The aperture is modulated via a shutter. An active shutter 3D system uses electronic shutters. Many mirrorless cameras retain a mechanical shutter. Early cameras have a 190 degrees opening angle shutter. These cameras employ photodetectors with a fast electronic shutter. The original system involved shooting with three synchronized cameras sharing a single shutter. The cameras were unique in using a rotary shutter. Leaf shutter lenses had a separate PC socket. The SLR670a allows for additional shutter/brightness control. Smartburst is activated by holding the shutter button down. Early CCD sensors suffered from shutter lag. The following list provides an overview of common photographic uses for standard shutter speeds. Lacking a physical shutter, some have a long shutter lag. Earlier models had a separate mechanism for cocking the shutter. A roller shutter or sectional overhead door is one variant of this type.