Exposure?

[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'?

[Shadowman]

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

[Saorsa]

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'?

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.

[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

[DickyOZ]

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

[DanK]

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

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.

[Donald]

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'?

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'.

[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

[Shadowman]

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

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.

[Donald]

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

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.

[Mike Buckley]

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.

[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?

[James G]

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.

[Manfred M]

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.

[Donald]

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?

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.

[Didace]

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

[george013]

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

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

[xpatUSA]

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

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 .

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

[Mike Buckley]

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?

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.

[Mike Buckley]

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.

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.