Olympus E-PM2 Actual ISO vs IS0 set in camera?

tinternaut wrote:

It would help if ISO themselves put some input into the issue, such that correct exposure is predictable, given an aperture and shutter speed, from one digital camera to tbe next. Sensitivity has been abused too long.

Well, correct exposure is in general predictable based on camera ISO as long as you define correct exposure in the traditional way. If you meter for middle gray, middle gray will come out right.

However, in the digital age, for those of us who shoot RAW and aim for minimal noise but with those highlights preserved that we care to preserve, metering for middle gray is inferior to metering for the highlights. An efficient way to do that with Oly cameras is by means of the live view blinkies. An alternative available on any modern MFT camera is the live view histogram. A third way is to use the spot meter, meter on the highlights, and then dial in appropriate EC based on that highlight reading. What is appropriate here depends on the DxO "measured ISO". On my old G1, whose "measured ISO" is about 1/3 EV higher than the camera ISO, I would dial in about two stops. On my E-M5, whose "measured ISO" is about one EV lower than the camera ISO, I would dial in 3.3 stops.

As for what Olymous is doing, I'm happier with it since they moved to the Sony sensor. With tbe 12mp sensor, I was able to get good (if less predictable) results with ETTR and experimenting with the raw files.