Canon 30D - Manual (Page 14)

Page 14 of 35 © Ken Rockwell 2006
Top Rear Corner
* (star), Checkerboard, (-) Button: This is on the top right of the rear of the
30D.
In playback: Zooms out (-), or if you're zoomed all the way out, the next push
gets you into the 9-image display mode (checkerboard).
During shooting: * is Exposure Lock. Press * to lock the exposure. You'll see
"*" in the finder to confirm after you've pressed it. This is the easy way to set
the exposure in difficult (contrasty or backlit) light by pointing at one subject,
locking the exposure and recomposing.
For instance, with strong backlight, zoom into the face, tap the * (see "*" in
finder to confirm that the exposure is locked) and zoom back out and
recompose for your photo. This is much faster than other ways of setting
exposure. Of course in a backlit case you should be using fill flash, too.
It should be marked AEL. Sorry.
You can change the function of this button in Custom Function 04.
Once locked, it stays locked. I wish it unlocked if I pressed * again. Pressing it
again merely locks it to a new setting Even taking a picture won't release it.
You have to press one of the top AE-WB or DRIVE-ISO buttons to release it.
If your flash is on, it locks flash exposure, too. You'll see FEL (Flash Exposure
Lock) blink in the finder right after you press it.