Exposure?

I understand the three elements of managing light, iso, apeture and shutter speed. If we set these three correctly, why do we need a fourth element, 'exposure'?

Bertam,

Could you provide a link where you got your information from? If not, then use this link as it will provide you with your answers.

https://www.cambridgeincolour.com/tu...a-exposure.htm

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Originally Posted by bertam

I understand the three elements of managing light, iso, apeture and shutter speed. If we set these three correctly, why do we need a fourth element, 'exposure'?

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Those are the three factors which make up exposure. I'm not sure what you mean by the fourth element being exposure.

If someone were to say "that exposure needs to be a bit brighter" you would alter one of the factors to brighten the image. Increase the shutter speed, increase ISO, open the aperture a bit, or some combination of the three.

Exposure is the input to the camera's sensor when taking the photograph - the amount of light that reaches the sensor, which depends upon the luminance of the scene, the size of the lens aperture, and the exposure time (i.e. shutter speed). The ISO value is an amplification factor applied to the output from the sensor, to brighten the resultant image to a level acceptable to the viewer - this can be applied in-camera or in post-processing.

Cheers.
Philip

I think of EV as a way to adjust exposure too. 1EV = one stop is my rule of thumb.

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Originally Posted by MrB

Exposure is the input to the camera's sensor when taking the photograph - the amount of light that reaches the sensor, which depends upon the luminance of the scene, the size of the lens aperture, and the exposure time (i.e. shutter speed). The ISO value is an amplification factor applied to the output from the sensor, to brighten the resultant image to a level acceptable to the viewer - this can be applied in-camera or in post-processing.

Cheers.
Philip

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Exactly. It's confusing, because people (including me) talk about ISO, shutter speed, and aperture as the "exposure triangle." They do that because in terms of the brightness of the resulting image, any one of the three can compensate for any of the other two. You can compensate for halving the shutter speed, for example, either by opening the aperture one stop or by doubling ISO. But at least traditionally, exposure means how much you have exposed the sensor to light, which is determined entirely by aperture and shutter speed. In the days of film, no one would have referred to choosing a higher-ISO (ASA in my film day) as increasing exposure.

As Philip wrote, increasing ISO simply amplifies the signal generated by the sensor. While it can be done either in camera or in post, with some cameras, the results are not always identical.

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Originally Posted by bertam

I understand the three elements of managing light, iso, apeture and shutter speed. If we set these three correctly, why do we need a fourth element, 'exposure'?

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as has been said, Bertram, these three things make up the exposure triangle. So, to slightly amend your own question and turn it into a statement:-

I understand the three elements of managing light, iso, apeture and shutter speed. If we set these three correctly, then we will have a good 'exposure'.

I do not disagree with any of the above replies, but (to be pedantic/thorough) there is a fourth variable - the amount of light, which it may be possible to increase; e.g.
a) if shooting still life indoors by window light, open the curtains/drapes/blinds more, or take down the net curtains - this latter is probably a UK phenomena only :)
b) if shooting by flash (or continuous artificial light), increase the power and/or move it closer to the subject

Of course, if the exposure problem was caused by the subject being too bright, reverse all the logic of my suggestions.

Cheers, Dave

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Originally Posted by Dave Humphries

I do not disagree with any of the above replies, but (to be pedantic/thorough) there is a fourth variable - the amount of light, which it may be possible to increase; e.g.
a) if shooting still life indoors by window light, open the curtains/drapes/blinds more, or take down the net curtains - this latter is probably a UK phenomena only :)
b) if shooting by flash (or continuous artificial light), increase the power and/or move it closer to the subject

Of course, if the exposure problem was caused by the subject being too bright, reverse all the logic of my suggestions.

Cheers, Dave

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So there is in a sense only one element (light), the sensor is the medium used to capture the moment in time, and the triangle (ISO, shutterspeed, aperture) are the variables used to present that moment in the way we either see or want to see. Of course there are other elements (air, water, heat, and perhaps dust particles) that could make or break our attempts.

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Originally Posted by Dave Humphries

I do not disagree with any of the above replies, but (to be pedantic/thorough) there is a fourth variable -

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But I think that for Bertram, at this stage of his learning, he should just think in terms of the three elements that make up the exposure triangle. I think his question is about those three elements working, no matter what light is available. Even if you do introduce moire light, you still need to understand and get the settings for those three elements correct.

Once the relationship between these is well understood, we can start thinking about the more nuanced and advanced concepts such as that introduced by Dave.

I agree with Donald that the aspect of introducing the idea of changing the light falling on the scene adds complexity to the answer that was not implied by the understandably simple nature of the question. Perhaps most important, we shouldn't explain changing the amount of light falling on the scene without also discussing how doing so will usually change not just the brightness of the light but also other characteristics of the light and scene. That then introduces yet more complexity that, again, seems not to have been implied in the simple question.

I saw a tutorial where the tutor set the 'three elements' then he looked at the screen and said it was too dark. He then adjusted a dial (which I thought was an exposure adjustment) which enabled him to lighten or darken the image to his requirements. Is this not exposure?

Bertam,
The explanations provided already, have hopefully answered your question.

But it may also help to think of 'Exposure' in terms of the final image and whether it is: -

'Overexposed' ie when the combination of aperture, ISO and shutter speed result in a loss of highlight detail so that important bright parts of the image are "washed out".

or,

'Underexposed' ie when the combination of aperture, ISO and shutter speed result in a loss of important shadow detail.

When the balance between these two conditions is right you achieve 'correct' exposure.

The point is that you can create this balance from different combinations of ISO, aperture and shutter speed.

Bertram - let me just add another layer to the explanation you have received. From a technical standpoint, this information is 100% correct. Your will get a correctly exposed image by balancing these three parameters, but depending on the combination of the ones you choose, can get your three totally different looking images.

Some camera modes let the camera choose these values for you automatically, and while that will generally give you a decent image that is properly exposed. You are the person looking at the scene and are best placed to make these choices, not some engineer sitting somewhere (usually in Japan) who is designing the algorithms to make these choices for you. All of these parameters will impact the composition and quality of your image, so understanding the tradeoffs is just as important as framing your shot.

1. ISO setting - your camera's base ISO usually gives you the best image quality. The camera typically has the least amount of digital noise, has the highest colour depth (the number of individual colour shades it can record) and highest dynamic range (the largest range of getting details in the dark shadow areas as well as highlight detail in the brightest areas). I will try to shoot at base ISO when ever I can, and if i can't I will shot at as low an ISO setting as possible.

2. Aperture - this controls the area of the image that is in focus. A large aperture (i.e. low aperture number) will give you a very shallow "in focus area". A narrow aperture (i.e. larger aperture number) will give you an image where much and potentially all of the image is in focus.

3. Shutter speed - a high shutter speed will freeze motion, whereas a low shutter speed will tend to blur movement.

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Originally Posted by bertam

I saw a tutorial where the tutor set the 'three elements' then he looked at the screen and said it was too dark. He then adjusted a dial (which I thought was an exposure adjustment) which enabled him to lighten or darken the image to his requirements. Is this not exposure?

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I do not know what that was, Bertram. When you say he adjusted a dial, was this on the camera? If so, do you know what camera it was the tutor was using.

There may be a camera that does have a dial to adjust 'exposure'. BUT if there is then what it is doing is making an adjustment to either the shutter speed, Aperture or ISO, or some combination of these. There is nothing separate called 'exposure'.

As you said on you first post it is all about Shutter, Speed, Aperture and ISO.

When I process my photos there is a slider for exposure. This may be the question.

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Originally Posted by MrB

Exposure is the input to the camera's sensor when taking the photograph - the amount of light that reaches the sensor, which depends upon the luminance of the scene, the size of the lens aperture, and the exposure time (i.e. shutter speed). The ISO value is an amplification factor applied to the output from the sensor, to brighten the resultant image to a level acceptable to the viewer - this can be applied in-camera or in post-processing.

Cheers.
Philip

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Exposure is including the isso setting. Exposure means the desired settings to come to a certain image. The isso setting, and the thereby belonging values for A and S are one.
Or we have two different exposure definition: an analogue and a digital to make it more difficult.

George

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Originally Posted by Dave Humphries

I do not disagree with any of the above replies, but (to be pedantic/thorough) there is a fourth variable - the amount of light, which it may be possible to increase; e.g.
a) if shooting still life indoors by window light, open the curtains/drapes/blinds more, or take down the net curtains - this latter is probably a UK phenomena only :)
b) if shooting by flash (or continuous artificial light), increase the power and/or move it closer to the subject

Of course, if the exposure problem was caused by the subject being too bright, reverse all the logic of my suggestions.

Cheers, Dave

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Brilliant!

In these days of auto-everything, the original meaning of "exposure" appears to be fading away ;)

Since exposure is really how much light falls on the sensor (lux) times how long for (sec) we only have two direct controls on the camera and neither of them is the ISO knob :D.

The other direct control, just as Dave says, is the lighting.

Therefore the so-called Exposure Triangle should be Lighting, Aperture, Shutter.

And for the pin-hole lens, we just have the Exposure Line ;)

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Originally Posted by bertam

He then adjusted a dial (which I thought was an exposure adjustment) which enabled him to lighten or darken the image to his requirements. Is this not exposure?

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Many cameras have a dial commonly called an "exposure compensation" dial and that's probably the dial you saw being used in the tutorial. Depending on the camera's exposure mode being used at the time and other factors that would be too confusing to explain, that dial will alter the exposure by automatically adjusting either the shutter speed or aperture and possibly also the ISO value.

It's called exposure compensation because using the dial compensates for the exposure that was automatically determined by the camera. When the camera determines an exposure that is not to your liking, you can compensate by using that dial to produce a generally brighter or darker exposure.

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Originally Posted by xpatUSA

Since exposure is really how much light falls on the sensor (lux) times how long for (sec) we only have two direct controls on the camera and neither of them is the ISO knob.

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I don't have a technical background, but my understanding is that the basic concept of exposure has not changed since the earliest days of photography. There have always been three aspects: the sensitivity of the material the light is falling upon (whether it's metal, glass, paper, film or an electronic sensor), the amount of time the light is falling on that material and the amount of light being allowed to fall upon that material.

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Originally Posted by bertam

I saw a tutorial where the tutor set the 'three elements' then he looked at the screen and said it was too dark. He then adjusted a dial (which I thought was an exposure adjustment) which enabled him to lighten or darken the image to his requirements. Is this not exposure?

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Ahhh, that control is the Exposure Value (EV). It provides you a way to control the combination of factors that make up exposure based on the settings on your camera.

If you are in something other than manual control mode the EV control will cause a change to the aperture, shutter speed and/or the ISO depending on capabilities and other settings on your camera.

For example you might have auto-ISO set and that tells the camera that it is free to change the ISO as necessary. If that is the case then +1 EV will double the ISO. It can get pretty complex, basically you are allowing the computer in the camera to take control of the factors controlling exposure.

If you are in Aperture mode, the camera may change shutter speed or ISO to give a particular exposure.
If you are in Shutter Priority mode, the camera may change aperture or ISO to give you the identical exposure.

This control has limits however. You can't exceed the maximum or minimum aperture of a lens for example. You may have menu options to make for a maximum ISO or minimum shutter speed and the camera, of course has it's own limits like the lens.

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Originally Posted by Mike Buckley

I don't have a technical background, but my understanding is that the basic concept of exposure has not changed since the earliest days of photography. There have always been three aspects: the sensitivity of the material the light is falling upon (whether it's metal, glass, paper, film or an electronic sensor), the amount of time the light is falling on that material and the amount of light being allowed to fall upon that material.

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Can't agree, Mike, sorry.

Exposure has long been defined as, e.g., "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."

https://en.wikipedia.org/wiki/Exposu...photography%29

Please note that the sensitivity of the material is not mentioned as an aspect.

Getting silly: if I were to replace the sensor or film by a piece of toilet paper the exposure would not be changed a whit.

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Originally Posted by xpatUSA

Exposure has long been defined as, e.g., "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."

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This is a classic example of a scientific definition that contradicts other widely recognized definitions and explanations of the concept. It may be scientifically accurate but it is misleading in and of itself for those of us who don't have a scientific background.

I think Mike's take on the dial being EC (Exposure Compensation) is probably the most likely explanation of what Bertam saw.

Failing that Didace's thought on it being the view of a control in an image editor is another possibility.


Please let's all cease the off-topic/unhelpful discussions of word definitions.


Bertam, it would be useful if you could provide a link to the video you were watching, if possible, or tell us where you saw it, at least - a little more context would help us.

Thanks, Dave

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Originally Posted by Dave Humphries

Please let's all cease the off-topic/unhelpful discussions of word definitions.

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Amen to that!

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Originally Posted by Dave Humphries

Please let's all cease the off-topic/unhelpful discussions of word definitions.

Thanks, Dave

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I will comply with the intent, Dave, while finding it difficult to understand that a correct definition of "Exposure" is off-topic/unhelpful in a thread titled "Exposure"!

In the manner of Galileo, I recant. Putting 400 ASA film in, instead of 100 ASA, does affect the exposure . . ;)

Thanks Ted,

I guess it was me that started us all off down that line too :(


It is about getting back to the context of the initial plus follow up query (it being a 'dial' on something) that makes the definition discussion unhelpful to Bertam.

This is one of those threads in which I wish people would look at what a relatively new member has asked. If people want to take the discussion off into another related area to avoid the possibility of totally confusing and intimidating a new member who's trying to learn the basics, then that would be more helpful.

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Originally Posted by Dave Humphries

Please let's all cease the off-topic/unhelpful discussions of word definitions.
Thanks, Dave

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Much confusion arises (in many areas of life) because words that have perfectly good and simple definitions are used incorrectly, and some people cannot be bothered to change their bad habits.

The definition of exposure is stated clearly and simply in Post #4, as is the effect of the ISO value. If people were to stick to correct definitions, and use the terms correctly and without any need to get technical, others might find it much easier to gain a useful and deeper understanding of the basics.

And even a CiC tutorial writing about the "exposure triangle" doesn't make it right - it is not an exposure triangle, it is an image brightness triangle.

Cheers.
Philip

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Originally Posted by Saorsa

Ahhh, that control is the Exposure Value (EV). It provides you a way to control the combination of factors that make up exposure based on the settings on your camera.

If you are in something other than manual control mode the EV control will cause a change to the aperture, shutter speed and/or the ISO depending on capabilities and other settings on your camera.

For example you might have auto-ISO set and that tells the camera that it is free to change the ISO as necessary. If that is the case then +1 EV will double the ISO. It can get pretty complex, basically you are allowing the computer in the camera to take control of the factors controlling exposure.

If you are in Aperture mode, the camera may change shutter speed or ISO to give a particular exposure.
If you are in Shutter Priority mode, the camera may change aperture or ISO to give you the identical exposure.

This control has limits however. You can't exceed the maximum or minimum aperture of a lens for example. You may have menu options to make for a maximum ISO or minimum shutter speed and the camera, of course has it's own limits like the lens.

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I looked on all my cameras and could not find an Exposure Value (EV) control or function anywhere but the use of caps does imply that such a label exists. While most of us probably realize what is meant by "Exposure Value (EV) control", I'm not convinced that inventing a new term for Exposure Compensation will help Bertam that much.

Perhaps I'm wrong . . does a Canikon have a so-named control? Fuji? Sony?

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Originally Posted by MrB

Much confusion arises (in many areas of life) because words that have perfectly good and simple definitions are used incorrectly, and some people cannot be bothered to change their bad habits.

The definition of exposure is stated clearly and simply in Post #4, as is the effect of the ISO value. If people were to stick to correct definitions, and use the terms correctly and without any need to get technical, others might find it much easier to gain a useful and deeper understanding of the basics.

And even a CiC tutorial writing about the "exposure triangle" doesn't make it right - it is not an exposure triangle, it is an image brightness triangle.

Cheers.
Philip

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You must distinguish between a measured quantity and a wanted quantity. You're talking about a measured quantity. In photography a wanted quantity is ment, based on the sensitivity of the film or the sensor/amplification. So the exposure trangle is right.

I don't think you can change the iso-setting in pp.

George

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Originally Posted by xpatUSA

I looked on all my cameras and could not find an Exposure Value (EV) control or function anywhere but the use of caps does imply that such a label exists. While most of us probably realize what is meant by "Exposure Value (EV) control", I'm not convinced that inventing a new term for Exposure Compensation will help Bertram that much.

Perhaps I'm wrong . . does a Canikon have a so-named control? Fuji? Sony?

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Yes, This is the top of Nikon D90
http://www.cameralabs.com/reviews/Ni...t_controls.jpg

the +/- to the right of the on of switch with a green dot next to it is the EV control.

Canon calls theirs Av adjustment and use the same symbol

http://www.wexphotographic.com/blog/.../2013/07/Q.jpg

and here it is on the Merrill at top right most convenient for the index finger.

http://1.static.img-dpreview.com/fil.../Topright.jpeg

I see something similar on the Sigma as Av with a plus and minus

http://www.letsgodigital.org/images/...sigma_sd15.jpg

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Originally Posted by Saorsa

Yes, This is the top of Nikon D90
http://www.cameralabs.com/reviews/Ni...t_controls.jpg

the +/- to the right of the on of switch with a green dot next to it is the EV control.

Canon calls theirs Av adjustment and use the same symbol

http://www.wexphotographic.com/blog/.../2013/07/Q.jpg

and here it is on the Merrill at top right most convenient for the index finger.

http://1.static.img-dpreview.com/fil.../Topright.jpeg

I see something similar on the Sigma as Av with a plus and minus

http://www.letsgodigital.org/images/...sigma_sd15.jpg

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Brian, we need to discontinue this. None of these buttons are called "Exposure Value".

For example DP Review says:

http://1.static.img-dpreview.com/fil...pcontrols.jpeg

"Behind this are four buttons; metering mode, exposure compensation, drive mode and AF mode."

And my Sigma SD1M manual says:

" . . press the exposure compensation button . ."

If you want to confuse Bertam by calling these buttons something else, I can't stop you so I'll just shut up . . .

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Originally Posted by george013

You must distinguish between a measured quantity and a wanted quantity. You're talking about a measured quantity. In photography a wanted quantity is ment, based on the sensitivity of the film or the sensor/amplification. So the exposure trangle is right.

I don't think you can change the iso-setting in pp.

George

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The facts in Post #4 are plain, simple, and correct.

Trying to keep it simple, some simple examples, requiring no measurements, just simple observation of the information in the viewfinder or screen:

Exposure:

E.g. 1. I want to use f/11 for more depth of field for this scene; that small aperture will not allow enough light to the sensor for the camera to give a sufficiently bright image, but I can balance that by slowing the shutter speed down to 1/60s, opening the shutter for longer to allow more light to reach the sensor.

E.g. 2. I want to use a shutter speed of 1/500s to freeze the movement of this subject; that will not allow enough light to the sensor for the camera to give a sufficiently bright image, but I can balance that by opening up to f/4, a wider aperture allowing more light to reach the sensor.

Brightening:

E.g. 1. I want to use a shutter speed no slower than 1/100s with this lens, in an attempt to avoid image softening by camera shake. I also want to use f/8 to give a reasonable depth of field. However, these exposure settings will give an image that will be too dark. But I can increase the camera's ISO setting, so that the camera will brighten the image that it produces.

E.g. 2. I want to use a shutter speed no slower than 1/100s with this lens, in an attempt to avoid image softening by camera shake. I also want to use f/8 to give a reasonable depth of field. However, these exposure settings will give an image that will be too dark. But I can use my post processing software to brighten the dark image that the camera produces.

Cheers.
Philip

OK, I think the OP's question has been answered, so I am going to allow myself to respond to the back-and-forth about terminology.

I think Philip is exactly right. That's why, for example, EV (exposure value) is defined without reference to ISO. And while most of us will slip into a colloquial use of terms like "exposure triangle" without any harm being done, I think it is helpful to keep the concepts straight.

I'll give another example to extend Philip's. Suppose I take an underexposed image. Let's say its BADLY underexposed, say, by 4 stops. I then open the image in software and try to correct for this underexposure. Just for the sake of illustration, let's say it's photoshop, and the tool I use to compensate for my underexposure is the levels tool. I just crank up the brightness until it has the brightness it would have had if it had been properly exposed. Would anyone then say that it was a properly exposed image? I wouldn't. It wasn't properly exposed; I just compensated in software.

Increasing ISO is technically different, but it is in principle exactly the same: it compensates for underexposure by amplifying the signal from the sensor. In fact, in the case of ISO-less sensors, you will get pretty much the same result regardless of which way you compensate.

Sometimes this won't matter in practice, but sometimes it does.

What an interesting discussion! I've learned so much, even when we went a little off topic it was still beneficial. What I'm taking away from the discussion is this; having set the three pillars and still finding the image too light or dark, an additional setting (which has different names on different cameras) called EV overrides the original settings to lighten or darken the image. Thank to everyone your input is really appreciated. Sorry I couldn't provide the link as was requested. I tend to trawl the net without taking particular notice of the location.

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Originally Posted by DanK

And while most of us will slip into a colloquial use of terms like "exposure triangle" without any harm being done

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For the record, I didn't "slip" into anything. Everything I've been taught about photography from my first days in the mid-1980s by a Kodak series of books about the basics of photography is that exposure is comprised of three values, exactly as explained in the CiC tutorial. To learn today for the first time that there is another definition is alarming. It's especially alarming to be artfully informed by Philip that "some people can't be bothered to change their bad habits." If he wants to include me in that group, that's very shamefully his problem, not mine. I didn't come to my understanding by a series of bad habits and I'm reasonably confident that there is an entire community of photographers that the same is true for them.

Not only there is no harm being done for using so-called colloquial terminology, it's actually extremely helpful to use it because such a large number of photographers if not the vast majority of photographers have been trained to use that terminology. If someone wants to use terminology that is so-called correct but understood by only 10% of the community of photographers as opposed to using terminology that is so-called incorrect but clearly understood for practical application by 90% of the community of photographers, that person in my mind is a LOT more interested in being able to stand in the camp of being so-called correct rather than in the camp of effectively communicating with photographers the practical application of the tools available to them.

Do I understand how to practically apply the tools of exposure in the real world of photography? You betcha! I knew how to do it with film photography and I know how to do it with digital photography. Do I understand the scientific definition of those tools? Apparently not. Do I care? Not in the slightest.

Pluto used to be a planet. Though Pluto didn't change, it's no longer a planet. Thank the scientists for those two "facts."

Now that we've helped Bertam to the extent that he now understands that "an additional setting (which has different names on different cameras) called EV overrides the original settings to lighten or darken the image." (my emphasis) . . .

. . . I'll continue my recant, started earlier :D

ISO is an essential part of The Triangle, which would collapse and become meaningless without it.

There is no such Standard as ISO 12232 - the very definition of the acronym "ISO" used for The Triangle.

Even if there were such a Standard, it does not contain, in Section 4.2:

" . . . where Ha is the arithmetic mean focal plane exposure, expressed in lux-seconds (lx⋅s)"

Neither does this non-existent Standard make any other references to "exposure" on page after page after page after page . . .

So I must conclude that exposure is just the brightness of an image after all . . and rebut any suggestion that my Sigma raw data is not immediately affected by "an amplifier" in-camera any time I touch the ISO knob.

And the Earth, of course, is flat.

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Pluto used to be a planet. Though Pluto didn't change, it's no longer a planet. Thank the scientists for those two "facts."

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Whether Pluto is considered a planet is a classification, not a fact. What changed is the facts available to astronomers about Pluto and its environs, which led people to suggest changing the classification. One could use a different classification. That wouldn't change the facts. An explanation can be found here.

But we digress, as Gail Collins likes to write.

I don't think there is any need for acrimony here. Mike, I didn't accuse you of anything; if anything, I put you and me in the same boat.

And I don't think only 10% of people understand this. People are just inconsistent in their terminology. I'll wager than in the example I gave--underexposing by 4 stops and brightening in software--you too would not call the image properly exposed.

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Originally Posted by DanK

I don't think there is any need for acrimony here.

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Agreed. I have no acrimony whatsoever.

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Mike, I didn't accuse you of anything

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Also completely agreed.