Ever increasing ISO range

[fatmarley]

But on a slightly serious note, all sensors do is capture and count photons, and so logically there must be a physical limit where every single available photon is being captured and counted. I've been trying to work out where that limit is - i.e. what ISO value it would equate to. I suspect it's some way short of 6,000,000 for the kinds of pixel densities we're used to - but it's proving to be surprisingly difficult to work out. Does anyone know of this exercise having been performed? Or can anyone point to a good reference about photons, quantum efficiency of sensors, and such like?

What usually happens is someone looks at the problem from a different angle and find a way around it.

 

[insomniac]

The dynamic range of my other balls has also reduced over the years.

You do know that you can seek pharmaceutical assistance for that particular ailment, right?

 

[Terrywoodenpic]

At our camera club a few weeks ago we had a talk entitled "Art, craft and technology" where the speaker looked at technological developments in the photographic area and how they impacted on what photographers actually do. For example the large capacity of memory cards compared to film has revolutionised underwater photography, and the high ISO capabilities of modern DSLRs allow photographers to capture images which simply wouldn't be possible on film.

He also extrapolated from current trends and predicted that, within 9 years, we'll have DSLRs offering a maximum ISO of 6,000,000 and 16 stops of dynamic range.

I disagreed that it would go that far, and I have a date in my diary for September 2022 when beer will be bought depending on who turns out to be right.

But on a slightly serious note, all sensors do is capture and count photons, and so logically there must be a physical limit where every single available photon is being captured and counted. I've been trying to work out where that limit is - i.e. what ISO value it would equate to. I suspect it's some way short of 6,000,000 for the kinds of pixel densities we're used to - but it's proving to be surprisingly difficult to work out. Does anyone know of this exercise having been performed? Or can anyone point to a good reference about photons, quantum efficiency of sensors, and such like?

You are quite right of course, sensors are already sensitive enough to count all the Photons available even by moon light at reasonable apertures and shutter speeds...
Increasing the sensitivity further can add nothing, as no photons remains no photons.
At best, you can just increase the time the shutter is open, and wait for a few more photons to arrive. But you can do that at any sensitivity.

 

[sk66]

ISO of a film stock is a measure of how reactive to light a chemical emulsion is.

ISO in digital is made up. It sets the gain of the CMOS amplifier. Higher gain, higher noise figure, worse signal to noise ratio. To go lower in fake ISO, you'd need to attenuate the signal. You can't do it the old fashioned way as resistors are a bad idea in CMOS.

I agree with this.
A camera only has one ISO; all others are achieved by "pushing/pulling" the ISO very much like it was done with film. The other "real" ISO's are achieved by signal manipulation (amplification) but it is not a change to what is actually collected. The "extended" ISO's are achieved by digital manipulation after conversion, but prior to recording to disk/card.

All of the rated/reported sensor characteristics (bit depth, dr, etc) only occur at the native ISO with full saturation. Anything else and you are loosing something. Many of the "gains" in ISO performance are due to more advanced processing; a raw file is not "raw," a card does not record/store electrons. Or it's due to "oversampling;" using larger numbers of pixels to produce images.

The problem with lower base ISO is it results in a "tripod only" camera because the penalties of amplification/processing due to not fully saturating the sensor are exponential. Could they do it? I'm sure they could, but relatively few would want it.
In a related sense, lower base ISO's also reduce the power/effectiveness of lighting equipment.