Inside a single-lens reflex camera A. Body. The light-tight box that contains the N. Film advance. A lever that advances an unexposed camera’s mechanisms and protects the film segment of film. Some cameras advance film automatically. from light until you are ready to make an exposure. B. Lens. Focuses an image in the view O. Shutter-speed dial or button. Selects the shutter speed, finder and on the film. the length of the time the shutter remains open. On some models, it also sets the mode of automatic exposure operation. C. Lens elements. The optical glass lens P. Shutter release. A button that activates the exposure components that produce the image. sequence, in which the aperture adjusts, the mirror rises, the shutter opens, and film is exposed. D. Focusing ring. Turning the ring focuses the image by adjusting the distance of the lens from the film plan. Some cameras focus Q. Hot shoe. A bracket that attaches a flash unit to the automatically. camera and with suitable units provides the electrical linking that synchronizes camera and flash. E. Lens diaphragm. A circle of overlapping R. Rewind mechanism. A crank that rewinds the film into its leaves that opens to increase (or closes down cassette after the roll of film has been exposed. Some to decrease) the amount of light reaching the cameras rewind the film automatically. film. F. Aperture ring or button. Setting the ring S. Film cassette. The light-tight container in which 35mm film or button determines the size of the is packaged. diaphragm inside the lens. G. Mirror. During viewing, the mirror reflects light from the lens upwards onto the viewing screen. During an exposure, the mirror swings out of the way so light can pass straight ahead to the film. H. Viewing screen. A ground-glass (or similar) surface on which the focused image appears. I. Pentaprism. A five-sided optical device that reflects the image from the viewing screen into the viewfinder. J. Metering cell. Measures the brightness of the scene being photographer. K. Viewfinder eyepiece. A window in which the image from the pentaprism is visible to the photographer. L. Shutter. Keeps light from the film until you are ready to take a picture. Pressing the shutter release opens and closes the shutter to let a measured amount of light reach the film M. Film. The light-sensitive material that records the image. The film speed (the rating of a particular film’s sensitivity) is set into the camera by turning a dial, or, on some cameras, is set automatically when you load the film.