Focal plane shutter
A mechanism for the shutter that is located directly in front of the image sensor, in the focal plane of the lens. It is made up of two curtains that block out all of the light and move across the focus plane with a little gap in between them when the shutter speed is set to a fast value. In order to expose the image sensor or film, light has to go through this slit. When using shutter speeds that are slower than the flash sync speed, one curtain will cross the focal plane to expose the entire sensor or frame of film, and then the second curtain will traverse the focal plane separately after the first curtain. This sort of shutter is frequently seen on digital single-lens reflex cameras.
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