The Exposure Triangle Is Misleading And Unnecessary.

The GFX 50S stops applying gain to the numbers in the raw file image after ISO 1250. The GFX100s keeps on increasing the numbers as you turn the ISO dial up. Both cameras are ISOless above ISO 1250. I know because I've measured the input-referred read noise vs ISO for both cameras. I've also looked at the histograms of dark-field images with varying ISO settings.

How does it affect my photography? I have no qualms about using the ISO settings above 1250 on the GFX 50S. I don't use those settings at all on the GFX 100S.

The exposure triangle does not exist. When people use the term exposure triangle to help new photographers, they are actually describing an image brightness triangle. The problem is conflating an aesthetically useful, perceived image brightness with an image that has the highest practical signal-to-noise ratio. Here practical refers to minimizing loss of resolution caused by camera or subject motion and, or an effect lens DOF.

Unfortunately, image brightness has little to do with optimizing technical image quality (a.k.a. data information capacity). Data information capacity is a function of the system resolution and raw file SNR. Camera ISO setting has no affect on resolution (unless the camera supports pixel binning). But an ill-chosen camera ISO setting will result in an needlessly low SNR.

With respect and thanks to all the expert contributions in this thread, it's now way more than the 90 posts I started at, and the beginners thread has also been summoned yet, despite reading all the answers and consulting that beginners thread, I find my self even more confused that before we started. I'm 60 years old and started photography aged 13, successfully operated my own B&W darkroom for D&P, used the Zone system, processed E6 slidefilm, started digital in 1999, and definitely don't consider myself a beginner. However, a lot of conceptual baggage comes with all that which may block the path to understanding. And what I mainly want to understand is what is the purpose of the ISO dial and how should I use it for everyday photography. The engineering stuff is a bonus.

I'll summarise my conceptual starting point:

1. Back in the film days we were taught that in order to expose a film adequately in camera, we needed to consider the ambient light level, the film speed, the aperture and the shutter speed. Let's assume film speed is fixed (ignoring pushing etc), that meant we dialed the speed rating of our film into our light meters, pointed at something approx middle grey and got a reading which suggested different aperture/combinations that would yield a passable average exposure. Film speed was fixed, not a variable, unless you were AA processing individual sheet film.

2. Films of different speeds were available, it was important to enter the correct speed into our meters (whether manufacturer's rating or our own EI rating)

3. The exposure triangle idea was promoted to remind people that the exposure your meter recommended would be affected by the chosen shutter speed, aperture and film speed. All 3 variables were important to a correct light meter exposure suggestion. Conclusion 1: in those days, the exposure triangle concept seemed a reasonable didactic concept because film speed changed with different films.

4. With the advent of digital, things appeared to change. Digital cameras have this dial marked ISO. It appears to change the sensor sensitivity on the fly, acting as if you could magically swap out the sensor from shot to shot. Now, when considering light meter readings, film speed was no longer set once and forget, but could be reset for every shot. Conclusion 2: Voila! the exposure triangle is even more vital than before.

5. Then we learnt that conclusion 2 was bunk, because it is not possible to change the sensitivity of the sensor. Conclusion 3: Digital cameras are forever locked into to using a single film speed, the ISO dial does not change film speed! We still however need to set some kind of film speed into our meters, so the exposure triangle is still useful in the limited sense of Conclusion 1 (base ISO varies between cameras)

Having learned one thing with film, then another with digital, then having that declared null and void, where does that leave us?

• If the ISO dial can't increase the sensitivity of the sensor akin to swapping in a faster film, what does it do that is useful photographically?

• Am I better off leaving it at base ISO, forgetting about that dial, considering my sensor as one film speed only and underexposing 5 stops or should I raise the ISO when it's dark to persuade my camera to use a fast enough shutter speed to avoid ruinous camera shake ?

• Why do cameras even have an ISO dial?

On the surface, this whole issue seemed incredibly straight forward and simple Yet it clearly isn't and generates much debate, confusion and misinformation.

At this point of time, having read all this stuff, I now find myself in the position of having no idea what the ISO dial is for and when to use it, which after 47 years of using a camera as a serious amateur is a quite sad situation. But, painful as it is to unlearn long believed stuff, if that is what we need to do, that is what we need to do.

It would be helpful to me to have a written down simplified rule of thumb explanation (that doesn't go deep into engineering and philosophy or need to be 100% technically accurate. Interesting as technical accuracy is, when a cheetah is sprinting past at high speed, you really need an instantaneous rule of thumb to guide your choice of settings in the milliseconds you have to decide)...

Thanks

Dave

I don't know about that. Perhaps a different name was used, but the concept definitely existed in the 1970s. The exact name doesn't really matter.

I don't think it is possible to do that and have it apply to every camera made.

Here's what it looks like for one camera:

blog.kasson.com/gfx-100/fuji-gfx-100s-exposure-strategy/

David,
Forget about the sensor. What matters are the camera and the photograph.

The effect of the ISO setting with JPEG images is much stronger than with RAW. Some cameras are “ISO Invariant.” As I understand, this means that you can shoot the same exposure at multiple ISO settings from 100 to 56,000, and the RAW image will be the same, and you can adjust brightness any of those photos with your RAW editor and get the same result.

My Canons are not like that. I tested them. The ISO setting definitely affects the RAW files. Is that because of the way the sensor works, or because of firmware inside the camera? Guess what? It doesn’t actually matter, does it? If I’m going to reduce my shutter speed and keep aperture constant, I need to increase the ISO setting. So that three-sided shape dynamic is there, no matter how much people dislike the expression :-)

It causes push ;)

Exposing 5 stops lower means capturing 5 stops less light.

By mistake ;)

I was doing a lot of photography in the 1970s, and I don't remember any mention of triangles.

Don

I have consulted my edition of Michael Langford's classic college text book "Basic Photography". He makes no mention of the term "exposure triangle". But in the section about light meters, he makes it quite clear that film speed, shutter speed and aperture are the 3 key parameters. That's the exposure triangle concept, if not "Exposure Triangle" TM. The exposure triangle name is just a catchy term for those 3 things to my mind, so it is as old as photography. What's newer, is the damn mysterious ISO knob on my cameras that seems to have replaced film speed as a parameter even though it isn't film speed. What it is, is exercising me now. Especially after spending the morning in bright sunshine pouring over maps for a shooting location only to have a monsoon pour down all afternoon leaving me twiddling my ISO dial....

Trying to rephrase the whole question in my head.

If (in a parallel universe) it were possible to varying the photoelectric effect, such that a photon hitting a photosite could kick out more than one electron, and we added a control to our cameras labelled "Sensitivity" that controlled this, would the exposure triangle then apply to digital cameras? For example, if we could set the control to produce 2 electrons, 3 electrons, 4 electrons etc for each photon.

To my simple mind, this sounds very much like having a variable sensitive sensor akin to swapping out Velvia 25 for Tri X (assuming it didn't collapse the false vacuum) :-)

EDIT: while waiting for a communications genius smart enough to come up with an explanation suitable for someone as stupid as me, I googled the phrase "exposure triangle". It's everywhere! Quote by just about any photographic resource you can find from B&H to Adobe. I honestly thought it was just a throw-away phrase. I can see how something so ubiquitous can do a lot of harm if it is wrong, and why responsible adults may be upset by its existence.

Mind you, one of the more hilarious objections I came across was a site where the author treated the exposure triangle as if it were geometry and tried to show it was incorrect by drawing actual triangles to reflect adjustments to the settings and complaining when said triangles failed and made no geometric sense. Correct or incorrect, it's a metaphor, you can't perform geometric transformations on a metaphor then complain it's mathematically incorrect!

I don’t honestly understand what are the correct and incorrect ways to think about my exposure settings while I shoot. Sincerely, how should I think?

Sometimes I nail it and sometimes I don’t. Most of the times when I get it wrong, it’s not the settings I’ve chosen but rather the nature of the light falling on my subject. Or I missed focus.

Years ago, I would drive to an island before dawn every Saturday, to photograph the SF Bay Bridge. Once I worked out the ideal spot and the ideal exposure settings… it all came down to light. Some days it rained. Some days there was fog. It went on like that for two months until I got the shot I wanted. It’s not just about thinking right and setting your camera right.

The viewer doesn’t care if the lighting was bad, or if it was hard, or if your foot hurt. They definitely don’t care about how you were thinking.

4, as it is light meters section, light is one of those.
And, key parameters to what?

Key things you can adjust on your camera to get different exposures.