What's the difference between exposure and shutter speed?

Question

Is there a difference between exposure and shutter speed, or are the terms interchangeable? I read that "If you use a quick shutter speed, you can just raise the exposure to compensate." Is this statement invalid, or is there a difference?

Answer 1

The term "exposure" is used for a number of different but related things in photography. I can see how this might be confusing. Here are five different ways in which it is used:

1. The combination of all factors which make a photograph have a certain overall brightness. The key factors are shutter speed, lens aperture, and sensor or film sensitivity (a.k.a. ISO), in combination with the light levels in the scene itself. Sometimes, post-processing can also be involved, as in "pushing the exposure" when developing film or with an "exposure" slider in a RAW development program.
2. The amount of light allowed to to fall on an area of the sensor or film. This is related to the previous sense, but is more strict. It's arguably more technically-correct, but I think the wider definition is more common these days. Here, though, ISO sensitivity (and definitely post processing) aren't included — it's the light in the scene combined with the size of aperture you use combined with the time the shutter is open. In this sense, one might say that the same exposure yields different results at different ISOs.
3. Exposure time — A synonym for shutter speed. Or, technically, exposure time is the result of a certain shutter speed. Sometimes one might hear just "exposure" for this, but usually this sense is qualified with the word "time", or in combination with some unit of time (as in: "Exposure: 30 seconds"). "Shutter speed" is itself jargon, since we don't really mean the speed at which the shutter travels.
4. The result of a single click of the shutter. An HDR image, for example, may be said to be composed of multiple exposures — several images taken in a row.
5. Occasionally, a term for a photograph, usually used in a semi-technical or jargon-ish way. (Probably referring to unsorted, unedited negatives or proof prints, or a collection of images just dumped off a memory card.)

Exposure value is a common technical term which uses the first sense in the list above. You can read more about that in the question What is the EV scale?.

Confusion between sense #1 and sense #2 above sometimes results in long, pedantic flamewars between people who both think the other person is wrong, and don't realize that they're actually talking past each other.

In the example sentence you give, "If you use a quick shutter speed, you can just raise the exposure to compensate", I think the term is simply accidentally misused and that they probably meant "ISO sensitivity". Raising the exposure (or exposure value) doesn't really make any sense in that context.

Answer 2

Exposure is a combination of three things:

Aperture - the size of the opening in the lens through which light passes

Shutter Speed - the time which the sensor is exposed to the light

ISO sensitivity - the sensitivity of the sensor to the light it is exposed to.

So there isn't really a difference between shutter speed and exposure, but it's part of what makes an exposure.

In the text you read, when using a faster shutter speed, the sensor won't have so much time to "see" the scene, so you might consider using a larger aperture (a smaller f stop), or increasing the ISO sensitivity of the sensor, to compensate.

Answer 3

I am still researching this topic, because in no place i can find information about shutter speed. Speed is a function of distance vs time, while the shutter controls only time. We don't know the actual speed pf the shutter mechanism, nor we have to care about it. So i think the technical figure is "time of exposure" and that shutter speed is an arbitrarily one.

Answer 4

Photography is all about exposure, both in experience and light captured. When you heard:

If you use a quick shutter speed, you can just raise the exposure to compensate.

They may have been referring to Exposure Value.

As stated before, you can change the exposure in a few different ways. Most basically Aperture and Shutter speed. Assuming you know what both are, you can shoot in aperture priority or shutter priority. Or fully manual where you control both. You also can change the EV (Exposure Value).

If you can manually change the aperture and shutter speed to control exposure, why bother having EV?

Well, in aperture priority, changing the EV actually changes the shutter speed (or ISO) accordingly. You might want a particular Depth of Field.

In shutter priority, the EV value will change the aperture (or ISO) accordingly. Again here, you might want a blur effect where the DoF doesn't really matter.

And again, ISO changes the sensitivity of the sensor. In the film days, a roll of film was graded with an ISO value. Most commonly 100, 200 or 400. So it's great in this digital world you can just press a button!

A low ISO value means it's not very sensitive to light so you can have a brighter exposure. A high ISO value means it's more sensitive to light, so you can have darker exposure. But, the higher the ISO, the more grainy the results.

Answer 5

Briefly, exposure is a combination of factors all of which together tell you how much light accumulates on the sensor to make the picture. Shutter speed is only one aspect of exposure. The three major factors are ISO (sensor or film sensitivity), f-stop (how much light the lens lets thru), and shutter speed (how long the light has to accumulate on the sensor of film).