The shutter controls the length of time (speed) during which light goes through the lens to reach the film or sensor. When we take a picture, the shutter opens to allow light is through the lens to the sensor or film of a camera. The shutter is the physical element which controls the speed of exposure. In early cameras, lenses didn't have shutters and exposures were performed manually. In other words, a photograph was exposed removing the lid from the lens and controlling exposure time with a hand watch. This system was replaced with a mechanical shutter which only had a “bulb’’ and sometimes an “instantaneous”, which was used for exposures at around 1/25th of a second. These shutters were replaced with the ones we use today.
As we mentioned in the previous course, shutter speed is one of the 3 variables that control the exposure in a photograph (next to film speed and the diaphragm). Remember that the exposure is the quantity of light that a photograph needs for a desirable result (not to bright, not too dark).
The fundamental properties a shutter must posses are:
a- It needs to be as accurate as possible. This means that if I set the shutter to open for 1 second, it will really open for 1 second. Moreover, it keeps doing it every time I set it to 1 second.
b- It needs to be as silent as possible, noiseless.
c- It needs to be as steady as possible to avoid any extra Undesired) movement in the camera which might render moved or blurry photographs.
Types of shutters
There are 2 types of which are used depending on the camera format and/or model.
1. central shutter: it has a similar shape to a diaphragm. It is made of a series of metal sheets which are superimposed to prevent light from going in when closing. The shutter is located in the lens, near the diaphragm. It synchronizes with the flash at any speed; generally the maximum speed is 1/500th of a second, since the exposure happens at the same time. These shutters are used in large format cameras and many mid format cameras.
2. focal plane shutter: it is located in the body of the camera, near the film or sensor plane. It is made of 2 curtains which can move sideways or from top to bottom. The first curtain opens while the second curtain closes. If we are using high speeds, the second curtain begins to close before the first curtain has finished opening, thus, the exposure happens in parts. The maximum speed of flash synchronization (X-sync) will depend on the camera model. For example, we can synchronize at 1/60, 1/125, or 1/250th of a second. Generally, it is represented with a number in red or the sign of a lightning. Every 35mm cameras, either compact, SRL or DSRL, use focal plane shutters.