iso as an exposure variable - not.

[Patrice]

Some of the responses in an another thread introduce the control of iso as having an active roll in controlling exposure. 'Exposure triad' is even being bandied about. What a load of s...!

Now that I have your attention, let me explain my point.

I propose that photography is about creating an image with light. I further propose that a 'well exposed image' is an image that conveys the vision of the photographer in terms of mood, content and composition. We don't need to get into discussions about blown highlights or lack of detail in shadows. After all, there is nothing wrong with an 'overexposed' image if that is what the intent of the photographer was.

We have two (not three) controls that have a direct effect on the content and composition of the image: aperture and shutter speed.

We control the depth of field with the aperture and the appearance of motion and the freezing thereof with the shutter speed. Only when we can not achieve or vision with those two controls do we then need to move into controlling the iso. Changing the iso from the camera's base adds nothing compositionally to the image other than adding amp noise. (Unless what we want to create is an image grainy with amp noise.)

When the time comes we can selectively change the iso in different sections of the sensor (think progressive ND filters) then we can start talking about iso having an active roll in exposure, ie: having an active roll compositionally and of an 'exposure triad'.

Changing the iso is the same as loading faster film in the camera. Aperture and Shutter still control the image content. In fact changing film did have a somewhat more active roll than 'sensor sensitivity' in that the different films had very different characteristics in their response to light. Think of the lovely pastels of some Kodak emulsions and the vivid primaries of some Fugi offerings.

 

[oldmacman]

When you popped in a new roll of film, what other dial did you set to let your camera know that you had faster or slower film? ISO is something you control by setting a dial on your camera. The fact that your exposure does indeed change if you forget to alter your ISO reinforces that fact. Many cameras handle higher ISO with ease and only making subtle differences to IQ. This thread seems to be an argument in semantics. When I teach photography I talk about the exposure triangle and point out what changes by altering any of those three settings.

 

[Overread]

I think you're confusing things and presenting a false truth that is going to confuse new people.

Exposure triad is indeed made up of aperture, shutter speed and ISO by considering each of the controllable variables and their own influence on the light that one has to work with. This is excluding ideas of composition and content and purely focusing on the light itself - you cannot deny that ISO is a key part of the exposure just as different speed films were a key part of an exposure in the past.

What you are more talking about isn't just the exposure but the appearance of the exposure itself and there I would somewhat agree that shutter speed and aperture create a major factor in what the final shot will look like. However this is not the same as saying that ISO is not a part of the exposure component. Furthermore its somewhat ignoring the noise factor of ISO as well as the fact that progressively higher ISOs will reduce the dynamic range possible with the camera.


In addition it somewhat suggests that ISO is outside of the aperture and shutter speeds influence on exposure which is very wrong - a well controlled and exposed shot with a high ISO can look cleaner than an underexposed shot with a lower ISO (this of course within reason)

 

[c.cloudwalker]

I propose that ...

You propose whatever you want but it makes no difference. Changing the ISO (whether with a film or digital camera) changes your exposure parameters. Get over it.

The fact that in the film days this could only be done on the fly with some MF and all LF cameras is of no importance. Today, with digital cameras, you can change your ISO as you go. So what? Who cares?

But it does affect your exposure. So, yes, you can say that today ISO is part of the exposure control. And so, yes, you have three (3) controls for your exposure.

 

[Garbz]

This is the biggest load of crap I have ever heard. You can't achieve a desired image with two controls. Suppose you want an image that is tac sharp and has a large depth of field, but it's dark outside. What do you do? Given what you say you have two options:

a) Take the wonderfully composed picture that is 4 stops to high and marvel at your pitch black masterpiece.
b) Cry like a baby because you can't get the photo you desire.


Photography is definitely about creating a picture with light and the sensitivity of you're recording medium is one of the three variables that must be harmonised in order to create the picture you want. Otherwise you're back to the above two options when things go wrong.

Also if you believe exposure doesn't effect the overall composition of the image I would like to sell you this wonderfully composed picture of a horse:

 

[Josh66]

Some of the responses in an another thread introduce the control of iso as having an active roll in controlling exposure. 'Exposure triad' is even being bandied about. What a load of s...!

Now that I have your attention, let me explain my point.

I propose that photography is about creating an image with light. I further propose that a 'well exposed image' is an image that conveys the vision of the photographer in terms of mood, content and composition. We don't need to get into discussions about blown highlights or lack of detail in shadows. After all, there is nothing wrong with an 'overexposed' image if that is what the intent of the photographer was.

We have two (not three) controls that have a direct effect on the content and composition of the image: aperture and shutter speed.

We control the depth of field with the aperture and the appearance of motion and the freezing thereof with the shutter speed. Only when we can not achieve or vision with those two controls do we then need to move into controlling the iso. Changing the iso from the camera's base adds nothing compositionally to the image other than adding amp noise. (Unless what we want to create is an image grainy with amp noise.)

When the time comes we can selectively change the iso in different sections of the sensor (think progressive ND filters) then we can start talking about iso having an active roll in exposure, ie: having an active roll compositionally and of an 'exposure triad'.

Changing the iso is the same as loading faster film in the camera. Aperture and Shutter still control the image content. In fact changing film did have a somewhat more active roll than 'sensor sensitivity' in that the different films had very different characteristics in their response to light. Think of the lovely pastels of some Kodak emulsions and the vivid primaries of some Fugi offerings.

You contradicted yourself in your own post...

Yes, it is all about achieving the photo you envisioned - and ISO is just one tool to help you do that.

 

[inTempus]

 

[c.cloudwalker]

Btw, grain and noise are two different things.

Grain is found in film photography while noise belong to the digital world. And it doesn't look quite the same.

 

[Derrel]

ISO is an exposure variable...in every,single shot made...every morning, afternoon,and night...bracketing via ISO index shifting and push- and pull-processing is a time-honored TRADITION in much commercial photography work where the aperture must remain at a specific f/stop value to control depth of field. Minor 1/3 and 2/3 EV value ISO adjustments are a very time-honored way to get flash exposures that hug to the right hand side of the histogram when shooting in RAW mode. The ISO value in use is a critical,basic part of the exposure equation. It is an essential factor. As in "essential", not optional.

Sorry...nice try...but the premise of this original post is totally,totally "out there" and, uh, 'wrong'...in big ol' air-quotes...

 

[manaheim]

Hey guys, I say let her nail her left foot to the floor. Why not? If she would like to think that ISO is not a part of the equation, by all means let her do so. The rest of us can point and chuckle.

BTW, Patrice, if you're going to go off on a tirade like this you might want to at least know the difference between roll and role.

 

[timbearden]

I can't stop laughing.......ISO being irrelevant? First I thought someone probably told her that Nikon deals with ISO better than Canon and that she was trying to find a way to reason keeping her Canon. Then I looked and found out she has a Nikon. So now, I being totally perplexed, am still laughing.

I can't wait till she posts a photo using an ISO of 25,600 and it is one big dot, or maybe a couple dots. Her excuse will be that it was her intent to create a big dot, or a mess of noise. This is like abstract expressionism to the old masters. No wait.....pointillism. At least pointillism actually looks decent.

 

[Patrice]

... you might want to at least know the difference between roll and role.

That was a rather careless piece of post proofreading, sorry.

BTW, Patrice, if you're going to go off on a tirade like this ...

One post does not a tirade make. (I might go on a crusade and I might shoot a tirade, but it would be difficult to go on a tirade.)

I did not mean to offend anybody and I certainly did not aim my 'tirade' at anybody either.

This seems to have touched a sensitive nerve in some. Thank you oldmanmac, Overread and Derrel for your responses. Your posts provided solid information and supported a considered point of view.

You might also argue that in a broader sense a few other factors have an affect on a photograph viewer's impression of a good exposure. On camera control of white balance, and maybe even more so, the effect of additional lighting and it's modification have a very profound effect on the image. Furthermore, why not include post processing. Critiques to photographic submissions very often advance advice on lighting, aperture, white balance and also shutter speed. However we very seldom see ' ... nice job with your selection of iso, well done!'

When someone asks about exposure control in shutter priority mode the answer is not only to vary the iso as has been promulgated in some recent threads. To say "... when in tV mode iso controls your exposure" is in my opinion an incomplete answer. Variation of the aperture is very much a valid option, probably more so.

We are lucky that we can now change the 'film' instantly in our cameras. The press of few buttons enables us to vary white balance and iso very conveniently. That has not always been the case, once the film was loaded you then only had aperture and shutter speed as 'on camera' controls. Modifying the light and adding filters to the front of the lens were and are still very effective additional means of controlling exposure, albeit with off camera controls. However, within the context of on camera controls, I still believe that the variance of iso away from the sensor's base value is mostly undertaken only when the combination of aperture and shutter speed will not enable us to create the image we want.

(manaheim, I was not aware of an unnoticed sex change I have fathered four children and it would be a shame for it to all have been a big mistake)

 

[prodigy2k7]

... you might want to at least know the difference between roll and role.

That was a rather careless piece of post proofreading, sorry.

BTW, Patrice, if you're going to go off on a tirade like this ...

One post does not a tirade make. (I might go on a crusade and I might shoot a tirade, but it would be difficult to go on a tirade.)

I did not mean to offend anybody and I certainly did not aim my 'tirade' at anybody either.

This seems to have touched a sensitive nerve in some. Thank you oldmanmac, Overread and Derrel for your responses. Your posts provided solid information and supported a considered point of view.

You might also argue that in a broader sense a few other factors have an affect on a photograph viewer's impression of a good exposure. On camera control of white balance, and maybe even more so, the effect of additional lighting and it's modification have a very profound effect on the image. Furthermore, why not include post processing. Critiques to photographic submissions very often advance advice on lighting, aperture, white balance and also shutter speed. However we very seldom see ' ... nice job with your selection of iso, well done!'

When someone asks about exposure control in shutter priority mode the answer is not only to vary the iso as has been promulgated in some recent threads. To say "... when in tV mode iso controls your exposure" is in my opinion an incomplete answer. Variation of the aperture is very much a valid option, probably more so.

We are lucky that we can now change the 'film' instantly in our cameras. The press of few buttons enables us to vary white balance and iso very conveniently. That has not always been the case, once the film was loaded you then only had aperture and shutter speed as 'on camera' controls. Modifying the light and adding filters to the front of the lens were and are still very effective additional means of controlling exposure, albeit with off camera controls. However, within the context of on camera controls, I still believe that the variance of iso away from the sensor's base value is mostly undertaken only when the combination of aperture and shutter speed will not enable us to create the image we want.

(manaheim, I was not aware of an unnoticed sex change I have fathered four children and it would be a shame for it to all have been a big mistake)

Funny, my old film camera has a control for setting the ISO.

And there is a huge difference between white balance, and exposure... :er:

 

[shaunly]

LOL!! ! this made my day:lmao::lmao:

 

[altopiet]

Funny, my old film camera has a control for setting the ISO.

Yes, and as I remember, you inserted a film with a fixed ASA/ISO value, and could not change that while using that film?

That has not always been the case, once the film was loaded you then only had aperture and shutter speed as 'on camera' controls