A single-lens reflex camera (SLR) is a camera that typically uses a mirror and prism system (hence "reflex", from the mirror's reflection) that permits the photographer to view through the lens and see exactly what will be captured. With Twin lens reflex and rangefinder cameras the viewed image could be significantly different from the final image. When the shutter button is pressed on a mechanical SLR the mirror flips out of the light path, allowing light to pass through to the light receptor, allowing the image to be captured.

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