Beginners may wonder what the AE-L/AF-L or the “*” button on their camera is for.
Here’s what. It’s called “exposure lock”.
It allows you to do the following:
- Aim at something you want to expose well (a mid0greay object, ideally);
- Press the lock button;
- While still holding it down, now recompose (i.e. aim the camera at another area);
- The focus and click.
That way you get a picture that is focused on what you set as the final composition, but its exposure is based on where you were aiming earlier, when you pressed the lock button.
You might use this if shooting a person against a very white or dark wll. Aim at the person, lock, now aim back at the rest of the scene, now takethe image The exposure will be based on the person, not on the wall.
Two things you need to be sure to do for this to work:
- Set your meter to spot metering.
- While locking, be sure to aim at an object that is not very dark nor very light – an “18% grey” object, like a Grey Card or like Uncle Fred’s grey suit.
Do this and all your images will be exposed great.
So why do we not use this all the time? Simply because it takes time.