Canon EOS 250D Advanced User's Manual page 222

ISO Speed During Manual Exposure Shooting
With [AUTO], the ISO speed will be set automatically within ISO 100–
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ISO 12800. The maximum limit varies depending on the [Max for Auto]
setting in [z:kISO Auto] setting (= 254). Note that when the
camera is set for 4K movies, ISO speed is ISO 100–ISO 6400.
You can set the ISO speed manually within ISO 100–ISO 12800 in
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whole-stop increments. Under [5: Custom Functions(C.Fn)], if you
set [ISO expansion] to [1:On], the maximum limit of the manual
ISO speed setting range will be expanded so you can also select H
(equivalent to ISO 25600). Note that when the camera is set for 4K
movies, ISO speed is ISO 100–ISO 6400.
If [z: Highlight tone priority] is set to [Enable], the ISO speed
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will be ISO 200–ISO 12800. Note that when the camera is set for 4K
movies, ISO speed is ISO 100–ISO 6400.
Since shooting a movie at ISO 25600 equivalent may result in much noise, it
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is designated as an expanded ISO speed (displayed as "H").
When switching from still photo shooting to movie shooting, check the camera
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settings again before shooting movies.
Changing the shutter speed or aperture during movie shooting is not
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recommended since the changes in the exposure will be recorded.
When shooting a movie of a moving subject, a shutter speed of approx.
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1/30 sec. to 1/125 sec. is recommended. The faster the shutter speed, the
less smooth the subject's movement will look.
If you change the shutter speed while shooting under fluorescent or LED
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lighting, image flicker may be recorded.
If you set [5:Expo comp (hold btn, turn S)] with [Assign SET button]
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under [5: Custom Functions(C.Fn)] (= 452), you can use exposure
compensation with ISO Auto set.
When ISO Auto is set, you can press the <A> button to lock the ISO speed.
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If you press the <A> button and recompose the shot, you can see the
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exposure level difference on the exposure level indicator (= 223) compared
to when the <A> button was pressed.
By pressing the <B> button, you can display the histogram.
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