The Nikon F is one of Nikon's system-oriented SLR camera with interchangeable viewfinders, focusing screens and a comprehensive motor drive capability. The Nikon F with the Photomic prism finder was offered in 1962. The Photomic was the main distinguishing feature of the lens with its dime-sized window on the prism's front where incoming light is gathered onto a CdS photoresistor. The Photomic reads the entire view as seen by the lens and based on the average level of light, makes an exposure reading. Its film speed ranges from ASA 20 to 6400 and shutter speed of 2 to 1/1000th second, plus Bulb. The Nikon F series, the most rugged and reliable cameras made and noted as the camera that changed the direction of modern photography.