Help me to understand how iso, shutter speed and aperture interact

[FrancoD]

1. Bill Ferris wrote:

What? The op asked about the relationship of the settings to each other and how they interact which is exactly what the exposure triangle does.

Except, it doesn't. It represents and is used to teach a mythical reality in which ISO, shutter speed, and aperture determine exposure; in which ISO alters the sensor's ability to collect light; and in which ISO is the source of noise in photos.

Relativity can be used to prove that Earth is flat:

https://theflatearthsociety.org/home/index.php/blog/einsteins-relativity-proves-earth-flat

This doesn’t make relativity wrong.

Every time a new user asks about exposure, experts devolve into arguments about whether ISO is an exposure control or not, and the original poster is left baffled.

I think we’d all serve this community better if we all avoided such arguments.

If some of the members here were primary school teachers they would ,on the first day of school, start by teaching algebra. You know, to make sure the kids get it right from the beginning.

not of course that my comment will register with them....

 

[John Sheehy]

1. bjn70 wrote:

You can search the internet for "exposure triangle".

ISO adjusts how the camera electronics respond to the amount of light hitting the sensor. A higher number allows you to create an image from less and less light, but adds digital noise to the image.

The camera does add some digital noise that might become a problem if you are into serious astrophotography. However, the noise we typically see in photos, shot or photon noise, comes from the (lack of) light itself. For most practical purposes, the noise that camera "adds" is insignificant.

For whose practical purposes? The tripod-toting architectural photographer, perhaps, but people using hand-held high magnification for active subjects live ankle-deep, knee-deep, or even waist-deep in read noise, and so there is no reason to talk in a general sense as if read noise is a thing of the past. Put any 4 recent FF sensors into the DPR studio comparison tool in "Comp" mode and incandescent mode, at the highest ISO they all support in the tool, and you may see big differences in noise, almost all of which is differences in read noise (except the Sony-A9-III, which has photon noise typical of smaller sensors, due to its low QE).

In fact, all the buzz about noise differences due to 12-bit vs 14-bit, and fast readout vs slow, with the same sensor, is about post-gain read noise differences, only.

 

[John Sheehy]

ISO adjusts how the camera electronics respond to the amount of light hitting the sensor. A higher number allows you to create an image from less and less light, but adds digital noise to the image. Use the lowest number you can get away with.

Actually, the camera "adds" the same or less noise at higher ISOs, with very few exceptions, like the Panasonic FZ50 and one early Kodak and one early Leica digital camera, IIRC. It is the decreased exposure that is typical of "normal" or standard exposure at high ISOs that causes the lower signal-to-noise ratio.

 

[Michael Fryd]

1. Bill Ferris wrote:

What? The op asked about the relationship of the settings to each other and how they interact which is exactly what the exposure triangle does.

Except, it doesn't. It represents and is used to teach a mythical reality in which ISO, shutter speed, and aperture determine exposure; in which ISO alters the sensor's ability to collect light; and in which ISO is the source of noise in photos.

Relativity can be used to prove that Earth is flat:

https://theflatearthsociety.org/home/index.php/blog/einsteins-relativity-proves-earth-flat

This doesn’t make relativity wrong.

Every time a new user asks about exposure, experts devolve into arguments about whether ISO is an exposure control or not, and the original poster is left baffled.

I think we’d all serve this community better if we all avoided such arguments.

If some of the members here were primary school teachers they would ,on the first day of school, start by teaching algebra. You know, to make sure the kids get it right from the beginning.

not of course that my comment will register with them....

It's not that they would start teaching algebra, it's that they would be careful to use the correct words for addition and subtraction.

Now, if some parents gave them grief for using the correct words, they might get a little more technical in their explanation to the parents as to why it's helpful to use the correct words, even when explaining the basics to a beginner.

 

[FrancoD]

1. Bill Ferris wrote:

What? The op asked about the relationship of the settings to each other and how they interact which is exactly what the exposure triangle does.

Except, it doesn't. It represents and is used to teach a mythical reality in which ISO, shutter speed, and aperture determine exposure; in which ISO alters the sensor's ability to collect light; and in which ISO is the source of noise in photos.

Relativity can be used to prove that Earth is flat:

https://theflatearthsociety.org/home/index.php/blog/einsteins-relativity-proves-earth-flat

This doesn’t make relativity wrong.

Every time a new user asks about exposure, experts devolve into arguments about whether ISO is an exposure control or not, and the original poster is left baffled.

I think we’d all serve this community better if we all avoided such arguments.

If some of the members here were primary school teachers they would ,on the first day of school, start by teaching algebra. You know, to make sure the kids get it right from the beginning.

not of course that my comment will register with them....

It's not that they would start teaching algebra, it's that they would be careful to use the correct words for addition and subtraction.

Now, if some parents gave them grief for using the correct words, they might get a little more technical in their explanation to the parents as to why it's helpful to use the correct words, even when explaining the basics to a beginner.

as I already pointed out, you and your kind simply don't get it.

 

[Dem Bell]

You can search the internet for "exposure triangle".

ISO adjusts how the camera electronics respond to the amount of light hitting the sensor. A higher number allows you to create an image from less and less light, but adds digital noise to the image.

The camera does add some digital noise that might become a problem if you are into serious astrophotography. However, the noise we typically see in photos, shot or photon noise, comes from the (lack of) light itself. For most practical purposes, the noise that camera "adds" is insignificant.

For whose practical purposes? The tripod-toting architectural photographer, perhaps, but people using hand-held high magnification for active subjects live ankle-deep, knee-deep, or even waist-deep in read noise, and so there is no reason to talk in a general sense as if read noise is a thing of the past. Put any 4 recent FF sensors into the DPR studio comparison tool in "Comp" mode and incandescent mode, at the highest ISO they all support in the tool, and you may see big differences in noise,

Of course I will. But who does most of their shooting at the highest ISO? I don't even know what it is on any of my cameras. I have the whole set of Topaz AI tools, yet I still do 99% of my shooting at ISOs below 12800.

As far as a beginner is concerned, read noise is not an issue until it is, and shooting indoor basketball at ISO51200 is not usually where people start photography.

almost all of which is differences in read noise (except the Sony-A9-III, which has photon noise typical of smaller sensors, due to its low QE).

Or a better point to start would be to explain to a beginner that light is made of photons, and because of that, the photos that receive fewer photons will be more blotchy, no matter what super-duper technology we use to count these photons.

The main origin of noise in the photos is photon noise. That's a good place to start, IMHO.

 

[Bob A L]

Surely the original poster is sufficiently confused by now.

 

[Michael Fryd]

Surely the original poster is sufficiently confused by now.

Probably not.

He's heard a number of explanations. All of which will allow him to get by with the basics.

• Subject lighting affects how much light is captured.
• Aperture affects how much light is captured, and depth of field.
• Shutter affects how much light is captured and motion blur.
• ISO affects how dark or light the resulting image looks (it sets up the relationship between light captured and how dark/light the JPEG looks).
• Capture more light and the image has less noise.

He may confused as to what is meant by "exposure" or how a triangle explains the above. Depending on which explanation he relies on, he may or may not have problems should he want to learn more.

But I do agree that using incorrect terminology, or insisting on using a triangle to illustrate something with more than three factors, can be very confusing to a beginner. Especially if the triangle is intended as a graph, but the actual contents of the graph are omitted (as is the usual case presented to beginners).

 

[Bob A L]

 

[J A C S]

Surely the original poster is sufficiently confused by now.

Probably not.

He's heard a number of explanations. All of which will allow him to get by with the basics.

• Subject lighting affects how much light is captured.
• Aperture affects how much light is captured, and depth of field.
• Shutter affects how much light is captured and motion blur.
• ISO affects how dark or light the resulting image looks (it sets up the relationship between light captured and how dark/light the JPEG looks).

It would be important for a beginner to know that in auto modes, the ISO setting changes the f-stop and/or the shutter speed, so it does affect the exposure and the noise.

• Capture more light and the image has less noise.

He may confused as to what is meant by "exposure" or how a triangle explains the above. Depending on which explanation he relies on, he may or may not have problems should he want to learn more.

But I do agree that using incorrect terminology, or insisting on using a triangle to illustrate something with more than three factors, can be very confusing to a beginner. Especially if the triangle is intended as a graph, but the actual contents of the graph are omitted (as is the usual case presented to beginners).

 

[Michael Fryd]

Surely the original poster is sufficiently confused by now.

Probably not.

He's heard a number of explanations. All of which will allow him to get by with the basics.

• Subject lighting affects how much light is captured.
• Aperture affects how much light is captured, and depth of field.
• Shutter affects how much light is captured and motion blur.
• ISO affects how dark or light the resulting image looks (it sets up the relationship between light captured and how dark/light the JPEG looks).

It would be important for a beginner to know that in auto modes, the ISO setting changes the f-stop and/or the shutter speed, so it does affect the exposure and the noise.

All the beginner needs to know is that in Auto mode, the camera may adjust Aperture, shutter, ISO, or subject lighting (pop up flash).

The next step is to elaborate on how the photographer can choose to fix one or more of these variables, and allow the camera to adjust only the rest.

For instance, it is reasonable to show the beginner how to put the camera in Manual mode with Auto-ISO. This is a great way to teach with a digital camera.

The beginner can then play with aperture and shutter to see how they affect depth of field and, along with subject lighting, how the combination of the two affects image noise.

That's a great way of introducing the concepts that just wasn't possible with film. Which is why many who use a film based workflow don't think to use it.

The beauty of this is that this is a workflow that can be used on professional shoots. Set the wides aperture that yields sufficient depth of field. Use the slowest shutter that doesn't yield unwanted motion blur, and you are guaranteed the highest exposure (and therefore least noise) for the lighting conditions.

Teaching a beginner to use a fixed ISO tends to do them a disservice, unless they intend to be primarily shooting film.

.

But of course, full auto (including Auto-ISO) is a great way to get a beginner started. One only needs to move to aperture or shutter priority (with Auto-ISO) once the beginner wants to start controlling depth of field or motion blur.

Digital makes it possible for the beginner to start with the basics of framing, perspective, and other non-technical skills, and still produce great images.

• Capture more light and the image has less noise.

He may confused as to what is meant by "exposure" or how a triangle explains the above. Depending on which explanation he relies on, he may or may not have problems should he want to learn more.

But I do agree that using incorrect terminology, or insisting on using a triangle to illustrate something with more than three factors, can be very confusing to a beginner. Especially if the triangle is intended as a graph, but the actual contents of the graph are omitted (as is the usual case presented to beginners).

 

[J A C S]

Surely the original poster is sufficiently confused by now.

Probably not.

He's heard a number of explanations. All of which will allow him to get by with the basics.

• Subject lighting affects how much light is captured.
• Aperture affects how much light is captured, and depth of field.
• Shutter affects how much light is captured and motion blur.
• ISO affects how dark or light the resulting image looks (it sets up the relationship between light captured and how dark/light the JPEG looks).

It would be important for a beginner to know that in auto modes, the ISO setting changes the f-stop and/or the shutter speed, so it does affect the exposure and the noise.

All the beginner needs to know is that in Auto mode, the camera may adjust Aperture, shutter, ISO, or subject lighting (pop up flash).

... by moving along the path of an exposure triangle...

The next step is to elaborate on how the photographer can choose to fix one or more of these variables, and allow the camera to adjust only the rest.

For instance, it is reasonable to show the beginner how to put the camera in Manual mode with Auto-ISO. This is a great way to teach with a digital camera.

The beginner can then play with aperture and shutter to see how they affect depth of field and, along with subject lighting, how the combination of the two affects image noise.

That's a great way of introducing the concepts that just wasn't possible with film. Which is why many who use a film based workflow don't think to use it.

The beauty of this is that this is a workflow that can be used on professional shoots. Set the wides aperture that yields sufficient depth of field. Use the slowest shutter that doesn't yield unwanted motion blur, and you are guaranteed the highest exposure (and therefore least noise) for the lighting conditions.

Teaching a beginner to use a fixed ISO tends to do them a disservice, unless they intend to be primarily shooting film.

"Fixed ISO" is not so fixed because you can adjust it.

The problem with what you advocate is that it is not so universal. Sometimes the light is so low, that you sacrifice the DOF, and change the idea of the shot to accommodate it. In low light, I would often put a fast prime, and that would make me shoot differently. Same with the shutter speed. When I shoot concerts, for example, I would go to slow speeds like 1/60 or even 1/30 sometimes, wait for the right moment, or take a few shots, hoping that some would be sharp enough. In other words, there is a balance you may want to achieve between noise, DOF, and motion blur, with some compromises in each one of them.

Also, in good light, I may decide that 1/125, f/8 is all I need and let the camera decide the ISO. The camera may very well compute ISO 25 then...

.

But of course, full auto (including Auto-ISO) is a great way to get a beginner started. One only needs to move to aperture or shutter priority (with Auto-ISO) once the beginner wants to start controlling depth of field or motion blur.

I did not mean exactly that. Fixed ISO and Av or TV are auto modes that are not "fully auto" like the green square.

 

[John Sheehy]

1. Bill Ferris wrote:

What? The op asked about the relationship of the settings to each other and how they interact which is exactly what the exposure triangle does.

Except, it doesn't. It represents and is used to teach a mythical reality in which ISO, shutter speed, and aperture determine exposure; in which ISO alters the sensor's ability to collect light; and in which ISO is the source of noise in photos.

Relativity can be used to prove that Earth is flat:

https://theflatearthsociety.org/home/index.php/blog/einsteins-relativity-proves-earth-flat

This doesn’t make relativity wrong.

That's an odd nonsequitor.

It is an empirical fact the Earth isn't flat. Any model that purports to "prove" the Earth is flat is flawed.

BTW, did you know the Flat Earth Society has members all around the world?

I thought that they all headed to what others call "the South Pole", to be far away from each other. They laugh at all of the airplanes heading in the wrong direction, flying to nowhere while running out of fuel.
--
Beware of correct answers to wrong questions.
John
http://www.pbase.com/image/55384958.jpg

 

[Michael Fryd]

Surely the original poster is sufficiently confused by now.

Probably not.

He's heard a number of explanations. All of which will allow him to get by with the basics.

• Subject lighting affects how much light is captured.
• Aperture affects how much light is captured, and depth of field.
• Shutter affects how much light is captured and motion blur.
• ISO affects how dark or light the resulting image looks (it sets up the relationship between light captured and how dark/light the JPEG looks).

It would be important for a beginner to know that in auto modes, the ISO setting changes the f-stop and/or the shutter speed, so it does affect the exposure and the noise.

All the beginner needs to know is that in Auto mode, the camera may adjust Aperture, shutter, ISO, or subject lighting (pop up flash).

... by moving along the path of an exposure triangle...

Pop up flash means moving to a different triangle.

But in any case, why is it important to confuse people with triangles that only include some factors?

Simply explain: In order to maintain the same image lightness, if you increase one factor by a stop, you need to decrease another factor by a stop. The factors are: subject lighting, aperture, shutter, and ISO. If you want to make the image lighter/darker, increase one factor without a corresponding decrease in another.

In what way does a triangle make that clearer?

The next step is to elaborate on how the photographer can choose to fix one or more of these variables, and allow the camera to adjust only the rest.

For instance, it is reasonable to show the beginner how to put the camera in Manual mode with Auto-ISO. This is a great way to teach with a digital camera.

The beginner can then play with aperture and shutter to see how they affect depth of field and, along with subject lighting, how the combination of the two affects image noise.

That's a great way of introducing the concepts that just wasn't possible with film. Which is why many who use a film based workflow don't think to use it.

The beauty of this is that this is a workflow that can be used on professional shoots. Set the wides aperture that yields sufficient depth of field. Use the slowest shutter that doesn't yield unwanted motion blur, and you are guaranteed the highest exposure (and therefore least noise) for the lighting conditions.

Teaching a beginner to use a fixed ISO tends to do them a disservice, unless they intend to be primarily shooting film.

"Fixed ISO" is not so fixed because you can adjust it.

In Aperture priority mode the photographer selects a "fixed" aperture, and the camera selects shutter and/or ISO.

But if you don't like the term "fixed", then substitute "Selected". For example "Teaching a beginner to Select a specific ISO tends to do them a disservice, unless they intend to be primarily shooting film."

The problem with what you advocate is that it is not so universal. Sometimes the light is so low, that you sacrifice the DOF, and change the idea of the shot to accommodate it. In low light, I would often put a fast prime, and that would make me shoot differently. Same with the shutter speed. When I shoot concerts, for example, I would go to slow speeds like 1/60 or even 1/30 sometimes, wait for the right moment, or take a few shots, hoping that some would be sharp enough. In other words, there is a balance you may want to achieve between noise, DOF, and motion blur, with some compromises in each one of them.

Absolutely, there are times when the photographer needs to have a good understanding of what the various factors do and how they interact. My suggestion is that it is better off to teach a beginner how to shoot in reasonable light, before we teach the techniques for dealing with challenging situations.

One of the reasons it's important to teach correct facts and terminology is that when you reach that point, it's easier to teach how to deal with challenging situations.

A good example of this is that some teach that a low exposure results in more noise, others teach that high ISO settings lead to more noise. While both may work for a beginner, only the former is correct. The issue is that someone who believes that the ISO setting is the cause of noise, might come to the conclusion that they can shoot raw, leave the ISO at 100, and then lighten the image in post processing. After all, at ISO 100 there shouldn't be any noise?

Also, in good light, I may decide that 1/125, f/8 is all I need and let the camera decide the ISO. The camera may very well compute ISO 25 then...

.

But of course, full auto (including Auto-ISO) is a great way to get a beginner started. One only needs to move to aperture or shutter priority (with Auto-ISO) once the beginner wants to start controlling depth of field or motion blur.

I did not mean exactly that. Fixed ISO and Av or TV are auto modes that are not "fully auto" like the green square.

The green square is only fully auto when you have selected Auto ISO. With s specific ISO selected it's still called "Full Auto" because that's what it was called on a film camera. Film cameras did not offer Auto-ISO.

 

[Bob A L]

The green square is only fully auto when you have selected Auto ISO. With s specific ISO selected it's still called "Full Auto" because that's what it was called on a film camera. Film cameras did not offer Auto-ISO.

I cannot speak for all cameras, but can guarantee you that the Nikon I have laying beside me at the minute most definitely gives the camera control of shutter speed, aperture and iso when set to the green fully auto setting on the dial. And I just checked a second Nikon Z camera and it also gave control of iso to the camera when the camera was set to the green auto (fully auto) position on the dial. On either of these two cameras you cannot change iso manually when in the green auto position. When in green auto exposure mode, they force the camera into auto iso mode. But these two cameras may be wrong all around though, because when in any semi auto exposure function when the operator changes any of the three (shutter speed, aperture, or iso) the camera will automatically change one or more of the settings it has control over verifying that it feels that all three of these functions work in harmony to achieve proper exposure of our photos.

 

[J A C S]

All the beginner needs to know is that in Auto mode, the camera may adjust Aperture, shutter, ISO, or subject lighting (pop up flash).

... by moving along the path of an exposure triangle...

Pop up flash means moving to a different triangle.

But in any case, why is it important to confuse people with triangles that only include some factors?

Simply explain: In order to maintain the same image lightness, if you increase one factor by a stop, you need to decrease another factor by a stop. The factors are: subject lighting, aperture, shutter, and ISO. If you want to make the image lighter/darker, increase one factor without a corresponding decrease in another.

In what way does a triangle make that clearer?

Did I say that it would make it clearer?

The next step is to elaborate on how the photographer can choose to fix one or more of these variables, and allow the camera to adjust only the rest.

For instance, it is reasonable to show the beginner how to put the camera in Manual mode with Auto-ISO. This is a great way to teach with a digital camera.

The beginner can then play with aperture and shutter to see how they affect depth of field and, along with subject lighting, how the combination of the two affects image noise.

That's a great way of introducing the concepts that just wasn't possible with film. Which is why many who use a film based workflow don't think to use it.

The beauty of this is that this is a workflow that can be used on professional shoots. Set the wides aperture that yields sufficient depth of field. Use the slowest shutter that doesn't yield unwanted motion blur, and you are guaranteed the highest exposure (and therefore least noise) for the lighting conditions.

Teaching a beginner to use a fixed ISO tends to do them a disservice, unless they intend to be primarily shooting film.

"Fixed ISO" is not so fixed because you can adjust it.

In Aperture priority mode the photographer selects a "fixed" aperture, and the camera selects shutter and/or ISO.

But if you don't like the term "fixed", then substitute "Selected". For example "Teaching a beginner to Select a specific ISO tends to do them a disservice, unless they intend to be primarily shooting film."

Then I must have been doing it wrong because this is the way I shoot almost all the time. I am pretty good with guessing a good ISO for the scene, and fixing the ISO in Av mode fixes the noise level. If I get an f-number and SS that I do not like, I would adjust the ISO - once only because I already got the data from my camera. I do not mind or care if other people do it differently, but it is definitely not wrong, even for a beginner.

The problem with what you advocate is that it is not so universal. Sometimes the light is so low, that you sacrifice the DOF, and change the idea of the shot to accommodate it. In low light, I would often put a fast prime, and that would make me shoot differently. Same with the shutter speed. When I shoot concerts, for example, I would go to slow speeds like 1/60 or even 1/30 sometimes, wait for the right moment, or take a few shots, hoping that some would be sharp enough. In other words, there is a balance you may want to achieve between noise, DOF, and motion blur, with some compromises in each one of them.

Absolutely, there are times when the photographer needs to have a good understanding of what the various factors do and how they interact. My suggestion is that it is better off to teach a beginner how to shoot in reasonable light, before we teach the techniques for dealing with challenging situations.

One of the reasons it's important to teach correct facts and terminology is that when you reach that point, it's easier to teach how to deal with challenging situations.

A good example of this is that some teach that a low exposure results in more noise, others teach that high ISO settings lead to more noise. While both may work for a beginner, only the former is correct. The issue is that someone who believes that the ISO setting is the cause of noise, might come to the conclusion that they can shoot raw, leave the ISO at 100, and then lighten the image in post processing. After all, at ISO 100 there shouldn't be any noise?

This is getting out of the Auto or semi-Auto settings.

Also, in good light, I may decide that 1/125, f/8 is all I need and let the camera decide the ISO. The camera may very well compute ISO 25 then...

.

But of course, full auto (including Auto-ISO) is a great way to get a beginner started. One only needs to move to aperture or shutter priority (with Auto-ISO) once the beginner wants to start controlling depth of field or motion blur.

I did not mean exactly that. Fixed ISO and Av or TV are auto modes that are not "fully auto" like the green square.

The green square is only fully auto when you have selected Auto ISO. With s specific ISO selected it's still called "Full Auto" because that's what it was called on a film camera. Film cameras did not offer Auto-ISO.

On my camera, the green square is a phone-like setting. Everything is auto. I never tried it though.

 

[Michael Fryd]

The green square is only fully auto when you have selected Auto ISO. With s specific ISO selected it's still called "Full Auto" because that's what it was called on a film camera. Film cameras did not offer Auto-ISO.

I cannot speak for all cameras, but can guarantee you that the Nikon I have laying beside me at the minute most definitely gives the camera control of shutter speed, aperture and iso when set to the green fully auto setting on the dial. And I just checked a second Nikon Z camera and it also gave control of iso to the camera when the camera was set to the green auto (fully auto) position on the dial. On either of these two cameras you cannot change iso manually when in the green auto position. When in green auto exposure mode, they force the camera into auto iso mode. But these two cameras may be wrong all around though, because when in any semi auto exposure function when the operator changes any of the three (shutter speed, aperture, or iso) the camera will automatically change one or more of the settings it has control over verifying that it feels that all three of these functions work in harmony to achieve proper exposure of our photos.

Canon DSLRs allow one to set a specific ISO when in the green square auto mode.

 

[Michael Fryd]

All the beginner needs to know is that in Auto mode, the camera may adjust Aperture, shutter, ISO, or subject lighting (pop up flash).

... by moving along the path of an exposure triangle...

Pop up flash means moving to a different triangle.

But in any case, why is it important to confuse people with triangles that only include some factors?

Simply explain: In order to maintain the same image lightness, if you increase one factor by a stop, you need to decrease another factor by a stop. The factors are: subject lighting, aperture, shutter, and ISO. If you want to make the image lighter/darker, increase one factor without a corresponding decrease in another.

In what way does a triangle make that clearer?

Did I say that it would make it clearer?

The next step is to elaborate on how the photographer can choose to fix one or more of these variables, and allow the camera to adjust only the rest.

For instance, it is reasonable to show the beginner how to put the camera in Manual mode with Auto-ISO. This is a great way to teach with a digital camera.

The beginner can then play with aperture and shutter to see how they affect depth of field and, along with subject lighting, how the combination of the two affects image noise.

That's a great way of introducing the concepts that just wasn't possible with film. Which is why many who use a film based workflow don't think to use it.

The beauty of this is that this is a workflow that can be used on professional shoots. Set the wides aperture that yields sufficient depth of field. Use the slowest shutter that doesn't yield unwanted motion blur, and you are guaranteed the highest exposure (and therefore least noise) for the lighting conditions.

Teaching a beginner to use a fixed ISO tends to do them a disservice, unless they intend to be primarily shooting film.

"Fixed ISO" is not so fixed because you can adjust it.

In Aperture priority mode the photographer selects a "fixed" aperture, and the camera selects shutter and/or ISO.

But if you don't like the term "fixed", then substitute "Selected". For example "Teaching a beginner to Select a specific ISO tends to do them a disservice, unless they intend to be primarily shooting film."

Then I must have been doing it wrong because this is the way I shoot almost all the time. I am pretty good with guessing a good ISO for the scene, and fixing the ISO in Av mode fixes the noise level. If I get an f-number and SS that I do not like, I would adjust the ISO - once only because I already got the data from my camera. I do not mind or care if other people do it differently, but it is definitely not wrong, even for a beginner.

Yes, one can guess at the ISO to use, and get good results. However that does not mean that guessing is better than Auto ISO. When the conditions can vary, Auto-ISO can often get you better results.

Suppose you are shooting indoors with available light. Perhaps you need f/5.6 for enough depth of field, and 1/60 to avoid motion blur. With these settings you get a good result at ISO 800. Based on this, you set the camera to ISO 800, and either shutter priority or aperture priority with the above settings.

Now, suppose you are moving around, and the room is not evenly lit. If you move to an area where there is one stop less light, the camera will either give you a slower shutter and unacceptable motion blur, or a wider aperture and not enough depth of field. If you had chosen a fixed f/5.6, 1/60 and Auto ISO, the camera would have simply chosen ISO 1600. You would have a slightly noisier. but useable image. Personally, I find it easier to address noise is post processing, than too shallow depth of field or too much motion blur.

But what if you move to area with one stop more light? With ISO 800 selected, the camera will either stop down, or use a faster shutter speed. This gives you more depth o field than you need, or more motion stopping than you need. However, of you had chosen a fixed f/5.6, 1/60 and Auto ISO, the camera would have simply chosen ISO 400, and you would have gotten a higher exposure, and less noise.

The bottom line is that selecting a particular ISO locks you into a particular exposure (and the associated noise level). Selecting aperture and shutter with Auto-ISO allows the exposure to vary with conditions, guaranteeing the highest exposure (and therefore lowest noise) for the situation.

Obviously, there are scenarios where you have to compromise on more than one factor, and this requires a little more input from the photographer.

The problem with what you advocate is that it is not so universal. Sometimes the light is so low, that you sacrifice the DOF, and change the idea of the shot to accommodate it. In low light, I would often put a fast prime, and that would make me shoot differently. Same with the shutter speed. When I shoot concerts, for example, I would go to slow speeds like 1/60 or even 1/30 sometimes, wait for the right moment, or take a few shots, hoping that some would be sharp enough. In other words, there is a balance you may want to achieve between noise, DOF, and motion blur, with some compromises in each one of them.

Absolutely, there are times when the photographer needs to have a good understanding of what the various factors do and how they interact. My suggestion is that it is better off to teach a beginner how to shoot in reasonable light, before we teach the techniques for dealing with challenging situations.

One of the reasons it's important to teach correct facts and terminology is that when you reach that point, it's easier to teach how to deal with challenging situations.

A good example of this is that some teach that a low exposure results in more noise, others teach that high ISO settings lead to more noise. While both may work for a beginner, only the former is correct. The issue is that someone who believes that the ISO setting is the cause of noise, might come to the conclusion that they can shoot raw, leave the ISO at 100, and then lighten the image in post processing. After all, at ISO 100 there shouldn't be any noise?

This is getting out of the Auto or semi-Auto settings.

Yes. I am not suggesting that one needs to discuss this with a beginner. I am suggesting that it is important to teach the beginner the correct explanation so that if they reach a point where they want to address a challenging situation, they have a good foundation and don't reach incorrect conclusions.

Also, in good light, I may decide that 1/125, f/8 is all I need and let the camera decide the ISO. The camera may very well compute ISO 25 then...

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But of course, full auto (including Auto-ISO) is a great way to get a beginner started. One only needs to move to aperture or shutter priority (with Auto-ISO) once the beginner wants to start controlling depth of field or motion blur.

I did not mean exactly that. Fixed ISO and Av or TV are auto modes that are not "fully auto" like the green square.

The green square is only fully auto when you have selected Auto ISO. With s specific ISO selected it's still called "Full Auto" because that's what it was called on a film camera. Film cameras did not offer Auto-ISO.

On my camera, the green square is a phone-like setting. Everything is auto. I never tried it though.

It seems this varies with camera brand.

 

[Bob A L]

How does it lock one into a specific iso or exposure, it's pretty simple on my cameras to see in the viewfinder if I need to raise or lower the iso for a particular shot. When I leave it in auto iso, it frequently makes decisions I am not happy with. I do put the camera my wife uses in auto iso or usually in green full auto as she wants no part of adjusting anything but focusing carefully.

 

[J A C S]

All the beginner needs to know is that in Auto mode, the camera may adjust Aperture, shutter, ISO, or subject lighting (pop up flash).

... by moving along the path of an exposure triangle...

Pop up flash means moving to a different triangle.

But in any case, why is it important to confuse people with triangles that only include some factors?

Simply explain: In order to maintain the same image lightness, if you increase one factor by a stop, you need to decrease another factor by a stop. The factors are: subject lighting, aperture, shutter, and ISO. If you want to make the image lighter/darker, increase one factor without a corresponding decrease in another.

In what way does a triangle make that clearer?

Did I say that it would make it clearer?

The next step is to elaborate on how the photographer can choose to fix one or more of these variables, and allow the camera to adjust only the rest.

For instance, it is reasonable to show the beginner how to put the camera in Manual mode with Auto-ISO. This is a great way to teach with a digital camera.

The beginner can then play with aperture and shutter to see how they affect depth of field and, along with subject lighting, how the combination of the two affects image noise.

That's a great way of introducing the concepts that just wasn't possible with film. Which is why many who use a film based workflow don't think to use it.

The beauty of this is that this is a workflow that can be used on professional shoots. Set the wides aperture that yields sufficient depth of field. Use the slowest shutter that doesn't yield unwanted motion blur, and you are guaranteed the highest exposure (and therefore least noise) for the lighting conditions.

Teaching a beginner to use a fixed ISO tends to do them a disservice, unless they intend to be primarily shooting film.

"Fixed ISO" is not so fixed because you can adjust it.

In Aperture priority mode the photographer selects a "fixed" aperture, and the camera selects shutter and/or ISO.

But if you don't like the term "fixed", then substitute "Selected". For example "Teaching a beginner to Select a specific ISO tends to do them a disservice, unless they intend to be primarily shooting film."

Then I must have been doing it wrong because this is the way I shoot almost all the time. I am pretty good with guessing a good ISO for the scene, and fixing the ISO in Av mode fixes the noise level. If I get an f-number and SS that I do not like, I would adjust the ISO - once only because I already got the data from my camera. I do not mind or care if other people do it differently, but it is definitely not wrong, even for a beginner.

Yes, one can guess at the ISO to use, and get good results. However that does not mean that guessing is better than Auto ISO. When the conditions can vary, Auto-ISO can often get you better results.

Suppose you are shooting indoors with available light. Perhaps you need f/5.6 for enough depth of field, and 1/60 to avoid motion blur. With these settings you get a good result at ISO 800. Based on this, you set the camera to ISO 800, and either shutter priority or aperture priority with the above settings.

Now, suppose you are moving around, and the room is not evenly lit. If you move to an area where there is one stop less light, the camera will either give you a slower shutter and unacceptable motion blur, or a wider aperture and not enough depth of field. If you had chosen a fixed f/5.6, 1/60 and Auto ISO, the camera would have simply chosen ISO 1600. You would have a slightly noisier. but useable image. Personally, I find it easier to address noise is post processing, than too shallow depth of field or too much motion blur.

Your premise is that I would want to stick with f/5.6, 1/60, no matter what. What I am trying to say is that I do not. I may go below that, as I explained before. I can risk it and allow 1/30 sec. I would get more blurry shots but some would be OK. If I reduce the light instead, all would be noisier. When I get to better light, I will be shooting with 1/60 or faster, thus minimizing the risk.

The advantage of shooting in Av mode with a fixed ISO (and I do not insist that everyone must use it) is that you have practically unlimited latitude of SS's available. Slow ones may introduce blur, so you have to watch it but there is no practical limit with the fast ones. ISO has a hard limit at ISO 100 (or 50, which is basically ISO 100), and a limit at high ISO as well, where you replace blur with noise.

Finally, in your example, you did not ignore the ISO completely. Why 1/60 instead of 1/250, for example, which is safer? Because you anticipate what the ISO would be.

But what if you move to area with one stop more light? With ISO 800 selected, the camera will either stop down, or use a faster shutter speed. This gives you more depth o field than you need, or more motion stopping than you need. However, of you had chosen a fixed f/5.6, 1/60 and Auto ISO, the camera would have simply chosen ISO 400, and you would have gotten a higher exposure, and less noise.

The bottom line is that selecting a particular ISO locks you into a particular exposure (and the associated noise level). Selecting aperture and shutter with Auto-ISO allows the exposure to vary with conditions, guaranteeing the highest exposure (and therefore lowest noise) for the situation.

Obviously, there are scenarios where you have to compromise on more than one factor, and this requires a little more input from the photographer.