Canon EOS 7D Mark II - live view and movie AF

It's not just the dedicated phase-detection AF sensor that's been updated on the 7D Mark II: the camera's main imaging sensor uses a version of the 'Dual Pixel AF' system first seen in the EOS 70D. This promises to bring significantly improved autofocus in both live view and video shooting.

Canon's schematic of its Dual Pixel CMOS AF sensor structure. The top layer illustrates the light-gathering micro-lenses and conventional Bayer-type color filter array. The lower layer shows how each pixel is split into two photo-diodes, left and right, which are colored blue and red respectively. (Note that this does not indicate different color sensitivity.)

The Dual Pixel AF sensor essentially splits all of its 40 million pixels in half, half of them taking in light from the right hand side of the lens, half taking it in from the left. For the final images, pairs of pixels are combined to give 20 megapixel files sampling all of the light entering the lens. However, the ability to compare the light from the left and right of the lens allows the camera to offer phase detection autofocus whenever the mirror is up. A more in-depth explanation can be found in our EOS 70D review.

Live view autofocus

This system helped give the EOS 70D faster autofocus in live view mode than we'd previously seen from Canon's DSLRs, but it still wasn't as fast as when using the optical viewfinder and the dedicated PDAF sensor. When testing the EOS 70D it wasn't so much the speed as the precision of the Dual Pixel AF system that impressed us - giving much more consistent results than the dedicated AF module could achieve.

Sadly the knowledge of subject distance that this system gives isn't used to provide tracking autofocus in live view mode - like the 70D, the 7D II doesn't attempt to refocus in live view when continuous shooting.

Movie autofocus

Where the on-sensor phase detection is used is during movie shooting. There are three AF point selection modes available during movie shooting mode: Face Detection + Tracking, FlexiZone Multi or FlexiZone Single. In the last of those modes, where the user selects the starting AF position, there are options to control how the camera re-focuses, when combined with Movie Servo AF:

Like the EOS 70D, the 7D II can use the central 80% of its sensor for phase detection, meaning that it can track and re-focus on subjects traveling across that area.

The vertical coverage should be even better in video mode, since the 16:9 footage doesn't make use of the top and bottom of the sensor.

AF Tracking Sensitivity dictates how doggedly the camera will stick with the original focus depth, if something comes between the camera and the subject. There's also an option to control AF speed, so that you can specify how smoothly the camera changes from one focus point to another. During this mode, the flash button on the camera's front panel acts as AF lock, so it should be easy to control when the camera will and won't attempt to refocus.

This continuous autofocus in movie mode only works with certain lenses, however. All Canon lenses with STM motors will work, as will USM lenses launched after 2009. A full list of compatible lenses is available on Canon's web site.

The sad thing is that, unlike the EOS 70D, the 7D II doesn't have a touchscreen. It may sound like an odd thing to look for in such a conventional DSLR but a touchscreen can be an excellent way to re-position the autofocus point during movie shooting. There is an option to use the rear joystick during recording, though.

Using Autofocus in Live View and Video:

Whether you're shooting video or capturing stills in live view mode, the process of using the on-sensor AF system to identify and track subjects is fairly consistent. We'll focus mainly on Face + Tracking mode as it's really the most interesting in terms of how the camera takes advantage of Dual-Pixel AF and what it can do.

With Face + Tracking enabled the system quickly identifies and locks on to a face if one is present in the frame, placing a small size-appropriate square over the face to identify it. If multiple faces are present, the the camera will generally lock onto the most obvious one first, however small arrows will appear indicating that other faces have been detected as well. A simple left or right nudge to the joystick toggles focus through the faces detected in the frame. It's both intuitive and quick.

Face detection recognizes when multiple faces are present in the frame (indicated by the arrows). A tap to the right on the joystick will toggle the focus point to the other face.

If no faces are present in the frame, you can either let Face + Tracking mode automatically select the AF point for you (in which case it reverts to FlexiZone-Multi focus mode), or you can manually select a subject. A quick press of the joystick activates a user-controllable focus square at the center of the frame; placing it over the desired subject and pressing the shutter halfway locks focus on that subject.

Once autofocus is locked onto a face or other subject the AF system diligently tracks it in all three dimensions with a high degree of accuracy. There's a noticeable lack of focus hunting when a subject moves toward or away from the camera. The AF system does a great job of staying with the original target,, and another face or object needs to convincingly take over the frame, or even completely obscure the original subject, before the AF system decides to switch targets.

Dual-Pixel autofocus is slower than the viewfinder's phase detect AF system. While focusing through the viewfinder is lightning quick, focusing in live few is best described as dependable.

Subject tracking is dependable and smooth, but you must place the square over your subject using the joystick.

The joystick-based subject selection system is well designed and effective, but there are times when a touch screen would be helpful; just tap on a subject and be done with it.

The basic implementation of live view autofocus is the same for both stills and video, how one leverages those capabilities in different ways, as we'll explore this on the next few pages.