DiMAGE A2 Exposure Reliability

My test results showed unexpected variations of image intensity that implied errors of exposure. My first reaction was to blame myself, and to be as meticulous as possible in metering exposures, assuming that the camera itself is precise and accurate. I am now questioning the camera; so far the results suggest that the camera's metering system may mis-expose by up to 1.5 stops.

Metering technique. My early tests were done by holding the camera close to a middle-gray target, setting the exposure dial on "A" to use aperture priority, press the shutter button halfway down several times while moving the camera slightly, and observing the shutter speeds that were called for. When I achieved consistently the same shutter speed with repeated measurements of the target, I moved the exposure dial to "M" (manual) and adjusted the f-stop and shutter speed to the values shown when it was set to "A".

When the results using this were inconsistent, I set the camera to use spot metering, and used the viewfinder to ensure that the camera was aimed at the middle-gray target, and took repeated readings as before.

The results:

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