It's Time to Admit It: It's OK to Use Autofocus for Video

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I can picture the eyerolls after reading that headline, and I totally understand. Will the cinematography departments of digital films now utilize autofocus in their carefully planned, meticulously lit, and choreographed productions? No, and for many reasons other than to keep focus pullers employed. But, using AF technology in smaller films, documentaries, reality shows, sporting events, and streaming productions can benefit greatly by the use of autofocus for their shots, so the camera won’t lose focus when a compact crew is busy juggling five jobs on a limited schedule.

The truth is that autofocus will never be perfect. And not all lenses support autofocus, especially most high-end cinema prime lenses. But the technology has advanced so dramatically, video camera operators have been successfully using tech like dual-pixel autofocus for years now, with lenses that have built-in autofocus support. More autofocus support has been added to cinema cameras in recent years, and the tracking accuracy and facial recognition features have dramatically improved.

There are several situations in which autofocus makes little to no sense, if you already have timed or slow focus adjustments, or if you have a focus puller who is working on a complex sequence that needs patience, precise blocking, and constant adjustment. Also, if you are using specific primes with manual focus and have your setup tuned for that lens line, it is impractical to slow the production down just to swap in an autofocus lens for a brief shot or two.

Situations in which you’d want to use autofocus are plentiful; scenes with a single or small number of roving subjects, especially in documentary projects, walk-and-talk interviews, or sports, or when constant light changes have your sole camera operator trying to change the iris simultaneously. Or maybe when you set your camera to operate on its own while mounted in a car or on a tracking vehicle and may not have available remote-control options. With 4K video being the norm with cine cameras, it is next to impossible to focus with the naked eye, so learning the autofocus functions on your cinema camera can be a great help when using large formats, as it has been to photographers.

Canon CN-E 18-80mm T4.4 COMPACT-SERVO Cinema Zoom Lens
Canon CN-E 18-80mm T4.4 COMPACT-SERVO Cinema Zoom Lens

On the lens side, cinema lenses with autofocus functionality are still very sparse in the field since tradition often holds back innovation. You will have to utilize photography-style lenses that support autofocus on their cinema cameras (see our selecting an autofocus lens article). However, recently Canon introduced its line of CN-E cine servo lenses, and Sony’s E-mount cine lenses, designed for large-format cameras and 4K production, have servo control that features a drive unit that can control the focus, iris, and zoom. Focus pullers will also like these lenses because instead of changing the lens, they can remove the servo unit for manual operation. The CN-E lenses work with the camera to follow the desired subject using dual-pixel phase-detection AF. Rokinon also offers an AF line of cine primes for E-mount cameras, and GLOBAL DYNAMICS UNITED features EF-mount electronic-only lenses that work with Canon autofocus control.

So, what is phase-detection AF? The technology was originally developed for SLRs, and it detects and compares slight changes in light wavelengths coming into the camera for each pixel to adjust focus, which is an improvement in speed and accuracy over its relative, contrast detection. Phase detection also informs the camera which direction to turn the focus wheel, so it doesn’t swing back and forth the way it does with contrast-based detection. “Dual-pixel” phase detection is a fine-tuning feature that compares two photodiodes side-by-side within each pixel to compare wavelengths. This allows the sensor to detect focus and light changes quickly, down to micro levels. Canon allows you to use this technology in Live View mode, which helps apply it successfully to video capture. Many cameras also have subject tracking and facial detection features to help you hold focus when capturing movement. Canon cinema cameras that utilize phase detection AF include the EOS C200, C300 Mark III, C500 Mark II, and C70.

Canon EOS C70 Cinema Camera with One Shot AF
Canon EOS C70 Cinema Camera with One-Shot AF

Sony also developed Fast Hybrid AF that is used on its cinema cameras, such as the FX6 and FX9, which combines contrast detection and phase-detection AF for quick tracking with great accuracy when tracking very fast-moving subjects, and it also includes face and subject detection. However, Fast Hybrid only supports compatible Sony lenses, so if you use other AF lenses with one of these cameras, it will default to contrast detection, which may not track objects as accurately. The FX3 utilizes Advanced Alpha Hybrid AF, developed for higher-end mirrorless Alpha cameras such as the a7S III, which combines hybrid AF with speed, real-time face tracking, shift sensitivity (how easily you want the camera to shift its focus to a different subject), transition speeds for shots like rack focus, and touch tracking to alter your settings on the fly.

Other cinema cameras that utilize a basic “one-touch” autofocus mode without the additional subject tracking technology include Z CAM E2 series and Panasonic AU-EVA1 cameras that allow you to use AF mode with a compatible lens. New autofocus features aren’t necessarily “set it and forget it” settings, so you aren’t completely giving over your control. The usefulness of zones, touch tracking, and transition speed relies on your interaction and input, so AF isn’t going to take over your custom-focus needs.

The technology still needs to advance further to provide a high level of accuracy, control, and customization. When using AF, cinema cameras still require a lot of trial and error when it comes to low-light conditions, changing environments, and super-fast subjects, but there are now real possibilities to make your life easier when it isn’t possible to have a crack focus puller by your side.

Check out our video for more information on the differences between phase and contrast autofocus.

Have you used autofocus on a cinema camera to shoot any of your scenes? Used any of the latest facial tracking features or shift sensitivity? Tell us about it in the Comments section, below.

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I guess if you're using a Sony camera such as the A7C or the A7S3 autofocus in video is fine. If you're using Panasonic cams, well, you better use manual focus.

It depends on the situation and lens type you're using whether AF will help with the shot. The AF on e.g. a Panasonic EVA1 doesn't have all the bells and whistles as the latest Sony AF, but if it might help your scene,  an AF-capable / cine servo lens might be just the thing to set up your AF shot.

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