Eye Detection AF: Better Portraits with Auto Focus

Eye detection AF is an autofocus setting that finds an eye in the frame and puts focus on it for you, then keeps it there as the person or animal moves. It matters because the eye is where a viewer looks first in a portrait, and at the wide apertures portraits are often shot at, the zone of sharp focus can be only two or three centimetres deep. Miss the eye by the width of a nose and the picture reads as out of focus, even if the ear is crisp.

Eye detection does not make the camera focus better. It decides where the camera focuses, quickly and without you moving a point. Knowing that difference, and knowing when the camera picks the wrong spot, is most of what it takes to use it well.

What eye detection actually does

Every autofocus system answers three separate questions: when to focus (single or continuous), where in the frame to look (the AF area), and what to look for. Eye detection is an answer to the third question. A recognition model in the camera’s processor, trained on a very large number of pictures of faces and eyes, looks at the live image from the sensor many times a second and reports where it thinks the eyes are. The camera then moves the active focus area onto that eye.

After that, focusing works exactly as it always does. On-sensor phase detection, contrast detection or a mix of the two measures the distance to the eye and drives the lens. So eye detection fixes one kind of miss, the camera focusing on the wrong thing, and does nothing for the others: a subject moving faster than the lens can follow, a shutter speed too slow to stop shake, or a depth of field too thin for what you wanted sharp.

Want to know how the camera measures distance once it has found the eye? How autofocus works explains phase detection, contrast detection and the hybrid systems that do the measuring.

Body, face, eye: the detection cascade

Many current systems do not look for an eye directly in the whole frame. They find the biggest, easiest shape first and narrow down, as the diagram above shows. A body can be recognized when the person is small in the frame. A head or face needs to be larger. An eye needs to be larger still, and visible. As the subject comes closer or turns toward you, the box on screen shrinks from body to face to eye. When they turn away, put on sunglasses or walk into shadow, it grows back out.

That is why eye detection seems to “work sometimes”. It is always working; it is reporting the smallest thing it can recognize with confidence. Watching the box tells you which level it is at, and therefore how precise the focus will be. A box on the face at f/1.8 can land on the nose or the cheek. A box on the eye usually lands on the eye.

Face detection, eye detection and eye-controlled AF

Three features get mixed up. Face detection is the older, coarser level: it finds a face and focuses somewhere on it, usually the nearest feature with good contrast. Eye detection goes one step further and picks an eye. Eye-controlled AF, offered on a few cameras, is something else entirely: an infrared sensor in the viewfinder watches the photographer’s own eye and moves the focus point to wherever you are looking. It chooses the subject; it does not focus on anyone’s eye unless you look at it.

People, animals, birds

Detection models are trained per subject type, so cameras usually offer a choice: people, animals (which typically means cats and dogs and similar mammals), birds, and sometimes vehicles, or an automatic mode that switches between them. Animal and bird eyes are harder: they vary more in shape, sit in dark fur or feathers, and are often small in the frame. Expect the camera to fall back to the head or body more often with animals than with people, and pick the matching subject type rather than leaving it on people when you photograph a dog.

Photographing animals that will not sit still? Wildlife photography covers fieldcraft and long lenses, how to photograph birds covers birds in flight, and pet photography covers getting a cat or dog to look at you.

Which eye: why the near eye usually wins

Facing the camera straight on, both eyes are the same distance away and either one will do. Turn the head and they are not. Adult eyes are about 6.3 cm apart, centre to centre. Turn the head 45 degrees and the far eye sits about 4.5 cm farther from the camera than the near one (6.3 × sin 45°). At 30 degrees it is about 3.2 cm; in full profile the far eye is hidden.

Now compare that with how deep the sharp zone is. The table shows the total depth of field for an 85mm lens on a full-frame camera with the face 1.5 m away, about a head-and-shoulders portrait, using the usual 0.03 mm circle of confusion:

Focus on the near eye with the head turned 45 degrees and the far eye is 4.5 cm behind the plane of focus. At f/1.4 the sharp zone reaches only 1.2 cm behind it, so the far eye is clearly soft. Only at about f/5.6 does the zone reach back 5.1 cm and take in both eyes. Get it the other way round, with focus on the far eye at f/1.4, and the near eye, the near cheek and the near eyelashes all go soft, which looks like a mistake because the nearest part of a face is where the viewer expects sharpness.

Cameras with eye detection usually let you choose Auto, Left or Right. Auto generally picks the eye nearer the camera or the one it can see most clearly, which is right most of the time. It can switch eyes between frames when the head is nearly square to the camera, and it can choose the far eye when hair, a hand or a reflection hides the near one. When the head is turned and you are shooting wide open, check which eye has the box, and if your camera lets you, switch eyes with a button rather than hoping.

Placing focus between the eyes and stopping down so the zone covers both is the other option. It works when you want both eyes sharp, but it needs the aperture that covers the full 4.5 cm with room to spare, and most cameras will not let you aim eye detection at “between the eyes”. Use a single AF point for that.

Want to see how distance, focal length and aperture change these numbers? The depth of field calculator works them out for your own lens, and depth of field explains why the sharp zone is so thin up close.

How close you are changes everything

Depth of field changes with the square of the distance, so moving closer thins it fast. The same 85mm at f/1.4 from 1 m, a tight headshot, gives a total depth of about 1 cm, half a centimetre either side of focus. At that range even the difference between the eyelashes and the iris, a few millimetres, matters. The eye box sits over the whole eye, and the measured spot inside it can be the lashes or the lid, which have more contrast than the iris. If the lashes are sharp and the iris is not, open the picture at 100 percent and you will see it. Stop down a third or half a stop for tight headshots, or step back a little.

From 3 m at f/1.4 the same lens gives about 10 cm, and the choice of eye almost stops mattering. Full-length portraits and groups are far more forgiving than headshots.

Remember that focus is a flat sheet, not a point: the focal plane runs across the whole frame at the distance of the eye, and slices through the face wherever that distance falls.

How to set up eye detection

Menu names differ, but every system has the same handful of settings. Set them once and most of the work is done.

1. Turn subject detection on and choose the subject. Look in the autofocus menu for a setting called subject detection, face/eye detection, eye AF or similar. Pick people, animals or birds to match what you are photographing, or Auto if your camera offers it and you shoot a mix.
2. Choose the eye. Auto for most work. Left or Right when you are working a pose with the head turned and want it to stay put.
3. Use continuous AF (AF-C, Servo). Even a seated person sways a centimetre or two while breathing and talking, which is most of the sharp zone at f/1.4. Continuous AF keeps correcting right up to the moment the shutter opens. Single AF (AF-S, One Shot) locks once and stops, so the sway is not corrected.
4. Give the camera room to search. A wide or whole-frame AF area lets detection find the eye anywhere. On many cameras detection only works inside the area you set, so a single point in the corner will stop it finding a face in the middle. With several people in the frame, a zone or a tracking point lets you tell it which person to look at.
5. Put an override on a button. Set one button to switch to a single AF point, or to turn detection off while held. When detection grabs the wrong thing you want the fix under your thumb, not three menus deep.

On a phone, eye and face detection are usually on all the time. Tapping a face tells the phone which person to follow. Phone sensors are small, so their depth of field is far deeper and the choice of eye rarely matters, unless you use portrait mode, which blurs the background in software after the picture is taken.

Want focus on a different button from the shutter? Back button focus moves autofocus to your thumb, which pairs well with eye detection: hold to track, release to stop.

Reading the boxes in the viewfinder

Most cameras draw a thin box when they detect a face or eye and change its colour or weight when they have focused on it. A box on a face but not an eye means the camera is working at the face level. A box that jumps between two people means it cannot decide which to follow, so narrow the AF area or select a face. A box that disappears means the subject is too small, too dark or turned too far away, and the camera has fallen back to the AF area you set.

A box on the eye means the camera is trying for the eye. It is not proof the eye is sharp. Check on the camera screen by zooming in on the eye in a few frames, especially early in a session and whenever the light changes.

Where eye detection helps most

• Portraits at wide apertures. The thinner the sharp zone, the more it helps. At f/1.4 to f/2.8 it hits the eye more often than most people can with a moved point, and it frees you to watch expression and composition. See portrait photography and headshots for the rest of the picture, and catchlights for the light that makes a sharp eye look alive.
• People who move. Children, dancers, a couple walking toward you, a speaker pacing a stage. Continuous AF with eye detection follows them around the frame without you steering a point.
• Events and weddings. Fast, unrepeatable moments with faces at many distances. Detection lets you recompose freely while focus stays on the person. Event photography and wedding photography cover the rest of the work.
• Candids. When you have half a second, not having to place a point is the difference between getting the frame and not. Candid photography covers how to be ready.
• Animals and birds close enough to show an eye. A dog running toward you or a bird filling a good part of the frame. Far-off wildlife is often too small for eye level detection.

When eye detection gets it wrong, and what to do

The camera fails in predictable ways. Each one has a reason, and knowing the reason tells you the fix.

• Sunglasses, deep hat brim, hair across the eyes: What the camera does: Cannot see an eye, falls back to the face or head. What to do: Stop down a little so the whole face is sharp, or put a single point on the frame of the glasses.
• Clear glasses with reflections: What the camera does: Can focus on the glare or on the frame, which sits about 1 to 2 cm in front of the eye. What to do: Tilt the glasses or move the light to kill the reflection, then check at 100 percent.
• Head in near profile: What the camera does: Drops from eye to face, or picks the visible eye late. What to do: Use a single point on the visible eye, or turn the head back a little.
• Face small in the frame: What the camera does: Works at body or head level only. What to do: Move closer or zoom in; at that size the depth of field is usually forgiving anyway.
• Low light or strong backlight: What the camera does: Detection slows or loses the eye; a silhouette has no eye to find. What to do: Add light on the face, raise exposure on the face, or focus with a single point on an edge at the same distance.
• Several people: What the camera does: Picks the nearest or largest face, maybe not the one you want. What to do: Narrow the AF area, select the face with the joystick or touch screen.
• Faces that are not people: What the camera does: Locks onto a poster, statue, mannequin or a pattern that looks like eyes. What to do: Narrow the AF area or switch to a single point.
• Someone walks between you and the subject: What the camera does: May jump to the new face. What to do: Lengthen the tracking sensitivity (blocked subject) setting so the camera waits.

Face detection can also feed the metering. Many cameras weight the exposure toward a detected face, which is usually what you want in a portrait and can surprise you when the camera finds a face you did not intend.

Is the trouble with autofocus in general rather than eye detection? How to fix common autofocus problems works through hunting, wrong-subject locks and front or back focus one by one.

When detection keeps failing, focusing by hand is often faster than fighting it. This challenge in the Camera Simulator asks you to do exactly that on a portrait, using peaking at f/2 or wider:

Common mistakes with eye detection AF

• Trusting the box without checking. The box shows the target, not the result. Zoom in on a few frames.
• Using single AF for portraits. AF-S locks once; the sway that follows can move the eye out of a 2.5 cm sharp zone before you press the shutter. Use continuous AF.
• Leaving the eye on Auto at f/1.4 with the head turned. Auto usually picks the near eye but not always. Look at which eye has the box.
• Expecting both eyes sharp wide open. With the head turned 45 degrees at 1.5 m on an 85mm lens, both eyes need about f/5.6. Choose the aperture for the pose.
• Blaming focus for motion blur. A sharp eye box and a soft picture usually mean the shutter speed was too slow. Focus cannot fix shake. See how to take sharp photos.
• Using a single small AF area. On many cameras detection only searches inside it, so it never finds the face.
• The wrong subject type. Detection set to people will struggle with a dog’s eye. Match the setting to the subject.

Want to test what you know about AF modes, points and detection? Try the camera focus and autofocus quiz.

Try this: find your camera’s limits in ten minutes

You need a willing person, or a pet that will sit, and a window for light. Use your widest aperture, continuous AF, eye detection on and the eye set to Auto.

1. The turn (3 minutes). From about 1.5 m, take a frame with the head facing you, then at roughly 30, 45, 70 and 90 degrees. Note which eye the box is on in each, and where it gives up on the eye.
2. The distance (2 minutes). Walk back a step at a time until the eye box becomes a face box, then a body box. That is the face size your camera needs.
3. The glasses (2 minutes). If your subject wears glasses, shoot with and without, and with the glasses tilted slightly down to kill the reflection.
4. The light (3 minutes). Move the person away from the window into the darkest corner of the room, and then stand them against the window as a backlight.

How to judge it: open every frame at 100 percent on the eye. Count how many have the iris sharp, not just the lashes or the eyebrow. In the turn frames at f/1.4 to f/2, the near eye should be sharp and the far eye soft from about 30 degrees on; if the far eye is sharp and the near one soft, the camera picked the wrong eye. The angle, distance and light where your hit rate falls are your camera’s limits. Beyond them, switch to a single point or manual focus.

Eye detection AF questions

Which cameras have eye detection AF?

Almost every mirrorless camera made in recent years has it, because the autofocus sensor is the image sensor and can see the whole frame. DSLRs generally offer it only in live view, using the rear screen, and a few can detect faces through the viewfinder using the metering sensor. Most phones detect faces and eyes too. DSLR, mirrorless and point-and-shoot cameras explains why the camera type matters.

Should I use AF-S or AF-C with eye detection?

AF-C for nearly everything, including still portraits. It keeps correcting for small movements until the shutter opens, which matters when the sharp zone is a couple of centimetres deep. Continuous autofocus explains how it predicts movement.

Does eye detection work with glasses?

Usually, yes, with clear glasses. Strong reflections on the lenses can pull focus to the glare or the frame, which sits in front of the eye. Dark sunglasses hide the eye, so the camera falls back to the face.

Does eye detection work for video?

Yes, on most cameras that have it for stills, and it is often the most useful focus setting for a person talking to the camera. Set a slower focus transition so focus does not snap visibly when the camera switches eyes or faces. See camera settings for video.

Why is the eye box green but the eye soft?

Either the camera focused on the lashes, lid or glasses instead of the iris, the subject moved after focus, or the softness is motion blur from a slow shutter speed. Zoom in: if the eyelashes are crisp, it was focus placement; if everything is smeared in one direction, it was movement.

Is eye detection the same as tracking?

No. Tracking follows whatever you put the point on, by its colour, pattern and shape. Eye detection recognizes eyes specifically. Many cameras combine them: tracking holds onto the person, and detection finds their eye whenever it is visible.