instead of the m42 screw mount used by pentax and other camera manufacturers, nikon had introduced the three-claw f-mount bayonet lens mount system, which is still current in a modified form today. the focal plane shutter, unlike other slrs of the period which used a cloth material for the focal plane shutter design (note: with this design, it was possible to burn a hole into the cloth of the shutter during mirror lock-up in bright sunlight) used titanium foil which was rated for 100,000 cycles of releases of the shutter (according to nikon). the f was also a modular camera, in which various assemblies such as the pentaprisms, the focusing screens, the special 35mm roll film 250 exposure film back and the speed magny film backs (two models: one using the polaroid 100 (now 600) type pack films; and another speed magny was designed for 4×5 film accessories, including polaroid's own 4×5 instant film back). these could be fitted and removed, allowing the camera to adapt to almost any particular task. it was the first 35 mm camera offered with a successful motor drive system.