The role shutter speed has to flash photography.

[Manfred M]

May I clarify that?

Only the shutter speed and aperture directly impact the exposure of the sensor. All other forms of chicanery such as, ISO, EC, etc., affect only the combination of shutter speed and aperture, therefore ISO affects exposure indirectly.

The proof of the pudding being in that, if one sets the camera in manual at some fixed combination of shutter speed+aperture and then waggles the ISO knob around taking many shots of the same scene, the raw data (i.e. sensor exposure) will not change much, if at all.

While this is admittedly a trivial clarification and could be viewed as irrelevant, it may have some bearing on this thread's discussion.

If you take a sensor-centric view, I can see where you are coming from, but photographers don't use this plane of reference.

We use the output of our camera as our reference. Replace the sensor with traditional film, and ISO is indeed relevant as we are not dealing with a device with a fixed ISO where adjusting the gain emulates what changes in film ISO do.

[xpatUSA]

If you take a sensor-centric view, I can see where you are coming from, but photographers don't use this plane of reference.

Nor does CiC, apparently:

"ISO speed: controls the sensitivity of your camera's sensor to a given amount of light" . .

https://www.cambridgeincolour.com/tu...a-exposure.htm

Certainly an output-referred view, and it's just plain wrong because the sensitivity of most cameras' sensor to a given amount of light remains constant irrespective of the ISO setting (expect for those odd sensors with dual-diode pixels or switchable capacitors).

Please pardon the late edit but, once again, I am bothered by terminology. I get an impression that someone who uses a "sensor-centric" "plane of reference" is not a photographer. Not that I am claiming to be one, BTW.

We use the output of our camera as our reference. Replace the sensor with traditional film, and ISO is indeed relevant as we are not dealing with a device with a fixed ISO where adjusting the gain emulates what changes in film ISO do.

Yes, I wasn't disagreeing, just clarifying.

So, when CiC says "exposure", it actually means "image brightness" like as here:

https://www.nayuki.io/page/the-photo...osure-equation

Whereas, in the film days, "exposure" meant something else.

Got it now though, thanks for the clarification of my clarification . .

P.S. It's a bit like two of the ISO 22232 methods of determining a camera's Exposure Index:

Saturation-based for both film and digital requiring knowledge of film or sensor saturation exposure in lux-seconds . .

or Standard Output Sensitivity which requires repeating shots until the sRGB output gives 118/255 for an 8-bit image.