Quoted By:
Let me see if I understand "stop down metering" correctly:
Point: on some lenses the aperture remains wide open until the time of taking the photo no matter what aperture the user has selected.
Point: the lens communicates with the camera this information about the aperture so the camera will receive correct metering information
Point: if this data link is broken then photos will be underexposed due to the camera assuming the aperture is wide open when it is not
Point: to compensate for this the user must use the depth of field preview button on the lens to temporarily get a light metering with the correct aperture, and set their shutter speed/exposure appropriately
Final point: this is NOT necessary on vintage lenses that simply narrow the aperture all of the time when the aperture selection ring is turned. This physically limits the amount of light going through the lens all of the time and thus the camera will take the correct reading with no further action necessary
Is -any- of that right?
