December 01, 2015
By: Loren Simons
When Dual Pixel CMOS Autofocus (AF) was first introduced in the Cinema EOS Product line with the EOS C100, it made a big splash in the independent film world. Until that point, autofocus in large sensor cameras brought flashbacks of lenses endlessly searching for any bit of contrast to grab onto and hold. But the EOS C100 changed all that. Now, filmmakers had an autofocus mechanism that was smooth, organic, and accurate. It made slider moves painless, walk and talks a joy, and gimbal operators rejoice. It truly was an innovative technology. The EOS C300 Mark II builds on that same technology, stripping away some of the first generation limitations and drastically expanding the capabilities of the technology. We are going to talk about some of those innovations shortly, but first, some tech-talk.
Dual Pixel CMOS AF isn’t your father’s autofocus. While traditional AF like the one found in most cameras on the market is based off contrast, Dual Pixel CMOS AF is based off a technology called “phase-detection.” Essentially, the AF of olden days would look for contrast between lines in your image: a hard edge between a billboard and the sky or the line of a nose against a face; while the phase-difference in Dual Pixel CMOS AF works in an entirely different way. Just take a look at the name itself, Dual Pixel, and you’ll get a hint about how this works. As you can see in the image below, Dual Pixel CMOS AF is actually a sensor-based technology. It requires that behind each pixel on the sensor, there are two separate photodiodes. Each photodiode captures light separately and the result is two complete signals being processed simultaneously. The camera takes those two signals and, much like our own two eyes work, uses the difference between the two signals to tell the lens how much to shift before the signals match and the image is considered “in focus.”
For this process to work in the blink of an eye requires two things. The first is a lens that can both communicate with the camera and be controlled by the camera, like any of Canon’s USM or STM lenses. The second is a defined area of your frame to focus on. The sensor must know what you want to focus on because, by nature, large sensors cannot keep the entire image in focus simultaneously, nor would we want them to. On the Cinema EOS Cameras that existed before the EOS C300 Mark II, this area of focus was fixed to the center of the screen. It could not be moved anywhere else. This brings us to the first of five innovations we are going to cover on the EOS C300 Mark II’s Dual Pixel CMOS AF:
- Selectable Focus Point: On the original EOS C100 and C300, the area in which the camera could auto focus to was fixed to the center of the frame. This was acceptable for event videographers and some interview scenarios, but it was limiting when moving into narrative filmmaking. Now with the EOS C300 Mark II, the focus point can be moved anywhere within approximately 80% of the frame, which for all intents and purposes, is the entire frame. The joystick found on the back of the camera, handle unit, and monitor unit, all can move the focus point around the screen much like a video game. Framing to the right thirds? Click, click, click; the camera will now focus on whatever is in the upper right thirds of your frame. You can see this control in action in the video below.
However, filmmakers don’t always want to be restricted to focusing on a fixed point in the image. There may be an object that needs to be tracked throughout the frame, such as an actor or a prop pivotal to the story. There are now two tracking features including in the EOS C300 Mark II that can help filmmakers in a lot of different shooting conditions: Face and Object Tracking.
- Face Tracking: One of the most important things filmmakers capture are faces. Whether it’s an interview or a chase scene, faces are traditionally where filmmakers want their viewer’s attention to go. The EOS C300 Mark II understands that and the Dual Pixel CMOS AF system can recognize faces and automatically keep them in focus. Face Detection and Tracking was first introduced to Cinema EOS in the EOS C100 Mark II, but was restricted to Canon’s STM lenses and relied on less accurate contrast-based focus control. Now in the EOS C300 Mark II, all Canon EF lenses with USM or STM motors can detect and track faces throughout the frame using Dual Pixel CMOS AF. Have multiple faces in a frame? Not a problem. The EOS C300 Mark II can recognize multiple faces, and the user can pick which face to focus on by using the joystick or select dial on the camera as seen in the video below.
- Object Tracking: Faces aren’t always the subjects of a frame and often, for creative reasons, they should not be where the viewer’s attention is at every moment. The EOS C300 Mark II can now track almost any object within the frame. Want focus to hold on a trinket as the subject twirls it through the frame? It’s simple now with the Object Tracking feature built into the EOS C300 Mark II. In the video below, you can see this demonstrated in a mock pivotal moment when a subject hands our protagonist a pen to sign an important document.
- Speed and Response Adjustment: With focus control, it’s not just about getting your subject sharp; there are various other aspects that can affect the emotion that the viewer is supposed to feel. Two major considerations are when the subject starts to come into focus and then how quickly they become sharp. Traditionally, this is a decision left up to an AC (Assistant Camera) and their DP (Director of Photography), but with the EOS C300 Mark II, if there is no AC and the operator must both frame and adjust focus, controlling the response and speed of the Dual Pixel CMOS AF can be incredibly helpful in conveying the overall feel of the shot. The response setting of the autofocus chooses how quickly the subject begins to come into focus and can be set from the slowest of -3 to the fastest of +3. A high setting would be ideal for panning from one subject to another, ensuring the focus adjusts to each subject/object along with the pan (better controlling what the viewer is paying attention to). A low setting might be used in a situation when there are multiple objects crossing frame and the filmmaker doesn’t want to focus on the objects quickly crossing the foreground, but instead keeping focus on the original subject.
The speed adjustment kicks in after the response time and it is used to adjust how quickly the subject becomes totally sharp. A slow romantic rack focus from one face to the other would require a speed of around -7, while a startling rack focus meant to make the viewer anxious would be something like a +2 speed.
- Wi-Fi® Control: The EOS C300 Mark II is also compatible with the existing WFT-E6 wireless transmitter. The WFT-E6 allows the EOS C300 Mark II to be controlled wirelessly from any wirelessly enabled device such as a smartphone, laptop or tablet. The WFT-E6 provides control over all major camera functions, be it white balance or ND filters, but it also allows control of the Dual Pixel CMOS AF system. By pairing the two together, not only will the camera stream a wireless video feed to any wirelessly enabled device, but it allows the filmmaker to simply touch their image and tell the camera where to focus. By using the wireless adapter and a touchscreen-enabled device, we gain the ability to simply “tap” where we want the camera to focus on our image. And while the image on the device is not a zero-latency feed, like something one would expect from a zero latency wireless video transmitter, it is extremely useful for controlling the focus when the camera is out of reach on a jib or gimbal.
The Dual Pixel CMOS AF system is so incredibly impressive that filmmakers from all backgrounds are quickly dropping their preconceived notions about autofocus for video capture. However, while the Dual Pixel CMOS AF system is an impressive tool for continuously keeping the image in focus, that same technology has allowed Canon to design focus assist tools to aid in the manual focus control of lenses for those who would prefer it.
Dual Pixel CMOS AF in the EOS C300 Mark II
Watch examples and scenarios where this Dual Pixel CMOS AF technology can come into play and where you can apply it.