Canon EOS REBEL T7i Instruction Manual page 304

3 Menu Function Settings
Cautions When [Movie Servo AF] is Set to [Enable]
Shooting Conditions that Make Focusing Difficult

• A fast-moving subject approaching or moving away from the camera.
• A subject moving at a close distance in front of the camera.
• Also see "Shooting Conditions that Make Focusing Difficult" on page
254.
Since this drives the lens continuously, it will consume battery power and

shorten the possible movie shooting time (p.276).
With certain lenses, the mechanical sound for focusing may be recorded.

If this happens, using the Directional Stereo Microphone DM-E1 (sold
separately) may reduce the lens mechanical sound in the movie. Also,
using certain USM lenses (for example, the EF-S18-135mm f/3.5-5.6 IS
USM) or certain STM lenses (for example, the EF-S18-55mm f/4-5.6 IS
STM) will reduce the lens mechanical sound to be recorded.
Movie Servo AF will pause during zooming or magnified view.

During movie shooting, if a subject approaches or moves away or if the

camera is moved vertically or horizontally (panning), the recorded movie
image may momentarily expand or contract (change in image
magnification).
If you want to set the lens's focus mode switch to <MF> during Movie

Servo AF, first set the camera's power switch to <1>.
AF method

The AF methods are the same as described on pages 247-256. You
can select [u+Tracking], [Smooth zone], or [Live 1-point AF].
Metering timerN

You can change how long the exposure setting is displayed (AE lock
time).
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