Focal-plane shutters

Almost all contemporary SLRs use a focal-plane shutter located in front of the film plane, which prevents the light from reaching the film even if the lens is removed, except when the shutter is actually released during the exposure. There are various designs for focal plane shutters. Early focal-plane shutters designed from the 1930s onwards usually consisted of two curtains that travelled horizontally across the film gate: an opening shutter curtain followed by a closing shutter curtain. During fast shutter speeds, the focal-plane shutter would form a 'slit' whereby the second shutter curtain was closely following the first opening shutter curtain to produce a narrow, vertical opening, with the shutter slit moving horizontally. The slit would get narrower as shutter speeds were increased. Initially these shutters were made from a cloth material (which was in later years often rubberised), but some manufacturers used other materials instead. Nippon Kōgaku (now Nikon Corporation), for example, used titanium foil shutters for several of their flagship SLR cameras, including the Nikon F, F2, and F3. Nowadays these shutters are very rarely found in new SLRs, though Leica continues to use them in their M-System rangefinders.
Other focal-plane shutter designs, such as the Copal Square, travelled vertically - the shorter travelling distance of 24 millimetres (as opposed to 36 mm horizontally) meant that minimum exposure and flash synchronisation times could be reduced. These shutters are usually manufactured from metal, and use the same moving-slit principle as horizontally travelling shutters. They differ, though, in usually being formed of several slats or blades, rather than single curtains as with horizontal designs, as there is rarely enough room above and below the frame for a one-piece shutter. Vertical shutters became very common in the 1980s (though Konica, Mamiya, and Copal first pioneered their use in the 1950s and 1960s, and are almost exclusively used for new cameras. Nikon used Copal-made vertical plane shutters in their Nikomat/Nikkormat -range, enabling x-sync speeds from 1/30 to 1/125 while the only choice for focal plane shutters at that time was 1/60. Later, Nikon again pioneered the use of titanium for vertical shutters, using a special honeycomb pattern on the blades to reduce their weight and achieve world-record speeds in 1982 of 1/4000 second for non-sync shooting, and 1/250 with x-sync. Nowadays most such shutters are manufactured from cheaper aluminium (though some high-end cameras use materials such as carbon-fibre and Kevlar).