Canon EOS R6 Mark II Mirrorless Camera with 24-105mm f/4-7.1 Lens - Manual (Page 184)

ISO speed guide
Low ISO speeds reduce image noise but may increase the risk of camera/subject shake
or reduce the area in focus (shallower depth of field), in some shooting conditions.
High ISO speeds enable low-light shooting, a larger area in focus (deeper depth of field),
and longer flash range but may increase image noise.
Note
ISO speed can also be set in the ISO speed item by pressing the < > button
with an image displayed on the screen.
To expand the manual ISO speed setting range from L (equivalent to ISO 50) to H
(equivalent to ISO 204800), adjust [
ISO speed range ] in [ : ISO speed
settings ] ( ).
Caution
Image noise (dots of light or banding) and irregular colors may increase and
apparent resolution may decrease at H (equivalent to ISO 204800), because this is
an expanded ISO speed.
Because L (equivalent to ISO 50) is an expanded ISO speed setting, the dynamic
range will be somewhat narrower compared to the standard setting.
Setting [
: Highlight tone priority ] to [ Enable ] or [ Enhanced ] ( ) will prevent
you from selecting L (equivalent to ISO 50), ISO 100/125/160, or H (equivalent to
ISO 204800).
When shooting with a high ISO speed, high temperature, long exposure, or multiple
exposure, image noise (graininess, dots of light, banding, etc.), irregular colors, or
color shift may become noticeable.
When shooting in conditions that produce an extreme amount of noise, such as a
combination of high ISO speed, high temperature, and long exposure, images may
not be recorded properly.
If you use a high ISO speed and flash to shoot a close subject, overexposure may
result.
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