Canon EOS M EF-M 22mm STM Kit Instruction Manual page 111

ISO Speed Guide
ISO Speed
100 - 400
400 - 1600
1600 - 12800, H
* High ISO speeds will result in grainier images.
Under [54: Custom Functions (C.Fn)], if [2: ISO expansion] is set to
[1: On], "H" (equivalent to ISO 25600) can also be set (p.284).
Even if a low ISO speed is set, noise may be noticeable in the LCD
monitor image under low light. However, when you shoot, the image
recorded will have minimal noise. (The image quality of the LCD monitor
image is different from that of the recorded image.)
Under [54: Custom Functions (C.Fn)], if [3: Highlight tone priority] is
set to [1: Enable], ISO 100 and "H" (equivalent to ISO 25600) cannot be selected (p.285).
Shooting in high temperatures may result in images that look grainier.
Long exposures can also cause irregular colors in the image.
When you shoot at high ISO speeds, noise (such as dots of light and
banding) may become noticeable.
If you use a high ISO speed and flash to shoot a close subject, overexposure may result.
With ISO 12800 or "H" (equivalent to ISO 25600), the number of possible
shots/maximum burst for continuous shooting will greatly decrease.
As "H" (equivalent to ISO 25600) is an expanded ISO speed setting,
noise (such as dots of light and banding) and irregular colors will be more
noticeable, and the resolution will be lower than usual.
As the maximum ISO speed that can be set differs between still photo shooting
and movie shooting (manual exposure), the ISO speed you set may change
when you switch from still photo shooting to movie shooting. Even if you switch
back to still photo shooting, the ISO speed will not revert to the original setting.
The maximum ISO speed that can be set varies depending on the setting
for [2: ISO expansion] under [54: Custom Functions (C.Fn)].
• When [0: Off] is set: If you set ISO 12800 during still photo shooting and
then switch to movie shooting, ISO speed will be changed to ISO 6400.
• When [1: On] is set: If you set ISO 12800/H (equivalent to ISO 25600)
during still photo shooting and then switch to movie shooting, ISO
speed will be changed to "H" (equivalent to ISO 12800).
Shooting Situation (No flash)
Sunny outdoors
Overcast skies or evening time
Dark indoors or night
3 i: Changing the ISO SpeedN
Flash Range
The higher the ISO speed,
the farther the flash range
will extend (p.139).
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