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Subject: Re: raw 3.1 professional custom profiles for highend digital cameras



John,

As far as I can determine, the D70 (which is what I use) is calibrated to the ANSI standard equivalent of 12% reflectance. This means that if you use the spot meter and normal post processing, the metered area will be rendered as 12% gray. If the subject is 12% gray, it will be reproduced accurately. However, if you are metering from snow, the rendering will appear dark. Ansel Adams places normal Caucasain skin in zone VI, one stop brighter than 18% gray and 1.5 stops above 12% gray and positive exposure compensation is needed here too. On the otherhand, if you are photographing a black cat, you will have to give less exposure than indicated by a spot metering from the animal. It may seem counterintuitive that positive compensation is needed if you meter from light objects and the converse for dark objects. If you are technically minded, I would suggest you visit Norman Koren's web site for a rigorous scientific discussion of these matters. This site was just recommended by PhotoshopNews.com (even though Nor
man does not use PS)



The digital sensor is linear in its response to light and once you place one tone with your meter, all the others will fall in place and the proper tone balance will be maintained. If you goof in the placement and the image is underexposed, you can use the exposure adjustment in ACR, which linearly moves all values to the right in the histogram. If the shadows are not clipped, you will usually get an acceptable result, but as Bruce points out you may get noise and posterization in the shadows and the results are not optimal. If you do overexpose and clip the highlights, you can often recover them in ACR as Bruce has explained.

As an aside, the D70 and other Nikon cameras tend to "underexpose" according to the concepts expressed in this thread and this has been discussed extensively in the Nikon threads of DPReview. Nikon apologists say this is to protect the highlights from blowing out, but this is counter to the concepts being discussed here. Always check your histogram and give enough exposure so that the right of the histogram is well populated. The histogram and the blinking highlights tend to say there is overexposure when there is in fact none, but if you use the histogram as a guide, you will avoid the worst underexposure.

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