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Can someone explain how ISO/Base ISO functions these days? (alien.top)

submitted 11 months ago by Spirit-Subject@alien.top to c/photography@viewfinder.pro

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So generally, I’ve always understood that the lowest ISO is best to shoot at. Though with newer cameras, they usually have a higher base ISO and in some cases Dual ISO.

I usually work with the R5C, even for photography. It feels odd to take portraits at 800 ISO because I’ve always been told it should be as low as possible.

So does the Base ISO system, negate the need to shoot at lowest ISO for the clearest and least grainy image?

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[–] oldlurker114@alien.top 1 points 11 months ago

Pretty much right, though I'll clarify a bit if I may:

Seeing more noise at higher ISOs is because light noise is related to the square root of the number of photons

Noise is related to the number of photons. What the square root gives is the standard deviation (due to the Poisson distribution that light particles follow) and "noise" is the signal to noise ratio, SNR, the ratio of the number of photons to the standard deviation. And this is of course funnily also the square root of the number of photons.

A lower number has a relatively higher square root. Less light has relatively higher noise

I do understand what you mean, but this is IMHO rather confusingly put and especially for beginners impossible to comprehend what you mean.

Simply, more light means larger SNR. The standard deviation of the signal goes up, but the signal itself goes up much more. What an observer sees as "noise" is simply a product of low SNR.

The base ISO is the one where the sensor system is designed to have the highest signal to noise ratio at the “correct” exposure.

The image sensor has no ISO at all. It can be run at different parameters and typically changing the camera's ISO setting changes there operational parameters.

The concept of "base ISO" isn't officially defined (by ISO, the organization) and can interpreted in many ways. If we go by your definition above, then it would be typically the lowest extended ISO setting as the exposures are typically larger than the ones with the lowest "regular ISO" settings. Many people on the other hand seem to consider the lowest "regular ISO" to be the "base ISO". FWIW, usually the image sensor is driven with the same parameters in both cases.

ISO value itself is really a property of output formats, like JPG.

IMHO the concept of base ISO should be abolished for above reasons. It's likely more harmful than useful for beginners.