ISO 100, OMD-EM1II and firmware 3.0?

Started 2 months ago | Questions thread
Chris Noble
Chris Noble Veteran Member • Posts: 3,143
Re: Meaning of base vs. extended ISO

bobn2 wrote:

katastrofa wrote:

My photos look more noisy when I increase the ISO. Why?

Changing the ISO sets the meter so that you choose to use a lower exposure. Lower exposure means less light energy. Less light energy means fewer photons captured in the image. The signal to noise ratio in the image goes as the square root of the number of photons, so if you capture fewer, you get a lower SNR, which you say is 'more noisy'.

You are mixing changes in exposure vs. changes in ISO setting.

Katastrofa's observation is correct even if the exposure does not change (using manual metering for example). The ISO gain introduces additional noise on top of the exposure noise.

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