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

Started Aug 17, 2014 | Discussions thread
OP Leo Veteran Member • Posts: 6,445
Re: Olympus E-PM2 Actual ISO vs IS0 set in camera? -my TEST

I have photographed xRite color checker 24 card with seven exposures stepping by +1/3EV:

0EV, +1/3EV, +2/3EV, +1.0EV. +1 1/3EV, +1 2/3EV, + 2.0EV

Then I have opened the images in LR and with expose slider adjusted the brightest Gray to 94.5 each image. Then I have verified the same color patch for all images (yellow). Its R, G and B reading were about the same up to +1.7EV. At the +2.0EV I had to adjust exposure control more negative. The adjustments were exactly:

0EV, -1/3EV, -2/3EV, -1.0EV. -1 1/3EV, -1 2/3EV.

The yellow patch R,G,B numbers were read as 90.7, 87.7, 37.6

The brightest gray patch showed that it is overexposed (red). At exposure -2.0EV the this patch reading were 97. 97, 97. I had to adjust exposure slider to -2.5EV to make the same reading = 94.5, however the whole image became little darker and the R, G and B for the yellow patch changed to: 87.7, 84.1 31.0. The overexposure red marking disappeared.

My conclusions from this test are:

1) I am underexposing routinely approximately -1.7EV.

2) The underexposure marking (red) is a good indicator and it well correlated with the RAW format.

Any suggestions?

Leo

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