The Role of ISO in Digital Photography?

The best way to learn things like photography. Nobody can teach you photography - you have to discover it! For maths and science, maybe not so much. ;-)

I am not sure if the OP wanted to learn or wanted to teach.

I am not sure if the OP wanted to learn or wanted to teach.

Regardless of which it is, photography can and has been both learned and taught since its inception.

Nobody can teach you photography

A lot of teaching and learning goes on in the various forums on PN, in photo classes and photo clubs at all levels all over the place.

I find learning from others who are good teachers incredibly valuable. I find it's also up to me to have a core strong enough to put that learning to my own individual use and adapt it to my vision rather than adopting the vision of anyone from whom I learn.

Regardless of which it is, photography can and has been both learned and taught since its inception.

 

A lot of teaching and learning goes on in the various forums on PN, in photo classes and photo clubs at all levels all over the place.

 

I find learning from others who are good teachers incredibly valuable. I find it's also up to me to have a core strong enough to put that learning to my own individual use and adapt it to my vision rather than adopting the vision of anyone from whom I learn.

I was responding to Karim who advised the OP on the learning process. However, I feel the OP tried to teach us something rather than trying to learn.

I was responding to Karim who advised the OP on the learning process. However, I feel the OP tried to teach us something rather than trying to learn.

Yes, my comments were really in response to Karim. Sorry for being unclear about that. As for the OP and teaching and learning, a good learner can teach. A good teacher will also learn from his student(s).

But in all this I got to wondering how important ISO is in digital photography and why in the world a camera's ISO capabilities would go so high as 23,000? How does digital ISO relate to actual film speeds and stuff? Is or was there ever a film with a super high ISO? If not, why then, these (what seem like) crazy levels of ISO in digital?

I don't know if you ask a question or making a statement but my answer to these are.

1. Why in the world a camera's ISO capabilities would go so high as 23000? Because you need it and more which proven in the case of the race. You need even higher ISO to get good pictures in that race.

2. While digital sensor has only 1 sensitivity the ISO just boost the signal up but you can consider them equivalent to that of film ISO for the start.

3. There wasn't a film with super high ISO. I only know of ISO3200 film. But why? Because they couldn't make super high speed film. As Joe demonstrated at 3200 it's terrible. But what you can't make doesn't mean you don't need or want it. In fact you needed it for the race pictures.

why in the world a camera's ISO capabilities would go so high as 23,000?

Why would you question the marvels that modern technology can offer us?

40 years ago, there was many a professional photographer and photojournalist that would have sold their soul for a film with a true ASA rating anywhere near 23000. Or even a real rating of 3200 that didn't have grain like golf balls. Amateurs too I suppose. Nowadays, most photographers don't give a second thought to winding the ISO up to 1600 or 3200 - and expecting relatively noise-free results. That's progress. Why question its worth?

TMax 3200 and Delta 3200 have development times for up to 25000.

https://imaging.kodakalaris.com/sites/prod/files/files/products/f4001_tmax_3200.pdf

I haven't tried it yet, but I hope to do so soon.

They have different structure, but grain is basically a form of noise.

Instead of a uniform gray, you get a combination of black (grains) and white (space between them)

that averages out to the appropriate gray level. At higher ISO values the grains are larger, and

there are fewer of them for a give gray level.

Note that the fundamental limitation in both film and digital is the quantum nature of light.

You only get whole photons, never partial ones.

In the digital case, a specific number of photons hit a photodiode, each one generating a

photoelectron (and photohole). Poisson statistics tells us that, for a given expected number

of photons, n, that actual measured value will have an uncertainty (standard deviation)

of the square root of n. This is fundamental to anything that depends on a count of otherwise

random events. (This also applies to coin flips and dice rolls.)

In addition, there is thermal noise. First, even with no photons, you still get some

electron-hole pairs. But also due to the quantum nature of electrons, there will

be a voltage across a resistor, even with no current, proportional to the square

root of temperature. This is explained here:

Johnson–Nyquist noise - Wikipedia

This noise exists in all electronic amplifiers.

There are significant differences between the way grain noise appears

in film, and noise appears in digital images, but you can partly ignore

this difference. Higher ISO values give more noise in both film and

digital. Lower ISO is lower noise in both cases.

Glen, WOW!

OK that's taking it to levels I could not have imagined. The science of photography aka capturing light. Thanks.

Why would you question the marvels that modern technology can offer us?

 

40 years ago, there was many a professional photographer and photojournalist that would have sold their soul for a film with a true ASA rating anywhere near 23000. Or even a real rating of 3200 that didn't have grain like golf balls. Amateurs too I suppose. Nowadays, most photographers don't give a second thought to winding the ISO up to 1600 or 3200 - and expecting relatively noise-free results. That's progress. Why question its worth?

Because I must? Is it ignorance or arrogance? Not knowing, I question even my own questions.

I am not sure if the OP wanted to learn or wanted to teach.

Oh, to learn, please & thank you.

If I can see further than other men, it's because I stand on the shoulders of giants. Sir Isaac Newton

I am humbled, sir. Thank you.

........a good learner can teach. A good teacher will also learn from his student(s).

Opportunities for learning can be found even in the most unlikely of places. But first, one must be open to them.

I find learning from others who are good teachers incredibly valuable. I find it's also up to me to have a core strong enough to put that learning to my own individual use and adapt it to my vision rather than adopting the vision of anyone from whom I learn.

Thank you, Sam!

This conversation is very informative indeed. Thanks very much to all participants for your valuable insights and knowledge. I really appreciate it.

I'm going to try to reassemble a few of the pieces of this thread because I think it might lead you to misunderstand a key point.

 

This may sound like nitpicking, but it isn't: increasing ISO does not increase the camera's sensitivity to light. Given any exposure to light, the signal recorded by your sensor is fixed. Increasing ISO only increases the degree to which that signal is amplified. It's a way of compensating for having less light. It is NOT analogous to putting a faster film into a film camera. It's more like pushing a film above its native ISO in developing, although actual process of boosting, the the impact it has on the image, are different.

 

Increasing ISO has its costs. Many modern sensors can handle increases in ISO much better than sensor did in the past, so the costs are smaller, but they are there. One is that increasing ISO will give you more noise than a similar exposure at a lower ISO (that is, an exposure that produces an image of the same brightness), for the simple reason that it amplifies everything, signal as well as noise. This extra noise can be inconsequential, particularly if you don't go to high and if you don't have much in the way of very dark shadows, but it can be severe. The second effect, which is really another expression of the first, is that increasing ISO decreases dynamic range--that is, the range from the darkest to the lightest tones the camera can record.

 

There are reasons to accept these costs. You may need to because of low light. You may do it to allow you to use a faster shutter speed or narrower aperture. If you are using TTL flash, you may do this to increase the brightness of the background relative to the target. However, many people, including me, keep the ISO as low as we can.

 

How big the costs are depend on the camera's sensor and the type of image. For example, I shoot with both a 5D III and a 7D I, and the noise caused by increasing ISO is substantially less with the 5D III. The brighter an image is, the less the impact because the signal:noise ratio is higher in bright areas.

It sounds about the same as film when you look at the end results. Bigger film grain = more sensitive to light = bigger grain in the finished photo.

I'm with you, try to keep ISO as low as I can while balancing aperture and shutter speed.

My thoughts, as someone who has only recently made the switch from film to digital.

Try setting your aperture and shutter to manual, but the ISO to auto. Essentially this is giving you a third auto-exposure mode, where aperture and shutter speed are locked to your settings and ISO floats to control exposure. The ability to do this varies by camera, but some will then allow you to bias the camera's chosen exposure using the EV comp, just as you would in 'A' or 'S'. Depending on how you shoot, this might be nothing, or it might be a revelation, giving you control over the third side of the exposure triangle. I'm still getting to grips with it, but I'm finding it very useful.

Alternately, it also pays to remember that digital sensors only really have one (or two, in the case of dual-gain designs) 'real' ISO sensitivity, everything else is effectively a push or pull operation, with resulting loss of dynamic range. So best results will always be obtained by correctly exposing at the sensor's base ISO, if conditions allow.

TMax 3200 and Delta 3200 have development times for up to 25000.

No, they have development times that increase their contrast enormously. The speed-point of the film stays firmly rooted to the X axis of their H&D curve at around -3 log lux-seconds, or a true 1250 ISO. And the grain stays stubbornly golf-ball sized.

All the quoting of physics in the world doesn't change that. Nor the fact that electronic sensors are far more photon efficient than chemical capture and amplification is ever likely to be.

So best results will always be obtained by correctly exposing at the sensor's base ISO..

But the ISO definition of a digital sensor's base ISO is basically 'that speed setting which gives the best image quality'. It's kind of a self-fulfilling prophesy, or a catch 22 situation (as well as being a copout by the ISO for not defining a separate and rigid methodology for digital sensor speed determination, and simply giving speed parity with that of an equivalent film). It also ignores the fact that area-for-area the IQ delivered by a digital sensor is far superior to that of film.

The fact remains that raising the ISO speed of a digital camera truly reveals more shadow detail. Whereas 'pushing' (simply over developing) film genuinely does not.

Also, the noise penalty, again in an area-for-area comparison, is undeniably less for a digital sensor, than it is for film.

No, they have development times that increase their contrast enormously. The speed-point of the film stays firmly rooted to the X axis of their H&D curve at around -3 log lux-seconds, or a true 1250 ISO. And the grain stays stubbornly golf-ball sized.

 

All the quoting of physics in the world doesn't change that. Nor the fact that electronic sensors are far more photon efficient than chemical capture and amplification is ever likely to be.

They have times for up to EI 25000.

The meaning of those times and EI values are open to interpretation, and as you note

increased contrast is one effect.

The data sheet is here:

https://www.ilfordphoto.com/amfile/file/download/file/1913/product/683/

Looking at it more carefully than I did before, yes the contrast goes up.

But at the ISO rated 1250, the gamma is only about 0.5, so it can go up some

without being so high.

At EI 25000, it looks like about 0.8, so not so high as you might have thought.

About gamma 0.65 at the suggested 3200.

What Ilford actually says is:

"It can be exposed at ratings up to EI 25000/45, but it is important to make test exposures

first to ensure the results will be suitable for the intended purpose."

Many low-light scenes have fairly low contrast to start, so some increase might help.

My thoughts, as someone who has only recently made the switch from film to digital.

 

Try setting your aperture and shutter to manual, but the ISO to auto. Essentially this is giving you a third auto-exposure mode, where aperture and shutter speed are locked to your settings and ISO floats to control exposure. The ability to do this varies by camera, but some will then allow you to bias the camera's chosen exposure using the EV comp, just as you would in 'A' or 'S'. Depending on how you shoot, this might be nothing, or it might be a revelation, giving you control over the third side of the exposure triangle. I'm still getting to grips with it, but I'm finding it very useful.

 

 

Alternately, it also pays to remember that digital sensors only really have one (or two, in the case of dual-gain designs) 'real' ISO sensitivity, everything else is effectively a push or pull operation, with resulting loss of dynamic range. So best results will always be obtained by correctly exposing at the sensor's base ISO, if conditions allow.

Steve, thank you this seems like helpful information and a good place to start. For a lark, I'm going to try something I've never done- reading the manual! I'll have some downtime this weekend and will be shooting a load of film and digital so I'm going to bone up on my camera's manual settings.

Thanks again to everyone for your wisdom, experience, and input.