Exposure and ISO

[250swb]

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4 hours ago, SrMi said:

That is true, but that has nothing to do with the correct definition of exposure. One can adjust exposure in many ways; some are manual, others are automatic.

There are many expressions in photography that don’t match the technical definition, but we all know what they mean, as in the extended metaphor of the Ai Shakespeare previously demonstrated to you.
 

Terms such as ‘take’, ‘capture’, ‘shoot’, ‘snap’, ‘shot’, ‘grab’, or even ‘make’ have no technical meaning other than we know what they mean. It is a unique feature of the English language that metaphor and meaning are often interchangeable in a discussion. So if somebody said in the context of ‘shooting’ a sporting event they set the aperture and set the required shutter speed, and then put the ISO on Auto to determine the exposure I would know they mean they set the ISO not to ‘exposure’ but to ‘sensitivity’, but I wouldn’t normally be bothered to argue the point because we all know what was meant. Which leaves the question of how much value is there in insisting on a ‘technical’ discussion if you’ve ever even casually used non- technical words to describe photography? Are you making the point that in all of your discussions you never use metaphor to represent meaning?

[SrMi]

38 minutes ago, 250swb said:

There are many expressions in photography that don’t match the technical definition, but we all know what they mean, as in the extended metaphor of the Ai Shakespeare previously demonstrated to you.
 

Terms such as ‘take’, ‘capture’, ‘shoot’, ‘snap’, ‘shot’, ‘grab’, or even ‘make’ have no technical meaning other than we know what they mean. It is a unique feature of the English language that metaphor and meaning are often interchangeable in a discussion. So if somebody said in the context of ‘shooting’ a sporting event they set the aperture and set the required shutter speed, and then put the ISO on Auto to determine the exposure I would know they mean they set the ISO not to ‘exposure’ but to ‘sensitivity’, but I wouldn’t normally be bothered to argue the point because we all know what was meant. Which leaves the question of how much value is there in insisting on a ‘technical’ discussion if you’ve ever even casually used non- technical words to describe photography? Are you making the point that in all of your discussions you never use metaphor to represent meaning?

There is a difference whether we are having a technical discussion, when precision of terms is more important, and colloquial and jovial discussion, when everything goes.

[LocalHero1953]

There is also a difference between someone's definition and the actual usage common and current among photographers. (This applies to words in general, of course, not just photography words).

We got along just fine until Dr Johnson and his dictionary.

[pgk]

1 hour ago, LocalHero1953 said:

There is also a difference between someone's definition and the actual usage common and current among photographers

Whilst true this doesn't make the incorrect usage of terminology right.

To be pedantic, exposure relates to the process of allowing light to fall on a sensitive surface. How this is controlled is not defined by the word itself.

[LocalHero1953]

To those choosing to be pedants, please give an authoritative source for a definition of 'exposure'.

I have tried ChatGPT, Gemini, and simple google search, and most results are ambiguous at best. So suggesting that we should be as strict in our usage as some would like us to be will simply not help with normal communication.

Edited yesterday at 12:14 PM by LocalHero1953

[SrMi]

7 hours ago, LocalHero1953 said:

There is also a difference between someone's definition and the actual usage common and current among photographers. (This applies to words in general, of course, not just photography words).

The famous quote from Princess Bride always comes to mind: "You keep using that word. I do not think it means what you think it means."  🤣

[pgk]

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3 hours ago, LocalHero1953 said:

To those choosing to be pedants, please give an authoritative source for a definition of 'exposure'.

Wiki says it quite well for us pedants: https://en.wikipedia.org/wiki/Exposure_(photography)

However, I would suggest that in its simplist form the word has always been used in photographic contexts meaning when light sensitive material is exposed to light. This is exactly what I have always understood photographic exposure to be (eg. an exposed film is a film which has had light fall upon it). It is independant of the mechanisms used to do this. An 'exposure' is therefore the act of exposing light sensitive material to light.

After this we can discuss topics such as the mechanisms designed to expose light sensitive materials to a specific amount of light and carry on from there, and digital has undoubtedly shifted the mechanism of exposure away from its traditionally understood meaning, subtly if no more (there is no latent image). But exposure simply referes to exposing light sensitive material to light, nothing more, nothing less. 

[SrMi]

4 hours ago, LocalHero1953 said:

To those choosing to be pedants, please give an authoritative source for a definition of 'exposure'.

Both the Wiki and the ISO standard (buried somewhere) specify exposure as the amount of light per unit area that reaches the sensor.

Of course, I could also list numerous individuals recognized as authorities in the field of photographic science and technology.

P.S.: The ISO standard is ISO 12232:2019.

Edited yesterday at 04:16 PM by SrMi

[LocalHero1953]

I doubt many photographers would choose to read the wikipedia entry on exposure as a way to understand the subject beyond the first couple of paras, if that. (Nor would they willingly choose to read the ISO standard.) If they did, they would find the wikipedia article discusses photographic exposure in the context of sensitivity "An appropriate exposure for a photograph is determined by the sensitivity of the medium used." And this is what most photographers do rather than worry about the definition of exposure.

This is where the trouble starts: a thread on the forum mentions the 'exposure triangle', which immediately gets diverted into an argument about strict terminology, and away from the practical process of setting a camera to achieve a acceptably exposed image. I'm certainly not arguing about the correctness of the definition - just whether insisting on the definition in common photographic speech (e.g. as in exposure triangle, exposure compensation) is important/relevant/helpful.

Edited yesterday at 04:58 PM by LocalHero1953

[pgk]

The exposure triangle was and is an approximation intended as guidance for controlling three elements used to obtain similar exposures. As such it needs to be appreciated that it is not definitive. Its a good practical solution for adjusting the base parameters surrounding exposure but, as with all discussions on the net, accepting it to be more than it is will eventually lead to problems. Photography is, in essence, simple, but as with most simple things, the devil is in the detail. Exposure is simply a matter of matching shutter speed and aperture to enable a specific quantity of light to fall on a light sensitive surface, but actually it is far more complicated in that we demad a lot of peripheral requirements too. We want clean, noise free images, but these demand minimal gain (low ISO - so that we maintain the optimal quantity of light) and this imposes restrictions on our base assumption, as might movement, need for much to be in focus, desire to retain highlight detail and many other parameters. Simplifying things is not so simple.

[SrMi]

50 minutes ago, LocalHero1953 said:

This is where the trouble starts: a thread on the forum mentions the 'exposure triangle', which immediately gets diverted into an argument about strict terminology, and away from the practical process of setting a camera to achieve a acceptably exposed image.

The situation is similar to the misinformation that ISO changes sensor's sensitivity (mainly espoused by people who talk about exposure triangle). Should we ignore it or react?

Considering that the AI models are amplifying any incorrect information found on the web, and that AI is becoming a trusted source for many, I think we should be active against any misinformation.

[Jeff S]

I read recently that some guy died from exposure at 10,000 feet. I guess one should also consider altitude when determining proper exposure.

[IkarusJohn]

The issue for me comes down to how the terminology impacts on my photography.  I agree that words matter - precise use of words is my profession, after all.  And, I’m grateful to @SrMi for taking the time to explain his point of view.  To be honest, “exposure triangle” was not a term I was familiar with til this discussion.  I don’t read marketing blurb.

I set aperture for depth of field, shutter for acceptable motion blur (or lack of it) and keep ISO within tolerable reach of base ISO for the sensor (360 for the Monochrom, 64 for the X2D and 100 for the M10-D).  Though I will often set ISO to Auto with my Monochrom.

But, does confusion or misleading mixing of exposure and amplification result in more than imprecise language?  Well, technically, at risk of dancing on the head of a pin.  If you use ISO as an “exposure” adjustment, you’re actually playing with the quality of the digital file you get to download, rather than adjusting the quality of the light hitting the sensor (exposure).  While an image taken at base ISO may give the “best” result possible from your sensor, that only works if the exposure results in the image you wanted.  It’s when you hit the “brightness” slider in LightRoom (digital amplification) that things get tricky.

The simple point, without diving into Srmi’s favourite topic, ISO invariance, is that increasing gain (analogue amplification within the extended ISO) in camera by raising ISO is not the same as raising the brightness slider in LightRoom (digital amplification), provided you’re not moving into “simulated” ISO in your camera settings.  Put simply, each camera has an ISO range where “analog amplification” within the extended range has benefits which can’t be gained in post production.  Beyond that “extended range” you’re into simulated ISO where there’s no benefit to in camera adjustment over post processing.

Lots of terminology, but what does it mean?

While you may lose some image quality benefit moving away from base ISO, if you stay within your camera’s extended ISO range, you will get less processing noise than if you just rely on adjusting brightness in post.  Conversely, if you just treat ISO as another exposure setting and move out of the extended range (into simulated ISO) then your image quality will suffer - you won’t gain any in camera benefit over just moving the sliders in post.

In most cases, adjusting ISO to maintain the aperture and shutter settings you want (the triangle of exposure) won’t matter, provided you stay within your camera’s extended base ISO range where range.  In post, you will get a more useable file than if you stayed at base ISO.  Where the “triangle” falls apart is when you get aggressive with ISO adjustment, and move into simulated ISO ranges.

For an ISO invariant camera, you won’t amplify any noise in post, so you can take all your images at base ISO and move your sliders at will.

I have no idea where the extended range begins and ends with my cameras, so I tend not to stray too far from base ISO.

A more precise explanation here - https://photographylife.com/iso-invariance-explained

[jaapv]

2 hours ago, LocalHero1953 said:

"An appropriate exposure for a photograph is determined by the sensitivity of the medium used."

And there is the basic misunderstanding: Raising ISO does not change the sensitivity of the sensor.

[jaapv]

40 minutes ago, IkarusJohn said:

While you may lose some image quality benefit moving away from base ISO, if you stay within your camera’s extended ISO range, you will get less processing noise than if you just rely on adjusting brightness in post.

Only if the camera itself applies noise reduction.  If you use the exposure slider in post  -which you should in this case- you are doing something different from raising brightness. It involves various contrast parameters and gamma as well. Brightness can also be changed by using "multiply" which is the control to use when preparing a print, by "dehaze" or nowadays by the "adaptive" colour profile (AI).

[IkarusJohn]

6 minutes ago, jaapv said:

Only if the camera itself applies noise reduction. 

No, that isn’t the point at all.

[jaapv]

7 minutes ago, IkarusJohn said:

No, that isn’t the point at all.

It is not a point.

[IkarusJohn]

1 minute ago, jaapv said:

It is not a point.

Helpful.

[jaapv]

Snap.

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[IkarusJohn]

So, to progress this discussion, what cameras are, or are approaching, ISO invariance?