Digital Camera Shutter

The shutter has some variable characteristics depending on the kind of camera. First of all, there are two types of shutters, each radically different in design and operation: the central shutter, installed inside the lens next to the diaphragm, and the focal plane or curtain shutter, places in the body of the camera next to the film. The camera manufacturers choose on or the other according to the camera they are designing.

The Central Shutter
Is historically the first kind of mechanical shutter. It blocks the light when passing through the lens and it's mobile parts are thin metal plates, similar to the diaphragm, situated transversally and concentric, in regard to the axis of the lens (the line which unites the centers of all it's lenses). Therefore, when it is close we can't see the image projected by the lens.

This is the shutter used on almost all direct viewfinder and TLR cameras, and is opened only during exposure; that of a large format camera, were we frame with the shutter open and close it to introduce the film; and, even though it may seem incompatible, it is also used in medium format reflex cameras (SLR). In this case, when the shutter is open to frame, the film is protected by an auxiliary shutter.

When shooting with a central shutter, every blade quickly moves away from the lens' axis until completely letting the light through; it stays in this position during the exposure selected, after which it goes back to it's original position.

Observe that at any speed, the shutter stays completely open at least for an instant, when the blades are finishing opening, they stop and invert there movement. The main advantage of this type of shutter is that it's very precise, small and causes almost no vibration independently from the format of the camera. If flash is used it can be synchronized with any shutter speed (9.4).

The biggest disadvantage associated with the central shutter is that it is placed inside the lens, which makes interchangeable lenses very expensive.