from person to person, and it has a slow rack from face to face so it feels cinematic somewhat to me.  Due to the camera’s size, it makes it especially useful to use on a hand held gimbal because I don’t have to worry about follow focus, or adding motorized gears to pull remotely.  I can keep my rig compact and lightweight while still achieving professional (enough) results. I can also record in 4k Canon Log, and have projected it in a professional screening room and feel that the results hold up while daring anyone to question whether I was using a professional camera or not.”

The cinematographer adds that “while skeptical at first, it is a great feature, that I have found, that I really love.  If this feature was available with modern Canon Cinema lenses, with a smaller body so that it could be mounted to drones, jib arms, cranes, or steady cam I could see it being incredibly useful and open a lot of doors for low budget filmmakers.  If I could use this feature on a weight balanced body with a more fluid cinematic zoom it would be the ultimate secret weapon.”

Michael Legato believes the system “gives an individual filmmaker more control with a smaller footprint” but does point to one disadvantage: “there are times where you want to control where the eye should go.  It is as simple as that,” noting, though, “that being said, it’s a tool and to know when and how to use it should be known, what its limitations are, and the feature should not be faulted for it.  I’m aware that there is a touch focus option, but I’m speaking specifically from my own experience of using it with a motorized gimbal to achieve a poor man’s steadycam.”

Despite considering it a great tool, Michael Legato says that he wishes “there was a way to more closely simulate the focus breathing similarly to a focus puller on a film in the form of a ‘cine’ focus mode, I would be thrilled. But it works as advertised now.”

New patents, new developments

Sharing these notes on the experience of different professionals using Dual Pixel CMOS AF offers readers a wider and better perspective about the system. It was important, too, to get the view from a Canon rep, and I posed Alex Sax, Pro Market Specialist at Canon USA, some questions. His answers confirm that the system has evolved, both to larger sensors than the initial APS-C from the EOS 70D DSLR, as it is now found on cameras with “a larger sensor, like the 1DX MK2, 5D MK4 and 6D MK2”. The technology has evolved and is now seen across all types of cameras available from Canon, but as Alex Sax says, “some cameras have different or more processing power which enables a more responsive experience.”

Dual Pixel CMOS AF seemed, initially, in fact, to be a a technology for medium and high-end products but now Canon is using it across different segments. I asked Alex Sax if Hybrid AF is dead and DPAF is the future, to what he replied that “the Dual Pixel AF technology works very well and customers have started using it as a precise tool for certain shots. For example, when using it on a steadicam or gimbal the face detection or object tracking AF will keep sharp focus even in a very shallow depth of field. This makes the rig lighter and allows the operator to achieve more dynamic shots without the need for expensive accessories. This means an entry level camera has some of the same features as a pro level camera and it allows more options for filmmakers.” I guess, from his reply, that Hybrid AF is not going to be used again.

As a final question, to which I – and I believe we all – somehow, know the answer, I asked  Alex Sax if the system is going to evolve further. He replied this: “we cannot comment on future products, but we are seeing a lot of filmmakers use the DPAF for specific situations, not a total replacement but rather a convenient feature used only when necessary. It is a very reliable tool and has a lot of practical applications in modern production settings.”

Dual Pixel CMOS AF: five years of evolution

Canon continues to explore new ways to expand the system, there is no doubt about it. The new options available in the EOS M50 are a clear indication of the continued development of Dual Pixel CMOS AF. Furthermore, new patent applications published at the United States Patent and Trademark Office in February and March suggest that Canon continues to explore ways to split its pixels in new ways, to better gather light and also to expand the options in terms of AF control.  So, yes, Dual Pixel CMOS AF sensors are evolving…

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Journalist, writer and photographer since 1979, both print and online, with a vast experience in the fields of photography, software, hardware, web, aviation, History, video games, technology, having published content in almost all Portuguese newspapers…