Interchangeable lenses are not unique to single lens reflex cameras, of course. Film cameras that use optical viewfinder windows (called rangefinder cameras), such as the Leica, also have interchangeable lenses. Early in my career I used a Mamiya twin lens reflex camera, which allowed unhooking both lenses (one for viewing, one for taking the picture) [...]

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The next most important component of a digital SLR is the lens-or, more properly, lenses- because, unlike other types of digital cameras, the lens of a dSLR is interchangeable. Galileo and Leeuwenhoek came up with improved telescope and microscope gadgets, and most of the optical breakthroughs hence have involved different kinds of shapes of glass [...]

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Digital cameras have shutters, too. They can have either a mechanical shutter, which opens and closes to expose the sensor, or an electronic shutter, which simulates the same process. Many digital camera have both types of shutter, relying on a mechanical shutter for relatively longer exposures (usually 1/500th second to more than a second long), [...]

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