ISO Invariance and Noise Explanation

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Velmahr Regular Member • Posts: 128
ISO Invariance and Noise Explanation

So I've been reading about ISO invariance, but I just want to make sure I'm getting it right.  Basically, when a camera takes a picture, photons from the subject land on the sensor, where it goes through an amplifier, then through a converter that transforms the analog signal to a digital signal.  If the camera is ISO variant, then the converter's noise overpowers the signal if not enough amplification is provided, so if I underexposed an ISO 100 shot by 5 stops, the weak signal wouldn't have enough amplification to overpower the noise caused by the converter.  At ISO 3200, the amplified signal wouldn't be affected by the weak, but present, noise caused by the converter.

On an ISO invariant camera the noise caused by the converter is so low that it doesn't make a difference whether the signal is weak to begin with, so underexposing shots by lowering ISO as much as possible would preserve tonal range and color.

Am I right in my explanation?  Am I using the right terms?  I'm creating a video about ISO-invariance, so I want to be as correct as possible, and use the correct terms.

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