Exposure: no blown-out highlights, no dark face

You've set up the light, you're standing in the right spot, and your face on video is still either too dark or washed out, and it flickers every time you move. Your light is fine. The phone is just deciding on its own how bright to show it, and it often gets that wrong. This lesson is about deciding for yourself.

What it is, without the physics

Exposure is how much light the camera lets onto the sensor. Too much and the frame goes bright, eventually white, and detail in the bright areas disappears. That's called clipping or blowing out. Too little and the frame goes dark, with noise in the shadows.

By default the phone looks at the whole frame and picks an average brightness. Newer phones try to find a face and adjust for it, but with a big bright window next to you the automation often gets it wrong: it decides there's loads of light and turns exposure down. The window looks lovely. You look dark.

The auto mode that breathes

Second symptom: brightness drifts. You raise your hand, a bit more bright wall enters the frame, the phone readjusts, and your face dims for a second. You lower your hand, it brightens again. Viewers don't consciously notice, but they feel the picture pulsing.

One gesture fixes it. Tap on your face on the screen and hold your finger there for a second or so. An AE/AF Lock banner appears on iPhone; on Android the wording depends on the maker, but there's usually a padlock icon. Now brightness and focus stay put until you tap the screen again, switch cameras or leave the app. Changed the light or moved your seat? Lock it again.

If you're filming yourself, you can't tap on your own face: you're not in the frame yet. Do this instead: put a chair or any object at head height where you'll be, tap and hold on it, lock, remove the object and sit down. Then shoot a five-second test and adjust the brightness slider by your own face: a chair has no skin, so the brightness will be off. After that, don't change your distance to the camera, or focus will drift.

Do this before every take. It's a three-second habit, and the picture stops breathing.

Set it by the face, not the background

Once locked, a slider with a little sun usually appears next to the focus box. That's manual brightness compensation. Drag up for brighter, down for darker.

The rule: look only at your face. The background can fall into darkness or blow out, that's fine. Your face should be bright but with visible skin texture. If a white patch with no detail appears on your forehead or nose, that's clipping, bring it down a bit. If everything under your eyes merges into black, bring it up.

Tip. Slightly dark beats slightly bright. A dark shot can be lifted a little in editing, though noise creeps into the shadows, so don't go too far. Blown-out white areas can't be recovered by anything: there's simply no information there.

The window behind you

Sometimes you really want the window in the background: a nice view, plants, light. Here's what you can do.

The simplest option: don't shoot against the window. Turn 90 degrees and the window is beside you. The view won't be in the shot, but your face will.

Second option: balance the light. In daytime the window behind you is very bright, and to keep your face from going silhouette, you need nearly as much light hitting it from the front. That's a second window opposite, or a lamp with a neutral white bulb. Don't use a warm yellow one here, or you get the colour mix from lesson one. Without light from the front it won't work.

Third option: shoot on an overcast day or towards evening when the window isn't as bright, and set exposure by your face. The window will blow out to a white patch, but your face will be fine. Sometimes it even looks good.

Do this now

• Open the camera, point it at yourself, tap and hold on your face until the lock appears.
• Drag the brightness slider up and down. Find the point where you can see skin on your face rather than a white patch.
• Stand with your back to a window and watch what auto does. Then lock exposure on your face and compare.