It is said that eyes are the windows to the soul, and they are the first things we look at when we look at a person’s face. In portrait photography, even if the other features are slightly out of focus, the eyes must be sharp.
Continuous eye autofocus automatically detects and tracks a person’s eye, focusing on the eye first and tries to ensure that at least one eye is in focus. We have loved this functionality ever since Sony implemented it in the a7RII almost three years ago. It is an amazing feature for taking portraits, finding an eye almost instantaneously and keeping track of it in the frame.
Other camera makers have eye detection in AF-S, but with later Sony cameras it is available in AF-C as well. The other advantage of Sony’s implementation is that the on-sensor autofocus does not require microadjustments. If the sensor detects an eye and focuses on it, that eye will be in focus in the resulting photo, because there is no alignment issue with a separate autofocus module as in traditional mirrored DSLRs.
Newer cameras such as the Sony a9, a7RIII, and upcoming a7III, have improved upon the previous iterations of continuous eye AF to be faster and more responsive. They are able to keep up with eye AF even when children are active, but depending on the lens and the situation, it will miss focus a small amount with very shallow DOF.
Because continuous eye AF is a combination of phase detect and contrast detect algorithm, it is a bit slower than phase detect alone. Continuous eye AF is not best suited for action type of photos like swings, sports, running, etc. In those scenarios we would want to switch to using continuous subject tracking (AF-C) and not continuous eye AF. The movements are also several meters/feet at a time instead of centimeters/inches at a time, meaning that the fine tuning of contrast detect autofocus is less useful.
Continuous eye AF is amazing for taking photos of kids who are standing or sitting in one place, but moving their heads and wiggling around constantly. The total depth-of-field is so thin, but the movements themselves are not huge. Here are some examples:
All parents know that 2-year-olds do not hold an expression for very long! The freedom to frame for the shot instead for the autofocus, trusting the continuous eye AF to get the eye, is really valuable.
Eye AF also works when the eye is not horizontal, looking away or looking down. If there are two people in the frame, as long as the eye AF button is pressed down and locked onto the desired eye, it will continue to track that eye.
It’s also fun to be able to have the eyes sharp to the edge of the frame, allowing for more creative choices of framing.
The facial recognition algorithm works with helmets and glasses, although it is not perfect. Some types of hats, especially those with long brims, can throw it off.
When I take posed portraits, I keep my hands on the shutter and hold down the button on the back of the camera I have assigned to eye AF. It allows me to keep connecting with the person, helping the person relax since we do not work with professional models, while not having to worry about the gear or focusing system. This way we can get the best expressions and smiles, and often capture wonderful micro-expressions and fleeting moments.
With continuous eye AF, I can focus on the framing/composition, hold down the eye AF button, and press the shutter button. Is it maybe too easy? I imagine that’s how people felt about the invention of autofocus when manual focus was the main method of focusing, or when exposure meters were first embedded in camera bodies. These are features that photographers can’t imagine going without now. Feature request for the future: animal eye detection for cats, dogs, birds and other wild animals!