Lesson 4 of 14 · Module 2: Exposure and Focus
Exposure Lock for Moving Subjects
Lock exposure on a subject’s face using tap-and-hold before a lighting change, then shoot a continuous 10 second clip of the subject walking through mixed light (shade to sun, or sun to shade).
How to Use AE/AF Lock on iPhone: Lock Focus and Exposure for Better Photos
Clean, current (2025) screen-recorded demo of tap-and-hold AE/AF lock plus the brightness slider, on the modern iPhone camera app.
Gap: This shows the AE/AF lock gesture clearly. It does not show the exact scenario in this drill, a subject walking through a real light change with the lock held. Your drill adds the moving subject and the crossing light boundary that this video doesn’t demonstrate.
Objective
Why This Matters
A face vanishing into shadow mid-clip is one of the most common failures in phone video, and it happens because the phone’s auto-exposure reads the whole frame and adjusts for the background, not the person. Your subject walks from a sunny sidewalk into a shaded doorway, and the camera brightens for the new dark background, dropping the face into a silhouette exactly when you needed it visible.
The Technique
On iPhone, open Camera, switch to Video, and before you start recording, tap and hold on the subject’s face until you see a yellow box and an "AE/AF LOCK" banner appear. This locks both exposure and focus to that spot. If the frame still looks too dark or bright after locking, drag the small sun icon next to the yellow box up or down to fine-tune brightness before you roll.
On Android, press and hold on the subject the same way. Look for a lock icon (often a padlock) appearing in the viewfinder. Some Samsung and Pixel phones let you drag AE and AF apart into two separate locks if you want independent control, but the default combined tap-hold lock works fine for this drill.
The key discipline: lock before the light changes, not after. Once you see the face already blown out or gone dark, it’s too late, you’re reacting to a problem instead of preventing it. Watch your subject’s path, identify where the light boundary is, and lock the exposure while they’re still in the starting light.
Keep the lock engaged through the whole clip. Don’t tap the screen again mid-recording unless you mean to relock, since a stray tap will hand control back to auto-exposure.
Watch For This
Good
- Face stays evenly exposed and visible the entire time the subject crosses from shade into sun or sun into shade.
- Background brightness visibly changes behind them while the face brightness holds steady.
- No auto-adjust flare or hunting visible in the first second of the clip.
Classic Failure
- Background exposure "chases" the light change and blows the face to white or drops it into shadow.
- Lock breaks or gets bumped mid-shot, exposure starts hunting again.
- Exposure was locked too late, after the subject already crossed the light boundary.
Your Drill
Find a real light boundary: a shadow line from a building, a doorway, an awning, tree shade meeting open sun. Position your subject (or yourself, walking into frame) so they’ll cross it. Tap-hold to lock exposure on the face while they’re still in the starting light. Roll a continuous, unbroken 10 seconds as they cross. 3 takes.
Pass Checklist
Lesson complete
Criterion met: Face detail stays visible in 9 of 10 sampled frames (sampled roughly once per second) across the full clip.
Coach Note
At the six second mark the face drops into shadow. That’s the light winning because the lock came after the subject already crossed the line. Watch the path this time, lock while they’re still in the sun, and let the doorway happen to the background, not the face.
Resurfaces In
Lesson 9 (Exposure Lock in Low Light, higher difficulty), Lesson 14 (Capstone).