Twin lens reflex TLR cameras

Some rollfilm cameras are designed as twin lens reflexes. As Figure L.2 shows, the camera body has two lenses - one for viewing and focusing, the other for shooting. The upper or 'viewing' lens reflects off a fixed mirror and forms an image on a ground-glass screen on top of the camera. The lower lens is the one which takes the photograph, and is fitted with a shutter and a diaphragm within the lens. To use a TLR camera you load it with a rollfilm, set shutter speed and f-number according to the light, and then look down onto the focusing screen to see what you are photographing.

Turning the focusing knob moves both lenses backwards and forwards, so that when your subject is sharply imaged on the ground-glass screen the taking lens is also correctly positioned to give a sharp image on the film inside the camera. Pressing the release fires the bladed shutter, exposing the picture. The image on the focusing screen does not disappear at the moment of shooting like a single lens reflex. It is easy to shoot from low viewpoints and still see to focus. However, since viewing and taking lenses are separate, the camera suffers parallax error (page 32) especially in close-up work. It is also bulky, and you lack the ability to change lens focal length. The picture on the focusing screen appears reversed left to right - irritating when trying to follow a moving subject.

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