Difference between revisions of "Open-aperture metering"
(in contrast to stop-down) |
(rephrase, as early Topcon, Nikon had OAM alongside other brands' stopdown method) |
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| − | The phrase "open-aperture metering" contrasts with | + | The phrase "open-aperture metering" contrasts with a less advanced, [[stop down | stopdown]] metering scheme, used in many early [[SLR]]s to offer [[TTL]] exposure readings. In open-aperture metering, a linkage at the rear of the lens communicates the currently-selected f-stop to the camera's exposure meter, while leaving the lens at its widest aperture for a bright viewfinder image. This lets the meter weigh the amount of dimming which will occur as the diaphragm closes to the selected aperture. (An [[automatic aperture]] then stops down in the instant before the shutter opens.) So unlike stopdown metering, there is no need to have the viewfinder inconveniently dim while taking meter readings. |
| − | Open-aperture metering has been standard for SLR and DSLR cameras since the mid-1970s. Earlier SLRs (notably, ones using [[42mm screw lenses]]) may be assumed to lack open-aperture metering, although there are exceptions. | + | Open-aperture metering has been standard for SLR and DSLR cameras since the mid-1970s. Earlier SLRs or budget models (notably, ones using [[42mm screw lenses]]) may be assumed to lack open-aperture metering, although there are exceptions. |
Latest revision as of 14:09, 30 January 2023
The phrase "open-aperture metering" contrasts with a less advanced, stopdown metering scheme, used in many early SLRs to offer TTL exposure readings. In open-aperture metering, a linkage at the rear of the lens communicates the currently-selected f-stop to the camera's exposure meter, while leaving the lens at its widest aperture for a bright viewfinder image. This lets the meter weigh the amount of dimming which will occur as the diaphragm closes to the selected aperture. (An automatic aperture then stops down in the instant before the shutter opens.) So unlike stopdown metering, there is no need to have the viewfinder inconveniently dim while taking meter readings.
Open-aperture metering has been standard for SLR and DSLR cameras since the mid-1970s. Earlier SLRs or budget models (notably, ones using 42mm screw lenses) may be assumed to lack open-aperture metering, although there are exceptions.
