removable (interchangeable with four other viewfinders); The focusing screen can be changed out with 4 (later 9) types; the mirror can be locked up to allow deep seated lenses or for high magnification work, the back is interchangeable with a data and bulk film back (250 exposures), The bottom plate is removable and there are 4 Motor Drives and / or Power Winders that can be used (one was a special order 9 frames per second high speed motor drive); three different flash couplers allowed a wide variety of flashes; the eyepiece can take threaded diopter adjustment lenses, magnifiers or angle finders; and the lens collection numbers over 50 FD (and a few special purpose) lenses from 7.5 mm fisheye to 1200 mm super telephoto, and includes the world's fastest 300 mm at the time (the 300 mm F2.8L) and the world's fastest 400 mm lens (the New FD 400 mm F2.8L) both of which incorporate special fluorite and ultra low dispersion glass elements for superb optical quality at the widest lens opening. Viewfinders Like most professional 35 mm cameras of the 1970s, the F-1 had interchangeable viewfinders. To remove the viewfinder, one depressed the two small buttons at the rear sides of the finder, and slid the finder toward the back of the camera (or depress one button on the bottom of the Speed Finder). The camera shipped with a standard pentaprism finder, called an "eye-level finder" by Canon. Other finders available included a waist-level finder, Speed Finder, Booster T finder, and Servo EE finder. The waist-level finder was patterned after the design of waist-level finders common on medium format cameras. It had a pop-up hood to shield the focusing screen from stray light, as well as a magnifier to help with critical focusing. The waist-level finder did not allow the metering information to be seen. The Speed Finder had a rotation feature. This had an arrangement of prisms such that it could be swivelled between eye-level and waist-level positions. It also allowed the entire finder image to be viewed from 60 millimeters away and was suggested for use when wearing goggles or anything else that could prevent the user from placing the eyepiece right up to their eye. It allowed full metering. The Booster T Finder and Servo EE Finder were both essentially variations on the standard eye-level finder. The Booster T Finder contained an ultra-sensitive metering cell