04-15-2021 - Gear, Technology
Sony’s Autofocus Settings Explained
By: No Film School
In collaboration with No Film School.
A helpful guide to the different AF functions found on the Sony Cinema Line.
In the early days of digital video capture, autofocus was indeed a technological breakthrough. And as tech has evolved, manufacturers like Sony have made great strides to help turn autofocus from something that was somewhat unreliable into a necessity.
When it comes to autofocus, there are a lot of different acronyms behind the various settings and functions: AF, Hybrid AF, Eye-AF, Face-Detection, Animal-AF, among others. But what do all these different names and letters actually mean?
With Sony's Cinema Line of cameras that include VENICE, the FX9, FX6, and FX3, the company has implemented the Fast Hybrid AF found on its popular Alpha series, which combines phase detection autofocus and contrast detection autofocus in one system.
Let's break down the major autofocus features and what each setting means.
Phase Detection AF
Phase detection AF (PDAF) has changed the autofocus game tremendously. Phase detection AF works by splitting the light entering the camera into two separate images and analyzing them for similar light intensity patterns and calculating the amount of focus needed to adjust.
PDAF is depth-aware, allowing it to quickly switch between objects. It's great for fast-moving objects and why it's critical video-based cameras implement a form of PDAF, especially when trying to use autofocus at 4K 120fps.
Contrast Detection AF
Contrast detection AF works by analyzing pixels to measure when contrast is at its highest. Contrast AF is great for its precision, but it's challenged in terms of speed. It’s depth finding, but it’s not depth aware. So when you have two objects at different depths, it is physically unable to tell the difference between the two.
Contrast detection AF is generally considered to be slightly slower, but more accurate than phase detection AF.
Phase Detection Points
To calculate focus, cameras generally have a set number of Phase Detection Points, which are used when comparing images while autofocusing. For example, if the Sony FX3 has 627 phase detection points, it means that there are 627 spots that cover the sensor where it can compare for focus.
Focus Control Touch
Focus Control Touch is a more advanced feature of autofocus control. When using a Sony FX camera, all you have to do is touch the subject on which you want to focus before or during recording. When you touch the subject, the focus mode temporarily switches to manual focus and the focus can be adjusted using the focus ring. To cancel spot focus, touch or press the center of the control wheel.
AF Transition Speed
AF Transition Speed allows you to select the focus speed while recording movies with your Sony cameras. This function enables focusing on a subject quickly or smoothly. You can change the focus speed without compromising the performance of tracking a subject.
AF Subject Shift Sensitivity
With AF Subject Shift Sensitivity, you can select the sensitivity of keeping the focus on a subject while recording movies. This function enables keeping the focus on a particular target without being affected by other subjects or shooting multiple subjects located at different distances while switching the focus smoothly from one subject to another.
AF Transition Speed and AF Subjective Shift Sensitivity are available on the FX9, FX6, and FX3, and are massive breakthroughs when it comes to autofocus performance. They give you the ability to focus automatically between subjects with remarkable precision.
In our tests with the FX9 and FX6, the AF features have produced excellent results that give the appearance of a handheld rack focus. It even works tremendously well in low light, which is extremely helpful as a single shooter.
Your Focusing Area is how your camera knows where in a scene to direct focus. It allows you to pick a certain area in your frame to use as your focus point.
Focus Area (AF-S)
For Sony cameras, you can select a Focus Area either with single mode (AF-S) or continuous mode (AF-C). Single modes will put the focus exactly where you have placed your focus point in your viewfinder, while continuous mode will adjust focus continuously.
Face Detection AF
Face Detection AF is as its name implies and uses face detection technology to keep human faces in focus. When shooting stills, Face Detection AF focuses on the faces of your subject and optimizes exposure and white balance.
Similarly, Eye AF is also as its name implies, and uses eye detection technology to keep eyes as the point in focus. When enabled, the autofocus system will place a box around the eye as it tracks focus. Sony’s Eye AF continuously tracks not just your subject, but the individual eye, making sure your subject is tack sharp no matter the frame rate. When shooting still, Eye AF does not optimize exposure or white balance.
An extension of Face Detection AF, Sony has real-time tracking of animals through Animal AF. The AI-based subject recognition technology used in Sony's real-time Eye AF feature has been augmented with a new algorithm that supports animals in addition to humans. This enables fast, precise, automatic detection and tracking of the eyes of various animals like cats, dogs, and birds. Animal AF is even able to continuously work through partially obstructed views like through windows, a person's hand, trees, bushes, or similar obstacles.
Push AF Mode
Push AF Mode is the method where focus is set automatically when the button is pushed while in manual focus mode. Focusing occurs within the focus area set in the menu. The focus returns to manual focus when you release the button. This is useful when you want to move the focus slowly from one subject to another subject during manual focus.
Those are some of the basic terms and technologies associated with autofocus in the Sony Cinema Line. As more Alpha features make their way into the Sony FX9, FX6, and FX3, moving from the Alpha platform to Cinema Line will be a seamless transition.
Autofocus has become a valuable tool for creators and shouldn't be overlooked for any sort of indie, corporate, commercial film, documentary film, or video project.