Canon EOS 90D DSLR Camera with 18-135mm Lens - Manual (Page 214)

214
ISO Speed Settings for Still Photos
o Image noise (such as dots of light or banding) may increase and apparent
resolution may decrease at H (equivalent to ISO 51200), because this is an
expanded ISO speed.
o ISO 100/125/160 or an expanded ISO speed cannot be selected when
[
z
: Highlight tone priority] is set to [Enable] or [Enhanced] ( = 219).
o When shooting with a high ISO speed, high temperature, long exposure, or
multiple exposure, image noise (rough grain, dots of light, banding, etc.),
irregular colors, or color shift may become noticeable.
o 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.
o If you use a high ISO speed and fl ash to shoot a close subject, overexposure
may result.