Stop-down metering

If manual lenses are used on modern CSCs, the aperture has to be closed (stopped-down) to the desired value manually. This is would darken the viewfinder, but an electronic viewfinder compensates this disadvantage. 
The alternative is to stop-down the aperture only when the shutter is released and the photograph is taken (open-aperture metering).

Recommended links: Camerapedia, MIRWikipedia

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