Nikon D40 - Manual (Page 88)

76 Menu Guide/Custom Settings
8: Flash Level (P, S, A, and M Modes Only)
Adjust flash level ( 48).
9: AF-assist (All Modes Except and )
If On (the default setting) is selected and the subject is poorly lit,
the AF-assist illuminator will light to assist the focus operation in
single-servo AF (AF-S or single-servo AF selected in AF-A autofocus
mode). Choose Off to disable the AF-assist illuminator. Note that
when the illuminator is off, the camera may not be able to focus
on poorly-lit subjects using autofocus.
10: ISO Auto (P, S, A, and M Modes Only)
If Off (the default setting) is selected, ISO sensitivity will remain
fixed at the value selected by the user ( 37). If On is selected,
ISO sensitivity will automatically be adjusted if optimal exposure
can not be achieved at the selected value (flash level is adjusted
appropriately). The maximum value for auto ISO sensitivity can be
selected using the Max. sensitivity option. In modes P and A,
sensitivity will only be adjusted if underexposure would result at the shutter speed selected
for Min. shutter speed (slower shutter speeds may be used if optimal exposure can not be
achieved at the value selected for maximum sensitivity).
When On is selected, the viewfinder and shooting information
display show ISO-AUTO. Unless a flash is used, these indicators blink
when sensitivity is altered from the value selected by the user.
Note that noise is more likely at higher sensitivities.
ISO Auto
Auto ISO control is not available at an ISO sensitivity of HI 1. Foreground subjects may be
underexposed in photos taken with the flash at slow shutter speeds, in daylight, or against a bright
background. Choose a flash mode other than slow sync or select mode A or M and choose a larger
aperture.