Airplane. AE is automatic exposure measurement, and A(AUTO) means automatic.

AF is autofocus.

AE-L is the exposure lock, and L is the lock, so the characters will appear very dark when you shoot the backlight. At this point, close to the person and focus, measure the light of the person's face (half press the shutter). At this time, AE and AF are locked at the same time, but we only need to lock AE, not focus lock. At this time, colleagues will hold AE-L and then release the shutter. At this time, the aperture and shutter have been locked by AE-L when you press the shutter first, then release AE-L, and then press the second shutter to image. In fact, this principle is very simple, just like a picture on a white wall. If you press the shutter halfway on the screen, it means focusing and metering. But now we have to measure the light of the white wall, but focusing is to focus on the painting. At this time, press the shutter on the white wall, then press AE-L to lock the exposure value, move the camera to focus on the painting, and then press the shutter.