Are there any "rules" for using ISO?

Started Apr 3, 2013 | Discussions thread
baloo_buc Veteran Member • Posts: 9,472
Re: Are there any "rules" for using ISO?

There is certainly a rule:

Increase the ISO when other means of adjustment (shutter speed and aperture) could not be used anymore.

In most cases you can set the aperture as wide as possible and the shutter speed as high as needed and then increase the ISO speed.

If you use Nikon you have a powerful tool in ISO Auto. You either use A mode and set the aperture while setting the shutter speed via the ISO Auto (the soft way) or use the M mode and set both the aperture and shutter speed and let ISO Auto to manage the exposure (the hard way).

In the A mode if the max ISO is reached then the shutter speed is modified downwards.

In the M mode if the max ISO is reached then underexposure occurs and when the minimum ISO is reached overexposure occurs.

Let's say you have as light ISO200, f/5.6 and 1/320 s. The ISO Auto is set at shutter speed of 1/640 s and max ISO Speed at ISO3200. Your current ISO is ISO200, which is the minimum ISO setting also for ISO Auto.

In A mode you set f/8. Then the camera will use ISO Auto and set the shutter speed at 1/640 s and the ISO Speed at ISO800.

In M mode if you set f/8 and 1/500 s then the ISO Auto will set ISO640.

If the light is ISO200, f/5.6 and 1/20 s there is another situation:

A mode f/8 (set by you), 1/160 s (set by ISO Auto) and ISO 3200 (set by ISO Auto).

M mode f/8 (set by you), 1/500 s (set by you) and ISO 3200 (set by ISO Auto). In this case underexposure occurs (1,7 EV).

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