How does Canon 50D display histogram in real-time shooting?

First of all, about camera shutter settings.

Among the five types of settings, the auto-focus function is only effective when the focus mode is automatic, and it is invalid when focusing manually.

0 metering+autofocus start

1 metering+autofocus start/stop

2 metering start/metering+autofocus start

3 Automatic exposure lock metering+autofocus start

4, metering+autofocus on/off

How should I usually set it up?

Second, real-time shooting.

Camera settings: start the real-time shooting function, and take one shot in focus mode.

1. After manually zooming in and focusing, re-compose.

Use 50D real-time shooting function: set the focusing mode as: real-time non-fast or real-time face, focusing mode as: manual focusing,

When shooting, the instruction manual prompts to manually focus the place that needs to be focused with the "zoom button". First, I zoomed in where I needed to focus. If I want to re-compose, I tried how to lock the focus. After manually zooming in and focusing, I gently press the shutter to image! ! ! I can't seem to repaint.

2. Use the 50D real-time shooting function: set the focus mode to: Real-time mode means real-time face, and the focus mode is autofocus, and there is no green frame, only black.

Third, the meaning of this passage.

Separate the operation of autofocus and automatic metering to obtain more correct exposure.

In portrait photography, focusing and determining exposure parameters are very important. The default setting of the camera is that when the shutter button is half pressed, autofocus and automatic metering will be carried out at the same time. But in some scenes, it is more convenient to separate autofocus from automatic metering, such as portrait photography. So it is best to separate the control buttons of the two functions.

You can set the shutter button to auto-exposure lock in the settings of custom functions, and assign the auto-focus function to the auto-focus start (AF-ON or auto-exposure lock) button. By separating autofocus from automatic metering, the photographer can decide the automatic exposure parameters after autofocus is completed and the final composition is arranged.

If "Shutter Button/Auto Focus Start" (AF-ON or Auto Exposure ..... is in the custom function menu, does it mean that auto focus will be started when the AF-ON key is pressed? And how to lock the focus after this setting.