A range of shutter speeds is available on professional cameras. Common shutter settings are as follows: T, B, 1 second, 1/2, 1/4, 1/8, 1/15, 1/30, 1/60, 1/125, 1/250, 1/500, 1/1000, and 1/2000 second. The fastest between-the-lens (leaf) shutter speed is 1/500 second. Some focal-plane shutters can be as fast as 1/12000 second. In addition to a given set range of speeds, most shutters are made so they can be opened for an indefinite period of time. At the setting marked "T" (time), the shutter opens the first time the shutter release button is depressed and remains open until the shutter release button is depressed again. At the setting marked B (bulb), the shutter remains open as long as the shutter release button is depressed, but closes as soon as it is released.

The interval that you want the shutter to remain open is selected by moving a lever or shutter speed dial to that particular setting on the shutter speed scale. Unlike f/stops, the shutter speed you select must align exactly with the index mark You cannot select a shutter speed in between two indicated shutter speeds. On the shutter speed dial, the top part of the fraction (numerator) is not indicated; for example, the shutter speeds 1/60, 1/125, 1/250, and so forth, are indicated as 60, 125, and 250.

When a camera with a focal-plane shutter is used with an electronic flash, a predetermined shutter speed must be set. At this speed the shutter and flash unit are said to be in synchronization. When the flash and shutter are synchronized, the shutter opening is wide open at the same instant the flash fires. Usually, the slowest shutter speed that syncs with a flash unit is indicated in red or another off color or a lightning bolt symbol on the shutter speed dial.

Function

The shutter serves two functions: controlling the duration of the exposure and controlling subject movement. These two functions are entirely separate and distinct. You must determine the shutter speed required for each condition. After determining the shutter speed, you select the f/stop that provides the correct exposure for the film speed and lighting conditions. Normally, the duration of exposure is short enough to prevent image blurring. You can always set the shutter speed faster than the speed required to stop image motion, but it should not be longer if you want the image to be sharp; for example, when a shutter speed of 1/125 is sufficient to stop subject motion, you can set the shutter speed to 1/250 or faster, but not at 1/60 if you want to stop the motion and produce a sharp image. Each time you change the shutter speed, the diaphragm is adjusted to produce a properly exposed image.

The correct sequence in determining the diaphragm and shutter to produce a properly exposed negative is as follows:

1. Compose and focus the image.

2. Stop down or open up the diaphragm until the desired depth of field is achieved.

3. Select the shutter speed that will produce a proper exposure when combined with your aperture setting.

4. Determine whether the shutter speed is fast enough to prevent image blurring.

5. If the selected shutter speed is too slow, reset it to a faster speed and open up the aperture accordingly.

When you increase the shutter speed, you compromise and loose depth of field. Sometimes this is the only way to produce a useable image. If you cannot sacrifice some depth of field, there are several alternative you can use: select a faster film, increase the camera-to-subject distance, select a shorter focal length lens, or change the camera angle, so the relative motion of the subject to the camera is decreased.