Automatic aperture

AUTOMATIC APERTURE - An automatic aperture remains fully open until the shutter is released, at which time it closes down to the pre-set aperture size in order for the picture to be properly-exposed. An automatic lens has an automatic aperture.

Automatic aperture - lens aperture mechanism that stops down to s preset size just as the shutter is fired, afterwards returning to the maximum aperture again for focusing and composing the next image.

A lens with an automatic aperture diaphragm that can be kept wide open, at its widest aperture, until the shutter is released, regardless of the aperture setting for the exposure.

For some lenses, including a few long telephotos, lenses mounted on bellows, and perspective-control and tilt/shift lenses, the mechanical linkage was impractical, and automatic aperture control was not possible.

In the beginnings of exposure automation (ca. 1960) the instruments were even used for setting exposure settings directly, mainly for automatic aperture setting.

Additional steps may include automatic aperture operation and film advance by motor drive. Compare this to analogous sequence in SLR cameras you may imagine why RF and SLR are such different animals.

With older automatic cameras, or today's LEICA or Mamiya etc., choose your automatic aperture on the camera, and set the flash for one-stop wider. Now you'll get fully automatic exposure and fully automatic fill-flash. Wow!
If lens is set to ...

Available with nearly all digital cameras, exposure compensation works perfectly in Program (P) mode and in the semi-automatic Aperture Priority and Shutter Priority modes.

(If you want, you can leave the camera in the automatic aperture-priority mode for this exercise, too). Write down that shutter speed.

Automatic lens
Lens which remains at full aperture no matter what working aperture is set to, until the shutter is released. This allows finest focusing, without affecting metering. Also known as 'Automatic aperture'.
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See also: Meter, Automatic, Aperture, Focus, Camera