Working aperture measurement
The working aperture is in the photograph , the measurement of light in the F-number , which is also used at the next recording.
The light conditions are measured by measuring the working aperture of single -lens reflex cameras with the lens stopped down (closed on the preselected aperture), while with the aperture open it is focused (focused). Most cameras have a button that mechanically closes the aperture to the preselected value and at the same time electrically activates the exposure metering. The measurement result is displayed with a display instrument, usually designed as a light balance , and reflected in the viewfinder image .
With some viewfinder cameras, such as the Minox-35 series, the working lumbar measurement is simulated by means of a suitable dimming of the lens-parallel exposure cell.
The working aperture measurement is the forerunner of the open aperture measurement , which was only developed in the mid- 1960s . The advantage of this working aperture measurement with single-lens reflex cameras is that, in addition to the correct exposure, the depth of field of the image can also be assessed as a result of the closed aperture. Many cameras allow both measurement methods.
The open aperture measurement requires a correct simulation of the light intensity used for the recording. The option of open-aperture measurement was one of the most powerful sales arguments for appropriately equipped SLR cameras in the 1970s . Cameras equipped for open aperture measurement initially always had a aperture button for depth-of-field control, but this was often rationalized away in simpler models and especially in modern cameras with autofocus .