What is Shutter Speed?

In the simplest of terms, shutter speed is the amount of time that light hits the film. The shutter is the little curtain that opens and closes when you push the release button (when you make an exposure).

Exposure is effected by both the time and the intensity that light hits the film. In general, the correct exposure for all film is about the same amount of total light energy absorbed. Since we know that film sensitivity to light varies with ISO (formerly ASA), and that we can control the amount of light that reaches the film with shutter speed and aperture, we can use this formula to express total exposure:

Exposure = Intensity x Time (E = It)

In complicated photography/optics terms, intensity has other factors but is partially controlled by aperture settings. In laymen’s terms, this formula basically means that if you increase the aperture, you need to decrease the shutter speed (or film speed)… or that if you increase shutter speed you need to reduce aperture… or any mix n’ match of the three. Hence the exposure triangle of aperture, shutter speed, and ISO:


Each element effects the others and must be adjusted accordingly… but more on that in “Exposure.” For now, let’s get back to shutter speed:

On most cameras, shutter speeds increase by a ratio of 1:2 (w/ several rounded values), for example:

1/2  1/4  1/8  1/15 1/30 1/60 1/125 1/250 1/500 1/1000 1/2000 1/4000

1/60 is one sixtieth of a second. 1/1000 is one one thousandth of a second.

Most shutters also have a B and or T function; “B” stands for “bulb” and leaves the shutter open as long as you press it. “T” stands for “Time” and you press the shutter once to open, and again to close. “T” obviously makes more sense if you needed to do an exposure that was minutes or more. (If like myself, your camera doesn’t have a “T” function, you can always lock a cable release for extended exposures)

1/60 is the lowest you can go without a tripod before you will have camera shake; and even at 1/60 you need to be standing still.

For flash sync: the majority of cameras made before the 90’s sync with an external flash at 1/250; newer cameras can also have a flash synch at 1/200. (If you’re not sure what shutter speed your camera syncs at, be sure to look it up because using the wrong sync speed will mean half of your photograph is exposed, and the other half is black.)

Types of shutters:

Leaf Shutter- a leaf shutter has overlapping blades that are controlled by a rotating ring. It looks not unlike a star:


A leaf shutter is located at the base of the lens, near the diaphragm. For those of you who are familiar with focal plane shutters, opening up the back of a camera with a leaf shutter will look like a focal plane shutter that is stuck on open.

(Note: view cameras are almost exclusively leaf shutters (unless there’s a super fancy new view camera I haven’t heard about, which is totally possible) and feature a manual setting to open the shutter for viewing)


Focal Plane Shutter - a focal plane shutter is mounted near the film plane and features a horizontal curtain. Actually, older focal plane shutters feature one curtain, most new focal plane shutters now have two curtains:


To help understand the main difference between leaf and focal plane shutters, I am going to quote Ansel Adams, who again explains it much better than I ever could:

“An important difference between focal plane shutters and leaf shutters, is that the latter always expose the entire film area at the same time, while the focal plane shutter, when set at faster speeds, exposes a continuously overlapping series of strips.”  {Ansel Adams, The Camera, p. 85}

Both have their drawbacks, and for the focal plane shutter this mainly has to do with fast moving subjects and image compression. Basically, when you’re subject is moving really, really fast (for example, a car) it will probably be in a different place at the end of the exposure than it was at the beginning, which results in the image being either stretched or compressed. Depending on whether your focal plane shutter is horizontal or vertical, this stretching or compressing with take place either (you guessed it) horizontally or vertically. Because a leaf shutter exposes the entire film area at once this distortion will not occur, however - yes there is a however because leaf shutters are not without flaw - also because a leaf shutter exposes the entire film area at once (versus the small slits of the focal plane) very high shutter speeds are not possible. There are not very many leaf shutters manufactured today.
Please be sure to head over to The Photon Fantastic for A Beginner’s Guide to Lenses