Rant warning...ISO, ISO and the exposure triangle myth

[Bored Gerbil]

A lot of Olympus cameras are not ISO invariant. For example, the new OM1 has a 3 gain stage design...

cheers Kevin

 

[ahaslett]

Thank you, that is very helpful.

In other words, there is a lot going on behind the scenes there, as I suspected.

-J

I only hope I got it mostly right! Thankfully there are a lot of helpful people here, even if they get shouted down sometimes.

It would be wonderful if cameras had a RAW mode and a jpeg mode. Then I could set most things to auto or base, choose my mode, set how to use the DR and leave it to the OEM to manage exposure (in A or S), gain etc.

Then making an image from the RAW would be down to me. The image in the EVF would allow composition, and the meta data would give “as shot” ISO and WB temperature.

Instead you have to reverse engineer something designed to produce jpegs, which gets complicated. You can get reasonably close, so I’m not that worried. Using UniWB is a bit of a pain.

Andrew

 

[Bassam Guy]

Do you think perhaps its auto ISO thats made things feel different?

We could select an ISO for a shoot like we did with film and make the same steps with shutter speed and aperture?

I know you're right about the technicalities, but it feels like the only real change is not having to shoot 24 or 36 shots at the same ISO.

Admittedly I only shot film as a child/teen and it wasnt a great passion so I cant claim to know how it felt to shoot like I do with MFT these days!

As an old-timer I can say the film days were wonderful. We never argued over megapixels or equivalence.

Surely there were arguments about one film versus another. There was probably camp Kodak and camp Fuji, both fiercely defending their chosen emulsion. And when they got tired of that, they probably tried to confuse us with “reciprocity failure”, which might have been about whose turn it was to buy lunch but was probably about when the exposure triangle didn’t look like a triangle anymore.

No, photographers never argued. No one even browsed DPR forums. The entire photographic world was perfectly harmonious in every way. Most important, no one ever responded seriously to sarcasm

Reciprocity Failure is a real thing and should not be belittled, even if it seems trivial to you.

 

[offtheback]

Does that only work with ISO invariant sensors?

 

[JohnnyLuddite]

.....

As an old-timer I can say the film days were wonderful. We never argued over megapixels or equivalence.

Surely there were arguments about one film versus another. There was probably camp Kodak and camp Fuji, both fiercely defending their chosen emulsion. And when they got tired of that, they probably tried to confuse us with “reciprocity failure”, which might have been about whose turn it was to buy lunch but was probably about when the exposure triangle didn’t look like a triangle anymore.

Funnily enough, I think there was more tolerance and camaraderie with film than I've seen in digital - perhaps because it was harder to get good shots. It's true that I'm still mourning Kodachrome 25, but never felt a need to defend it or attack someone else's choices. And I'm still taking film in small quantities (Portra 160).

Yet on this site, I've witnessed vituperative arguments against different models from the same vendor as if there were some doctrinal argument meriting auto da fe. Supposedly there is some secret sauce, magical rendering of colors etc. And don't get me started on the "legendary" moniker. All quite tedious.

 

[JohnnyLuddite]

......

Reciprocity Failure is a real thing and should not be belittled, even if it seems trivial to you.

True, although there was the upside of highlight protection kind of built in. Switching to digital, that was one of the biggest changes of discipline, having to attend to avoiding blown highlights - I guess I had got lazy with film on that score.

 

[2ndact scene1]

.....

As an old-timer I can say the film days were wonderful. We never argued over megapixels or equivalence.

Surely there were arguments about one film versus another. There was probably camp Kodak and camp Fuji, both fiercely defending their chosen emulsion. And when they got tired of that, they probably tried to confuse us with “reciprocity failure”, which might have been about whose turn it was to buy lunch but was probably about when the exposure triangle didn’t look like a triangle anymore.

Funnily enough, I think there was more tolerance and camaraderie with film than I've seen in digital - perhaps because it was harder to get good shots. It's true that I'm still mourning Kodachrome 25, but never felt a need to defend it or attack someone else's choices. And I'm still taking film in small quantities (Portra 160).

Yet on this site, I've witnessed vituperative arguments against different models from the same vendor as if there were some doctrinal argument meriting auto da fe. Supposedly there is some secret sauce, magical rendering of colors etc. And don't get me started on the "legendary" moniker. All quite tedious.

Mr. Luddite, maybe the main difference is that there was no DPReview, no anonymous screen names and not even an internet. Just letters to the editor that may or not get published (and the ones with too much attitude would not get published). I would also think there was genuine respect for the people who could make the difficult medium of film produce incredible images. Based on the roll I picked up from my lab a couple days ago, I am clearly not in that category!

Interesting thought: when I just typed “Mr Luddite” above, my spell checker actually typed “Me Luddite”. Spell checkers now apparently have AI!

 

[2ndact scene1]

Do you think perhaps its auto ISO thats made things feel different?

We could select an ISO for a shoot like we did with film and make the same steps with shutter speed and aperture?

I know you're right about the technicalities, but it feels like the only real change is not having to shoot 24 or 36 shots at the same ISO.

Admittedly I only shot film as a child/teen and it wasnt a great passion so I cant claim to know how it felt to shoot like I do with MFT these days!

As an old-timer I can say the film days were wonderful. We never argued over megapixels or equivalence.

Surely there were arguments about one film versus another. There was probably camp Kodak and camp Fuji, both fiercely defending their chosen emulsion. And when they got tired of that, they probably tried to confuse us with “reciprocity failure”, which might have been about whose turn it was to buy lunch but was probably about when the exposure triangle didn’t look like a triangle anymore.

No, photographers never argued. No one even browsed DPR forums. The entire photographic world was perfectly harmonious in every way. Most important, no one ever responded seriously to sarcasm

Reciprocity Failure is a real thing and should not be belittled, even if it seems trivial to you.

Perhaps this was sarcasm failure.

 

[dbdalrymple]

Very effective troll Tom. It covered enough bases to produce many conflicting responses, produce little coherent response and deeply bury the coherent responses. And it's in the wrong forum. How did you select the MFT forum as the right place for this?

Dale B. Dalrymple

 

[Interceptor121]

It is true that exposure is only determine by lens aperture and exposure time however it is also not true that a camera has only one ISO

A sensor has a typical sensitivity and saturation value and an on-board PGA amplifier and an array of AD converters.

The manufacturer makes a decision to define what the base gain is (no camera has no gain) and this defines the base ISO.

There are many compromises that go on because the sensor output is not actually completely linear so in my mind the whole idea of this simplification has to be reviewed as very few phenomena in nature are linear.

From a practical point of view increasing gain (ISO) improves SNR while it reduces the peak brightness that can be handled so having an exposure triangle does send a good message in terms of not leaving the ISO at base when your image is underexposed.

Exposure triangle right or wrong it is has been accepted as a concept as long as it is well understood the role of each party we can leave it as is

 

[alfn]

In the ‘old days’ we used film which had its sensitivity rated in something, ASA, ISO or DIN. In considering exposure, and remembering that you had to get it right because there was no effective post processing of negatives or slides, it was necessary to consider the film sensitivity (I’ll call it ISO) when setting aperture and shutter speed. So the concept of an exposure triangle developed, where the three parameters of ISO, F stop and shutter speed had to be taken in to account and could conveniently be expressed as a triangle, each parameter affecting the others.

I would suggest that in the digital age, the ‘exposure triangle’ is dead and should not be mentioned again. All cameras have just one ISO which is the base ISO which can be used to calculate the ‘best’ exposure, and that ISO is not usually variable. Under normal conditions that exposure would be one which optimally captured enough light to fill the pixel ‘buckets’ (for special effects some other exposure else might be used) We have lost one of the variables which formed the ‘triangle” which has therefore become only two dimensional.

However we now have a second use of the term ‘ISO’ to reflect the amplification performed in camera to display what might be a very dark image captured (if the pixel buckets are not filled) as something half decent. Almost essential if the image is output as JPEG for instant viewing on the LCD, much less essential if PP is going to be done where the same effect can be achieved by exposure correction or lightening. (I am ignoring the beneficial effects of in camera gain on some types of noise, or of dual gain systems)

So we get the frequent use of terms like ‘shooting at high ISO’ when we really mean ‘shooting underexposed’. The use has become so pervasive that it is hard to avoid, even for those who understand.

We do need to amplify the sensor signal to give decent pictures, especially at the P&S and JPEG end of the market.

Should we have a new term for what we are doing?

Can we bury the ‘exposure triangle’ thing?

If I have this all wrong, I am sure you will let me know

tom

It is important to distinguish between shooting SOOC Jpegs and shooting raw. In the first instance, the ISO sensitivity setting (as the ISO call it in ISO12232:2019) behaves exactly like with a film camera: increasing or decreasing the effective sensitivity of the digital camera. And, yes, it is part of the exposure triangle.

When shooting raw the ISO control becomes largely irrelevant on most modern cameras except for certain practical purposes such as viewing, previewing and so on. The whole subject being horrendously complicated and VERY tedious.

This is all explained in ISO 12232:2019.

Personally, I always shoot Jpegs, as the camera manufacturer intended, except for certain specialised purposes such as astrophotography when raw files are necessary for stacking and each camera has an optimum ISO noise setting irrespective of subject or exposure.

In short, it isn't a question of burying the exposure triangle: it is simply a question of whether you personally find it useful or not.

 

[tedolf]

Please be advised that there is one former forumer (may he rest in peace) who was banned for repeatedly banging this drum and getting in to 150 post arguments with other forumers over this issue.

Tedolph did not participate but found it very entertaining.

Tedolph