Help with Shutter, aperture, and iso?

[Advanced Photo]

Doesn't ISO in digital just increase the gamma? That's how it seems anyways.

 

[john.margetts]

It's a nice video but the information is wrong and misleading. At 4:10 in the video they say this: "The higher the ISO the more sensitive the sensor is to light." That's just plain false. The light sensitivity of a digital sensor is fixed in manufacturer and can not be increased or decreased. Digital camera sensors do not get more sensitive to light when you change ISO.

Joe

while you are correct you are on a hiding to nothing if you want most people to listen to you. The camera manuals tell us sensor sensitivity increases, all those YouTube videos tells us the same as do these internet forums.

 

[Advanced Photo]

It's a nice video but the information is wrong and misleading. At 4:10 in the video they say this: "The higher the ISO the more sensitive the sensor is to light." That's just plain false. The light sensitivity of a digital sensor is fixed in manufacturer and can not be increased or decreased. Digital camera sensors do not get more sensitive to light when you change ISO.

Joe

while you are correct you are on a hiding to nothing if you want most people to listen to you. The camera manuals tell us sensor sensitivity increases, all those YouTube videos tells us the same as do these internet forums.

If only it were true, one could buy sensors that are not very sensitive to light put it in a camera, turn up the ISO and remove the now more sensitive sensor, sell it at a profit since it's now more sensitive, and repeat until you are wealthy enough to retire.

Awesome.

 

[robbins.photo]

while you are correct you are on a hiding to nothing if you want most people to listen to you. The camera manuals tell us sensor sensitivity increases, all those YouTube videos tells us the same as do these internet forums.

Well sure, but then you can't pick out some incredibly esoteric argument based mostly on semantics to prove your amazing level of knowledge. Granted, most novices would give a crap less about this incredibly subtle difference, and it really has no bearing on the end results. But that's not really the point now is it?

 

[Ysarex]

Doesn't ISO in digital just increase the gamma? That's how it seems anyways.

It depends on how the camera is designed. The sensor generates an analog signal -- electrical voltage. That analog signal is taken by the camera's ADC (analog to digital converter) and transformed into digital data (numbers). In some cameras (Sigma, some Nikon APS models) nothing is done between these two steps 1. expose and generate signal and 2. convert signal to digital data. In the case of this design all brightening of the image to compensate for reduced exposure is done with the already converted digital data -- common term for this is up scaling the data. In another design (Canon) the analog signal is preprocessed prior to ADC conversion. It's boosted to compensate for the underexposure and then converted to numbers. In yet another design (Fuji) a hybrid combination of the two processes is used. Gamma is not altered by these processes. Digital up scaling and/or the pre ADC signal boost are both linearly applied.

Joe

 

[TCampbell]

Technically increasing the ISO results in an amplification of signal. Exactly "how" the signal gets amplified varies by chip.

But if you could count the exact number of photons that land on the chip at some given ISO, shutter speed, and aperture... then change nothing but ISO and take another shot, the number of photons that land on the chip is "theoretically" the same (given this is a quantum measurement so things like quantum uncertainty come into play).

That means if you took an image at ISO 100, imported it into some software such as Lightroom, told the software to increase the exposure by one stop, then you'd get the same result as if you simply told the camera to shot the same image at ISO 200. Again... there will be differences between how Lightroom applies 1 stop of signal amplification and how the camera's internal compoenents add 1 stop of signal amplification, but they are roughly doing the same thing.

But it's usually easier to tell people that you can think of it "as if" the camera is becoming more sensitive to light.

 

[Advanced Photo]

ISO being a measure of film sensitivity and the name only was carried over to digital is still thought of the same way even though it is a digital method of reproducing a similar effect and not an actual ISO rating for the sensor.

 

[Ysarex]

ISO being a measure of film sensitivity and the name only was carried over to digital is still thought of the same way even though it is a digital method of reproducing a similar effect and not an actual ISO rating for the sensor.

With the introduction of digital cameras the ISO spec was re-written and very interestingly allows the camera manufacturer to chose between some variations in how ISO is determined for their cameras. This has led to some angst in places like these forums when a photog with two different brand cameras has put them down side by side and discovered that at the same ISO values the cameras select different exposure settings. Somebody must be cheating!

One option to determine ISO which is preferred by DxOMark is sensor saturation (my personal favorite). In this method ISO is determined for the sensor and based on the sensor's exposure threshold -- clipping point reached. This is a hard measure. Another option is to determine ISO based on the JPEG output of the camera image processor -- a soft measure (most camera manufacturer's favorite).

ISO for film is not a fully appropriate analogy for digital cameras. Everyone focuses on the grain/noise correlation; increase ISO and both film grain and digital noise both increase. Well there's more going on than that. When you increase ISO for a digital camera you also reduce the dynamic range capacity of the sensor. Typically when you increase ISO using film you also increase the dynamic range capacity of the film -- opposite digital.

The better analogy is pushing film. When you didn't bring a higher ISO film with you, you can underexpose the film you have and then compensate in development by increasing development time. The film gets grainier and the shadow detail drops out but the increased development gives you normal density film.

Joe

 

[Ysarex]

It's a nice video but the information is wrong and misleading. At 4:10 in the video they say this: "The higher the ISO the more sensitive the sensor is to light." That's just plain false. The light sensitivity of a digital sensor is fixed in manufacturer and can not be increased or decreased. Digital camera sensors do not get more sensitive to light when you change ISO.

Joe

while you are correct you are on a hiding to nothing if you want most people to listen to you. The camera manuals tell us sensor sensitivity increases, all those YouTube videos tells us the same as do these internet forums.

I know, I said as much in a previous post. I frequently ignore this and other similar stuff -- something must have made me grumpy today I do get tired of the constant flow of it into my classroom. Me: "What?! Where'd you hear that?" Brad: "Youtube." Me: "Hang on a minute, I have to bang my head on the desk."

Joe

 

[Advanced Photo]

lol The digital techs took the S out of ISO. There are no longer any standards to guide the industry.

 

[Ysarex]

lol The digital techs took the S out of ISO. There are no longer any standards to guide the industry.

Here's a quick informative read in an article by Richard Butler: Sense and Sensitivity

Here's the salient juicy stuff:
"However, the standard set down by the International Organization for Standardization (ISO12232:2006, as it happens), contains five separate definitions, each of which can produce a different answer for the same camera. Thankfully, only three of these definitions are widely used and only two, closely-related definitions are used by camera makers.

ISO, courtesy of CIPA
The two definitions of ISO that are actually used by camera manufacturers (and are reported by their cameras) are based on the brightness of cameras' JPEG output. Both definitions come from standards developed by the Japanese camera trade body CIPA, which were adopted by ISO in 2006."

Basically the International Organization for Standardization allowed the Japanese camera manufacturers to write it for them.

The fact is the sensor in your camera is light sensitive. It is a piece of hardware and it can be user tested. You want to know what the exposure limits of your camera sensor are get this: Raw Digger. I test all my hardware and I don't give a bleep what Fuji or Nikon or Canon think my photos should look like.

Joe

 

[photo1x1.com]

Hi guys,
you two are definitely right on the information you give. May I just throw in the experience I have with many people new to DSLR, or photography in general. People that do not know anything about aperture, shutter speed and iso usually are overwhelmed by too much in depth knowledge. I am a techy myself and love all the scientific background. But I have seen beginners that even gave up due to everything being way too complicated, while in fact it is not complicated at all, if you start out the easy way.
For most people that is all information they may ever need, because the percentage of people that go professional is pretty small, and those can learn the science part of it later in their career.
Hand held light meters are awesome, but people who hesitate to buy a 50mm 1.8 for $125 will hardly be interested in the cheapest Sekonic for $126, especially since that would totally swamp them, if they don´t even know hot to set manual exposure, or even use aperture priority.

I´m pretty new here in the forum, and you two are honourable long term members. While I don´t really feel entitled to raise my concern, I still think I need to humbly throw that into the discussion. What do you think?

I think it's a legitimate question/point and a tricky problem. Basically it boils down to where to draw the line between giving a beginner useful info and encouragement and not giving them too much or any false info because it's too complicated to explain how it really works. A simpler photo example: We can count on the fact that some budding enthusiast will be along here soon enough wanting to know why they saw someone using a 35mm lens on an m4/3 camera to shoot a portrait when they had learned that a 35mm lens distorts too much to use for portraits. Originally they were probably given the easy explanation and wound up linking focal length and perspective such that they now believe perspective (and distortion) is a function of the focal length/lens and goes wherever the lens goes. Now they're confused and have to re-learn. In the meantime they've spread the fallacy to a dozen of their friends who proceeded to do the same. (So I already know I'm not going to win this one).

Even Nikon in their camera manuals describes ISO as determining the sensitivity of the camera and that raising ISO increases sensitivity. (I'm really not going to win this one). But of course that's not true. It's also not true that raising the ISO value on a digital camera makes the photo noisy or noisier. In fact it does the opposite and typically reduces the noise that is caused by underexposure. Neither is ISO a direct determinant of exposure. A correct definition of photographic exposure does not include ISO. So when we "exposure triangle" a bunch of new photographers we plant misleading ideas in their heads.

In argument for: the exposure triangle model is pretty simple and can get them up and functioning quickly with a minimum of pain. But shouldn't we at least assume and respect their intelligence and tell them, "look this model will help you quick start, but it's actually a bad fit to what's really going on." Bet you most of them would immediately ask you to tell them what's really going on.

A story: I'm a retired college prof who still does some part-time teaching. Right now I have a student in my class who is younger than me and also teaching photography. She was encouraged to sit-in my class because I was recommended as a source to help understand color management. A couple weeks ago when ISO came up in class I took the time to explain it. I noticed a look of astonishment on her face (she shoots Nikon -- note comment above). Then she says to me, "so changing ISO on a digital camera isn't the same as changing film. It's really more like pushing film isn't it?" And I said, "Exactly right. You can't change the sensitivity of the sensor but you can 'underexpose it and then overdevelop.' And what always happened to the shadow detail when you pushed film?" And she excitedly says, "OMG! it all finally makes sense. Why didn't they just tell me in the first place?" Now what was the point of keeping her in a fog? She's passing this nonsense on to her students and you can't blame her it's right there in her Nikon camera manual and probably in the textbook she uses.

There's a problem if the explanation you provide for something doesn't make logical sense when you try and think about it carefully. People end up confused. If they are interested in learning more their further learning is retard by the fog they've been placed in and the misdirection they been given. Most photographers out there in fact believe they can increase the light sensitivity of digital cameras by raising the ISO value. Should we really continue to perpetuate that and so many other fallacies?

Joe

P.S. I watched your youtube videos and applaud you for resisting the standard "ISO increases sensitivity" rubbish. Your megaphone and amplifier sliders did a good job of getting across how it really works and you used the term "increase brightness" which is a whole lot more accurate than saying exposure. ISO in a digital camera really is a post processing step that occurs after exposure. Your videos are much better than the average fare in that regard, so you're smart enough to make an adjustment that also gives them an accurate understanding of exposure: luminance + shutter speed + aperture.

First of all - thanks for checking my videos and giving me your highly valued feedback (and I mean it like that ).
In regard to your suggestion of using Luminance + Shutter Speed + Aperture: I am totally with you and I plan adding luminance in a later movie. For these intros to photography, I still think it is better to keep the three most prominent, to get people started, because these are values, that people can "change" in camera. Getting people started in my opinion is the most important part, because that keeps their interest. Some people are like the student in your class who want to know all the details. I guess the relative amount of people interested in the science part of photography that visit your class in relation to the average guy or girl with a DSLR interested in photography science is much, much higher. For these average people, it is important to have quick success to keep them motivated. Some will be happy with that, but others won´t and they keep reading/watching youtube, etc.. In my videos I try to satisfy both - starting as easy as possible, without telling them anything wrong. If I do use simplifications, I usually tell them "we´ll get to that in a later movie" and show a screengrab of these videos (even though many of these are not online yet - unfortunately youtube doesn´t give you an option to update movies, so I have to have an exact idea and structure for future videos). Later I´ll upload in depth scientific information about various topics. But it takes time.

As for your focal length example with 35mm. In my experience there is no perfect focal length that fits everybody equally. It depends on the proportions of peoples faces (plus their parts) and bodies what fits them best. But I don´t want to tear this thread further off topic.
There is a fine line between arising peoples interest for more in depth knowledge and overwhelming them with too much information. That line is different for every single person. In a one to one course you can individually respond to a persons mental skills, in your classes you can still address people differently, but in books, videos and forums you can´t really. So I´d rather recommend some well written books, well structured videos and workshops/classes, than try to put a lot of science into a pretty short forum post.

In the end it seems the OP has left the forum which I see a little as proofing my point of not trying to overwhelm newbies with too much info. First of all I hope I´m wrong, and he will eventually turn up again, and if not, I hope he just lost the forum and didn´t lose interest in serious photography all together. And yes, I know I contributed to this thread drifting pretty much, sorry .

One thing I really love about this forum: I have yet to find a topic where people say: "use the search function". Even basic questions like the ones in the OP are answered without being rude, even though this one ends up in a long winding discussion. That´s something that can hardly be found elsewhere. AND: I think it is important because it means helping a beginner on a one to one basis. If he finds he has additional questions, he can raise it in his own topic - not possible using the search function. So: great job! Hats off to all of you long term members!

 

[KmH]

lol The digital techs took the S out of ISO. There are no longer any standards to guide the industry.

Digital ISO standards:
Film speed - Wikipedia

 

[Ysarex]

Hi guys,
you two are definitely right on the information you give. May I just throw in the experience I have with many people new to DSLR, or photography in general. People that do not know anything about aperture, shutter speed and iso usually are overwhelmed by too much in depth knowledge. I am a techy myself and love all the scientific background. But I have seen beginners that even gave up due to everything being way too complicated, while in fact it is not complicated at all, if you start out the easy way.
For most people that is all information they may ever need, because the percentage of people that go professional is pretty small, and those can learn the science part of it later in their career.
Hand held light meters are awesome, but people who hesitate to buy a 50mm 1.8 for $125 will hardly be interested in the cheapest Sekonic for $126, especially since that would totally swamp them, if they don´t even know hot to set manual exposure, or even use aperture priority.

I´m pretty new here in the forum, and you two are honourable long term members. While I don´t really feel entitled to raise my concern, I still think I need to humbly throw that into the discussion. What do you think?

I think it's a legitimate question/point and a tricky problem. Basically it boils down to where to draw the line between giving a beginner useful info and encouragement and not giving them too much or any false info because it's too complicated to explain how it really works. A simpler photo example: We can count on the fact that some budding enthusiast will be along here soon enough wanting to know why they saw someone using a 35mm lens on an m4/3 camera to shoot a portrait when they had learned that a 35mm lens distorts too much to use for portraits. Originally they were probably given the easy explanation and wound up linking focal length and perspective such that they now believe perspective (and distortion) is a function of the focal length/lens and goes wherever the lens goes. Now they're confused and have to re-learn. In the meantime they've spread the fallacy to a dozen of their friends who proceeded to do the same. (So I already know I'm not going to win this one).

Even Nikon in their camera manuals describes ISO as determining the sensitivity of the camera and that raising ISO increases sensitivity. (I'm really not going to win this one). But of course that's not true. It's also not true that raising the ISO value on a digital camera makes the photo noisy or noisier. In fact it does the opposite and typically reduces the noise that is caused by underexposure. Neither is ISO a direct determinant of exposure. A correct definition of photographic exposure does not include ISO. So when we "exposure triangle" a bunch of new photographers we plant misleading ideas in their heads.

In argument for: the exposure triangle model is pretty simple and can get them up and functioning quickly with a minimum of pain. But shouldn't we at least assume and respect their intelligence and tell them, "look this model will help you quick start, but it's actually a bad fit to what's really going on." Bet you most of them would immediately ask you to tell them what's really going on.

A story: I'm a retired college prof who still does some part-time teaching. Right now I have a student in my class who is younger than me and also teaching photography. She was encouraged to sit-in my class because I was recommended as a source to help understand color management. A couple weeks ago when ISO came up in class I took the time to explain it. I noticed a look of astonishment on her face (she shoots Nikon -- note comment above). Then she says to me, "so changing ISO on a digital camera isn't the same as changing film. It's really more like pushing film isn't it?" And I said, "Exactly right. You can't change the sensitivity of the sensor but you can 'underexpose it and then overdevelop.' And what always happened to the shadow detail when you pushed film?" And she excitedly says, "OMG! it all finally makes sense. Why didn't they just tell me in the first place?" Now what was the point of keeping her in a fog? She's passing this nonsense on to her students and you can't blame her it's right there in her Nikon camera manual and probably in the textbook she uses.

There's a problem if the explanation you provide for something doesn't make logical sense when you try and think about it carefully. People end up confused. If they are interested in learning more their further learning is retard by the fog they've been placed in and the misdirection they been given. Most photographers out there in fact believe they can increase the light sensitivity of digital cameras by raising the ISO value. Should we really continue to perpetuate that and so many other fallacies?

Joe

P.S. I watched your youtube videos and applaud you for resisting the standard "ISO increases sensitivity" rubbish. Your megaphone and amplifier sliders did a good job of getting across how it really works and you used the term "increase brightness" which is a whole lot more accurate than saying exposure. ISO in a digital camera really is a post processing step that occurs after exposure. Your videos are much better than the average fare in that regard, so you're smart enough to make an adjustment that also gives them an accurate understanding of exposure: luminance + shutter speed + aperture.

First of all - thanks for checking my videos and giving me your highly valued feedback (and I mean it like that ).
In regard to your suggestion of using Luminance + Shutter Speed + Aperture: I am totally with you and I plan adding luminance in a later movie. For these intros to photography, I still think it is better to keep the three most prominent, to get people started, because these are values, that people can "change" in camera. Getting people started in my opinion is the most important part, because that keeps their interest. Some people are like the student in your class who want to know all the details. I guess the relative amount of people interested in the science part of photography that visit your class in relation to the average guy or girl with a DSLR interested in photography science is much, much higher. For these average people, it is important to have quick success to keep them motivated. Some will be happy with that, but others won´t and they keep reading/watching youtube, etc.. In my videos I try to satisfy both - starting as easy as possible, without telling them anything wrong.

There's the problem: You are telling them something wrong. And I'm not advocating that we shouldn't make it simple and short and fun and accessible. I'm just suggesting it would be best if we can avoid telling them anything wrong.

From Ilford's The Manual of Photography (page 231):
"Exposure
When a photograph is taken, light from the various areas of the subject falls on corresponding areas of the film for a set time. The effect produced on the emulsion is, within limits, proportional to the product of the illuminance E and the exposure time t. We express this by the equation H = Et"

From webopedia What is exposure? Webopedia Definition :
"exposure
By Vangie Beal In digital photography, exposure is the unit of measurement for the total amount of light permitted to reach the electronic sensor during the process of taking a photograph. The two main controls your digital camera uses to control exposure are the shutter speed and aperture."

From Wikipedia Exposure (photography) - Wikipedia :
"In photography, exposure is the amount of light per unit area (the image plane illuminance times the exposure time) reaching a photographic film or electronic image sensor, as determined by shutter speed, lens aperture and scene luminance."

OK, so Ilford and web encyclopedias are in basic agreement.

Now I've watched your videos and I'm confused. Can you answer my question please: I set my camera up to photograph a scene with constant illumination. I set the shutter speed to X and the f/stop to Y and I make an exposure. Your videos are telling me that "ISO is the third component that defines the exposure" so now I'm going to change the ISO value on the camera to a higher value and trip the shutter again (same constant illumination, same shutter X and same f/stop Y).

Is that 2nd exposure different than the 1st exposure? (Yes/No). Can you explain how changing the ISO value altered the 2nd exposure so that more or less light reached the sensor -- how does that work?

Yeah I know, when you use the term "exposure" in your videos you don't really mean exposure you mean something else. And you're in good company with Bryan Petersen (Misunderstanding Exposure) and the huge army of Youtube triangulites. But there is no way in which ISO defines exposure and to say so is to say something wrong. I think it's better if we don't do that.

Joe

 

[photo1x1.com]

Hi guys,
you two are definitely right on the information you give. May I just throw in the experience I have with many people new to DSLR, or photography in general. People that do not know anything about aperture, shutter speed and iso usually are overwhelmed by too much in depth knowledge. I am a techy myself and love all the scientific background. But I have seen beginners that even gave up due to everything being way too complicated, while in fact it is not complicated at all, if you start out the easy way.
For most people that is all information they may ever need, because the percentage of people that go professional is pretty small, and those can learn the science part of it later in their career.
Hand held light meters are awesome, but people who hesitate to buy a 50mm 1.8 for $125 will hardly be interested in the cheapest Sekonic for $126, especially since that would totally swamp them, if they don´t even know hot to set manual exposure, or even use aperture priority.

I´m pretty new here in the forum, and you two are honourable long term members. While I don´t really feel entitled to raise my concern, I still think I need to humbly throw that into the discussion. What do you think?

I think it's a legitimate question/point and a tricky problem. Basically it boils down to where to draw the line between giving a beginner useful info and encouragement and not giving them too much or any false info because it's too complicated to explain how it really works. A simpler photo example: We can count on the fact that some budding enthusiast will be along here soon enough wanting to know why they saw someone using a 35mm lens on an m4/3 camera to shoot a portrait when they had learned that a 35mm lens distorts too much to use for portraits. Originally they were probably given the easy explanation and wound up linking focal length and perspective such that they now believe perspective (and distortion) is a function of the focal length/lens and goes wherever the lens goes. Now they're confused and have to re-learn. In the meantime they've spread the fallacy to a dozen of their friends who proceeded to do the same. (So I already know I'm not going to win this one).

Even Nikon in their camera manuals describes ISO as determining the sensitivity of the camera and that raising ISO increases sensitivity. (I'm really not going to win this one). But of course that's not true. It's also not true that raising the ISO value on a digital camera makes the photo noisy or noisier. In fact it does the opposite and typically reduces the noise that is caused by underexposure. Neither is ISO a direct determinant of exposure. A correct definition of photographic exposure does not include ISO. So when we "exposure triangle" a bunch of new photographers we plant misleading ideas in their heads.

In argument for: the exposure triangle model is pretty simple and can get them up and functioning quickly with a minimum of pain. But shouldn't we at least assume and respect their intelligence and tell them, "look this model will help you quick start, but it's actually a bad fit to what's really going on." Bet you most of them would immediately ask you to tell them what's really going on.

A story: I'm a retired college prof who still does some part-time teaching. Right now I have a student in my class who is younger than me and also teaching photography. She was encouraged to sit-in my class because I was recommended as a source to help understand color management. A couple weeks ago when ISO came up in class I took the time to explain it. I noticed a look of astonishment on her face (she shoots Nikon -- note comment above). Then she says to me, "so changing ISO on a digital camera isn't the same as changing film. It's really more like pushing film isn't it?" And I said, "Exactly right. You can't change the sensitivity of the sensor but you can 'underexpose it and then overdevelop.' And what always happened to the shadow detail when you pushed film?" And she excitedly says, "OMG! it all finally makes sense. Why didn't they just tell me in the first place?" Now what was the point of keeping her in a fog? She's passing this nonsense on to her students and you can't blame her it's right there in her Nikon camera manual and probably in the textbook she uses.

There's a problem if the explanation you provide for something doesn't make logical sense when you try and think about it carefully. People end up confused. If they are interested in learning more their further learning is retard by the fog they've been placed in and the misdirection they been given. Most photographers out there in fact believe they can increase the light sensitivity of digital cameras by raising the ISO value. Should we really continue to perpetuate that and so many other fallacies?

Joe

P.S. I watched your youtube videos and applaud you for resisting the standard "ISO increases sensitivity" rubbish. Your megaphone and amplifier sliders did a good job of getting across how it really works and you used the term "increase brightness" which is a whole lot more accurate than saying exposure. ISO in a digital camera really is a post processing step that occurs after exposure. Your videos are much better than the average fare in that regard, so you're smart enough to make an adjustment that also gives them an accurate understanding of exposure: luminance + shutter speed + aperture.

First of all - thanks for checking my videos and giving me your highly valued feedback (and I mean it like that ).
In regard to your suggestion of using Luminance + Shutter Speed + Aperture: I am totally with you and I plan adding luminance in a later movie. For these intros to photography, I still think it is better to keep the three most prominent, to get people started, because these are values, that people can "change" in camera. Getting people started in my opinion is the most important part, because that keeps their interest. Some people are like the student in your class who want to know all the details. I guess the relative amount of people interested in the science part of photography that visit your class in relation to the average guy or girl with a DSLR interested in photography science is much, much higher. For these average people, it is important to have quick success to keep them motivated. Some will be happy with that, but others won´t and they keep reading/watching youtube, etc.. In my videos I try to satisfy both - starting as easy as possible, without telling them anything wrong.

There's the problem: You are telling them something wrong. And I'm not advocating that we shouldn't make it simple and short and fun and accessible. I'm just suggesting it would be best if we can avoid telling them anything wrong.

From Ilford's The Manual of Photography (page 231):
"Exposure
When a photograph is taken, light from the various areas of the subject falls on corresponding areas of the film for a set time. The effect produced on the emulsion is, within limits, proportional to the product of the illuminance E and the exposure time t. We express this by the equation H = Et"

From webopedia What is exposure? Webopedia Definition :
"exposure
By Vangie Beal In digital photography, exposure is the unit of measurement for the total amount of light permitted to reach the electronic sensor during the process of taking a photograph. The two main controls your digital camera uses to control exposure are the shutter speed and aperture."

From Wikipedia Exposure (photography) - Wikipedia :
"In photography, exposure is the amount of light per unit area (the image plane illuminance times the exposure time) reaching a photographic film or electronic image sensor, as determined by shutter speed, lens aperture and scene luminance."

OK, so Ilford and web encyclopedias are in basic agreement.

Now I've watched your videos and I'm confused. Can you answer my question please: I set my camera up to photograph a scene with constant illumination. I set the shutter speed to X and the f/stop to Y and I make an exposure. Your videos are telling me that "ISO is the third component that defines the exposure" so now I'm going to change the ISO value on the camera to a higher value and trip the shutter again (same constant illumination, same shutter X and same f/stop Y).

Is that 2nd exposure different than the 1st exposure? (Yes/No). Can you explain how changing the ISO value altered the 2nd exposure so that more or less light reached the sensor -- how does that work?

Yeah I know, when you use the term "exposure" in your videos you don't really mean exposure you mean something else. And you're in good company with Bryan Petersen (Misunderstanding Exposure) and the huge army of Youtube triangulites. But there is no way in which ISO defines exposure and to say so is to say something wrong. I think it's better if we don't do that.

Joe

I agree with you and I thought a lot about that in the last two days. What I could have done was to avoid the term "exposure" all together, and use image brightness only. I need to think about that. Unfortunately as I said earlier, youtube won´t let me change a video that is already online. So I need to think whether I start all over, or live with a (I would still call it small - but I know you´ll disagree) incorrectness that is pretty common. I don´t think it will make a difference for 99.99% of all the people with a camera.
There are so many other similar common misconceptions out there, and while I´m not a fan of contributing to that, I need to decide whether it does make a real difference to the majority of my viewers, or rather not.
Anyway - thanks a lot for your time and patience .