Auto Iso - Nikon D300 Complete Manual

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better than the camera, in my opinion. See my

recommendations in Introduction to Nikon Software.

Auto ISO

The ISO sensitivity auto control option tends to be

misunderstood by virtually all users; it does not operate quite

as you'd expect and has definite limitations. Fortunately, the

D300's high ISO capabilities are good enough that this is a

useful option.

Previous Nikon DSLRs used a Custom Setting to enable

automatic ISO and set its options. The D300 and D3 have

moved this to sub-menus on the SHOOTING menu (ISO

sensitivity settings).

What happens when ISO sensitivity auto control is set to

On depends upon what exposure mode you're using:

In Manual exposure mode, the ISO is changed if the

shutter speed and aperture combination you pick won't

achieve a proper exposure (manual exposure bar centered

at 0: ó). For example, if you were at ISO 200 and set f/8

at 1/125 but the meter thought the exposure should be

f/5.6 at 1/125, the camera will boost the ISO one stop to

400 (f/8 is one stop underexposed compared to f/5.6 in

this example).

In Shutter-priority exposure mode, the ISO is changed

when the camera runs out of aperture range to use. For

instance, assume that the initial ISO value is 200 and the

aperture is set by the camera to the lens' maximum of

f/2.8. If the lighting changes such that f/2 is required, the

ISO will be boosted one stop to 400 (f/2.8 is one stop

underexposed compared to f/2 in this example).

In Program and Aperture-priority exposure modes, ISO

isn't changed until the exposure reaches the extreme at

either end of the shutter speed range (1/30 second at the

bottom end unless you set a different value with

Minimum shutter speed); the upper limit is always

Thom Hogan's Complete Guide to the Nikon D300