Nikon D100 - Manual (Page 160)

Custom Settings
Menu Guide—Custom Settings
148
Custom Setting 3: ISO Auto
If ON is selected for this option, the camera will
automatically adjust sensitivity (ISO equivalency)
when optimal exposure can not be achieved at
current exposure settings. If sensitivity is set to
HI-1 (approximately equivalent to ISO 3200) or
HI-2 (approximately equivalent to ISO 6400), this
option is automatically set to OFF and can not
be adjusted.
OK
ISO Auto Control F3
CSM MENU
OFF
ON OFF
ON
Bank Select
If a shooting menu bank in which ISO has been set to or is chosen after ON
is selected for Custom Setting 3 (ISO Auto), sensitivity (ISO equivalency) will
NOT
be
adjusted automatically. Sensitivity will also not be adjusted automatically if a Custom
Settings bank in which ON is selected for Custom Setting 3 (ISO Auto) is chosen after
ISO has been set to
or .
ISO Auto
If a Speedlight is used when ISO Auto is on, sensitivity (ISO equivalency) will be fixed at
the value selected by the user.
Noise
Noise is more likely to appear in photographs taken at higher sensitivities.
Option Description
OFF
(default)
Sensitivity remains fixed at value selected by user, regardless of
whether optimal exposure can be achieved at current exposure
settings.
ON
When optimal exposure can not be achieved at the sensitivity
selected by the user, sensitivity is adjusted to compensate, to a
minimum approximately equivalent to ISO 200 and a maximum
approximately equivalent to ISO 1600 (
76). Sensitivity can
not be set to HI-1 or HI-2 while this option is in effect.