Exposure is not how dark or how light an image looks!

Technically, exposure is a combination of sensor illuminance and shutter speed. Sensor illuminance can be calculated from scene luminance (anybody remember the light meters that read out in luminance?) and f/stop.

It is common for photographers to omit scene luminance when talking about exposure.

Q: "What exposure did you use for that shot?"

A: "I gave it 1/125 at f/8."

I think it's too late in the game to insist on always referencing scene luminance when talking about exposure, but when the discussion is technical, I think the role of scene luminance should not be forgotten.

Thank you for the elaboration. At least we can teach to remove the mention of ISO from the answer to "What exposure did you use for that shot?".

In your opinion, is there an unambiguous definition of over/under-exposure?

To me, they mean exposures that are greater or less than the exposures that, after reflection and with great wisdom, the photographer would choose were there the opportunity to repeat the captures.

It is because of that inappropriate disconnection that we have many people saying over/under exposed when in reality they mean too light or too dark.

For the sake of clarity and consistency, especially in a Beginners Forum the meaning of the word exposure should be the same as when it is used by itself or when saying over/under exposed.

Having different meanings for words depending on the context can lead to only confusion and misconceptions in a Beginners Forum.

* exposure - amount of light striking the sensor per unit area while the shutter is open
** optimal exposure - the maximum exposure* within dof and motion blur requirements without clipping important highlights.
*** under exposed - more exposure* could have been added with the DOF and blur constraints still being met without clipping important highlights.

Why do you think that the meaning changes?

so you have just walked into the studio to shoot a product/model and you set exposure of f8 1/125 sec and nothing else ! yeh right.

The single word exposure gets tied to a variety of different intended meanings. Distinguishing between exposure and Exposure Value (EV) is a good step toward better clarity in terminology. A few more suggested distinctions, which may offer some additional descriptive clarity, are between the terms exposure, exposure level, and exposure control. There are a variety of light sensitive imaging systems which may utilized, each containing a recording medium for capturing images.

In photographic terms, Exposure is an event which produces a quantity of light onto a light sensitive surface over a period of time. Exposure Level is the effect that an exposure event has on a light sensitive medium which can be measured and recorded. Exposure Control is the balancing of the input level of light with the sensitivity level of the recording medium to achieve the desired tonality and other qualities of an image. Accurate exposure control is necessary to record the range of desired brightness levels in a scene and balance tonality effectively in the image you envision and intend to produce.

Despite our best efforts at exposure control, or those of a camera's auto exposure system, we may have an imbalance among the variables which results in a poorly recorded image. The exposure value chosen may produce scene brightness levels which are higher or lower than you desire for the recording medium. This may result in the range of recorded brightness levels being too high or low to be considered either optimal or within your tolerance for deviation from your quality standards. In the photography world, these poor quality results are referred to as overexposure and underexposure. There are a variety of potential remedial actions within the imaging chain which may improve the result, but those are separate from the terms which have long been applied in describing images which exhibit undesirable brightness and tonality characteristics in their recorded representation of a scene.

The reason has been explained on more than one occasion already by Michael Fryd, myself and maybe others earlier in this thread. No need for me to repeat again.

* exposure - amount of light striking the sensor per unit area while the shutter is open
** optimal exposure - the maximum exposure* within dof and motion blur requirements without clipping important highlights.
*** under exposed - more exposure* could have been added with the DOF and blur constraints still being met without clipping important highlights.

Under- and over-exposure are terms by themselves; they do not contradict or change the meaning of exposure. As Jim and a few other mentioned, they mean being below or above the intended exposure.

It depends on the meaning of exposure someone uses. Many regard exposure as just how light or dark an image looks and so they see over/under exposure as meaning if in their opinion the image looks too light or too dark regardless of the exposure* that was set.

I could have set the optimal exposure** but the image could still be too dark if the ISO was set too low. In this case the image is not under exposed*** because I could not have added more exposure* without messing up my DOF or blur requirements. The image is just simply too dark.

In any case, for the sake of clarity I include the definitions of 'exposure', 'optimal exposure' and 'under exposed' in my signature so everyone can at least see what I mean when I use the terms in posts.

* exposure - amount of light striking the sensor per unit area while the shutter is open
** optimal exposure - the maximum exposure* within dof and motion blur requirements without clipping important highlights.
*** under exposed - more exposure* could have been added with the DOF and blur constraints still being met without clipping important highlights.

And not just in how the print looks but in how the image looks on someone else's screen as well.

I sense that many people incorrectly assume that how an image looks on there screen is exactly how it looks on the image creator's screen which in many cases could be significantly different.

For example, if someone has their screen brightness set way higher than mine is then obviously my images, although looking perfect on my screen will most probably be too light on the screen of the person viewing my image. It is technically incorrect for that person to say my image is over exposed unless they were certain I used a greater than optimal exposure**.

All the other person can say with accuracy is that my image looks too light on their screen for their taste.

I don't understand the point you're trying to make.

thank you , the article constantly references "recording medium" with digital we have a "variable recording medium" which now needs to be set as the 3rd adjustment for exposure to be classified as correct exposure/image brightness for a given scene representing the photographers intent and purpose of the image. ;-) that was a mouth full :-)

Your quote " It is common for photographers to omit scene luminance when talking about exposure.

Q: "What exposure did you use for that shot?"

A: "I gave it 1/125 at f/8."

its not common for any photographer to omit iso or lighting given ambient or artificial. no one ever talks just exposure, because it has no meaning by itself.

It's not an article, just a forum post. For more depth, I've previously linked an excellent and informative article; but that's still just a beginning.

You'll find "recording medium" three times, once in each paragraph. You need a medium to record the light values — or the exercise is all in vain. Either film or an electronic image sensor will work for this discussion.

We have variable ISO ratings and settings for film and image sensors...

...which have always been part of the calculation to determine exposure value.

That's always been the end goal.

Photographers may include or omit many things depending on the current topic of discussion and context.

Sure it does. "1/125 at f/8" represents an exposure value of EV 13. That's the approximate exposure value for ISO 100 on a cloudy day.