How does the Auto ISO sensitivity control work?

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abhijitsarkar
abhijitsarkar Regular Member • Posts: 284
How does the Auto ISO sensitivity control work?

With the auto ISO sensitivity turned on, and a minimum shutter speed set to 1/125, I'd expect the camera to simply default to ISO 100 (camera minimum) when the shutter speed is above the minimum. Otherwise, it'd raise the ISO incrementally until the minimum shutter speed is reached.

However, I'm not seeing the D780 work this way. In aperture priority mode, and aperture = f/8, it chose a shutter speed of 1/8000 and ISO 3200, whereas it could've chosen an equivalent setting of ISO 100 and 1/250 shutter speed for a much cleaner image. Can anyone explain this behavior to me?

Relevant section from the manual:

https://onlinemanual.nikonimglib.com/d780/en/06_shooting_settings_06.html#CHEJCFBAF0

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