A reminder for some memebers as to what the F stop is all about.

Started Jan 26, 2014 | Discussions thread
bobn2 Forum Pro • Posts: 62,183
Re: And the answer is:

DonSC wrote:

No idea really. For me "same ISO" is just a shorthand for same shutter speed and aperture.

I think most people think that way, but it really depends on how the particular camera meters.

I've always assumed that for different ISO the electronics are optimized for different amounts of light.

Changing the ISO setting applies either an analog or digital amplification to the signal.  In the case of analog amplification with non-ISOless sensors, this results in less read noise.  That's why, for example, a photo at f/2.8 1/200 ISO 3200 will look less noisy than a photo of the same scene at f/2.8 1/200 ISO 100 pushed 5 stops in the conversion.  On the other hand, if the amplification is digital, then the two photos would look the same.

But the ISO exposure index standards don't specify at all how much 'amplification' should be applied. So how can 'ISO' be about amplification?

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