What do ae-l and af-l mean?

AE-L is locked exposure and AF-L is locked focus, that is, even if the shutter button is released after pressing this button, the exposure and focus will not change. When you select this button in the settings menu, you can only lock the exposure or focus, or you can lock it together. You can even choose to press it once and keep it locked until you press it again. Using this function, it is convenient and accurate to recompose the composition after photometry.

Specific usage:

When defining the metering mode for the camera, the camera will get a set of aperture/shutter parameters according to the brightness of the picture, such as 1/200 F2.8. Press the exposure lock, and this set of values will not change for a certain period of time, so as to accurately represent the subject when shooting the Gao Fancha scene.

Taking spot metering as an example, the operation steps are as follows: find the subject from the view frame, move the camera to make the subject fill the spot metering area, half press the shutter to focus, press the exposure lock key, and move the camera to re-compose.