A rangefinder camera has a viewfinder that is separate from the taking lens. Its focusing system, called a rangefinder, is linked to the focusing ring of the lens.
In the center of the viewfinder you see two images of the subject, one on top of the other. When you turn the focusing ring, one image moves. When the two images line up exactly, the subject is in focus. Rangefinders are small and quiet, and many street photographers like them. Because the viewfinder sees a slightly different view from the lens, close subjects can show parallax error. Leica M cameras still use this system today.
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