Canon EOS 6D Instruction Manual page 209

ISO speed during manual-exposure shooting
With [Auto] (A), the ISO speed will be set automatically within ISO
100 - 12800. Under [z3: ISO speed settings], if you set [ISO
speed range]'s [Maximum] setting to [25600/H], the maximum ISO
speed will be expanded and the ISO speed will be set automatically
within ISO 100 to H.
You can set the ISO speed manually within ISO 100 - 12800 in 1/3-stop
increments. Under [z3: ISO speed settings], if you set [ISO speed
range]'s [Maximum] setting to [25600/H], the maximum ISO speed for
manual ISO speed setting will be expanded to H (equivalent to ISO
25600). Be aware that when you set [Maximum] to [25600], the
maximum ISO speed will not be expanded and remains ISO 12800.
If [z4: Highlight tone priority] is set to [Enable] (p.130), you can
set the ISO speed within ISO 200 - 12800 (depending on the [ISO
speed range] setting).
Under [z3: ISO speed settings], [Auto ISO range] or [Min.
shutter spd.] cannot be set (p.110, 111) for movie shooting.
Since shooting a movie at ISO 16000/20000/25600 may result in much
noise, it is designated as an expanded ISO speed (displayed as [H]).
If [Minimum] is set to [L (50)] and [Maximum] to [H1 (51200)] or [H2
(102400)] in [ISO speed range], and you switch from still photo shooting
to movie shooting, the minimum setting for manual ISO range will be ISO
100 and the maximum will be H (ISO 25600). The ISO speed cannot be
expanded to ISO 50 or ISO 51200/102400.
Changing the shutter speed or aperture during movie shooting is not
recommended since the changes in the exposure will be recorded.
When shooting a movie of a moving subject, a shutter speed of 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
lighting, image flicker may be recorded.
When ISO Auto is set, you can press the <A> button to lock the ISO speed.
If you press the <A> button and recompose the shot, you can see the
exposure level difference on the exposure level indicator (p.22, 210)
compared to when the <A> button was pressed.
By pressing the <B> button, you can display the histogram.
k Shooting Movies
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