Aperture Control
Most SLR cameras provide automatic aperture control, which allows viewing and metering at the lens’s maximum aperture, stops the lens down to the working aperture during exposure, and returns the lens to maximum aperture after exposure. For perspective-control and tilt/shift lenses, the mechanical linkage is impractical, and automatic aperture control was not offered on the first such lenses. Many PC and TS lenses incorporated a feature known as a “preset” aperture, which lets the photographer set the lens to working aperture, and then quickly switch between working aperture and full aperture without looking at the aperture control. Though slightly easier than stopped-down metering, operation is less convenient than automatic operation.
When Canon introduced its EOS line of cameras in 1987, the EF lenses incorporated electromagnetic diaphragms, eliminating the need for a mechanical linkage between the camera and the diaphragm. Because of this, the Canon TS-E tilt/shift lenses include automatic aperture control.
In 2008, Nikon introduced its PC-E perspective-control lenses with electromagnetic diaphragms. Automatic aperture control is provided with the D300, D3, D700, and D4 cameras. With some earlier cameras, the lenses offer preset aperture control by means of a pushbutton that controls the electromagnetic diaphragm; with other earlier cameras, no aperture control is provided, and the lenses are not usable.
Read more about this topic: Perspective Control Lens
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