Canon EOS 250D Advanced User's Manual page 253

Movie Servo AF
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With this function enabled, the camera focuses on the subject
continuously during movie shooting. The default setting is [Enable].
When [Enable] is set:
- The camera focuses on the subject continuously even when you are
not pressing the shutter button halfway.
- If you want to keep the focus at a specific point or if you do not want
the lens mechanical sound to be recorded, you can temporarily stop
Movie Servo AF as follows.
• Tap [Z] on the screen's bottom left.
• Under [5: Custom Functions(C.Fn)], if [Shutter/AE lock
button] is set to [2:AF/AF lock, no AE lock], you can pause the
Movie Servo AF while holding down the <A> button. When you
let go of the <A> button, Movie Servo AF will resume.
- When Movie Servo AF is paused, if you return to movie shooting
after operations such as pressing the <M> or <x> button or
changing the AF method, Movie Servo AF will resume.
When [Disable] is set:
- Press the shutter button halfway to focus.
Cautions When [Movie Servo AF] is Set to [Enable]
Shooting Conditions that Make Focusing Difficult
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- A fast-moving subject approaching or moving away from the camera.
- A subject moving at a close distance to the camera.
- For details, see "Shooting Conditions that Make Focusing Difficult"
(= 202).
Since the lens is driven continuously and battery power is consumed, the
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possible movie shooting time will be shortened.
With certain lenses, the mechanical sound for focusing may be recorded. In
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such a case, using Directional Stereo Microphone DM-E1 (sold separately)
may reduce such sounds 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 that is recorded.
Movie Servo AF will pause during zooming or magnified view.
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During movie shooting, if a subject approaches or moves away or if the
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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
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AF, first set the camera's power switch to <1>.
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