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Subject: Re: Exposure to the right and tone placement





that's because the meter isn't well-suited to digital because it's calibrated
to 12% reflectance, which is all the way down at the 12% level in a linear
capture.




Bruce,

Just because the meter is calibrated for 12% doesn't mean you can't do your own calibration just like Ansel Adams did in his time by exposing a gray card in increments of one stop. As you know, a gray or white card exposed according to the meter reading will give an equivalent of 12% in the picture, corresponding to a pixel value of about 97 in aRBG or 31 and 492 in 8 and 12 bit gamma 1 space respectively.

If you add 3 stops to the indicated exposure, the resulting tone should be 96% or near pixel value 3932 in the raw linear space, which is about where you want to place the highlight and close to the compensation value you quote for your Minolta spot meter. In zone system nomenclature, this is placing the tone at Zone VIII and is what I understand you are doing.

With my own camera, I exposed a gray card with various exposure compensations in half stop increments and decrements and plotted the resulting pixel values graphically and determined graphically when clipping occurs. If I expose a highlight according to the meter reading plus 3 stops, it is placed very near to 4096 in the linear raw file, which I understand is what you recommend.



My old Pentax 1 degree digital meter (the same one shown by Adams in the 1981 copy of The Negative, p 63) works just fine for this purpose.

If readers wish to work with the raw data directly one can convert into 16 bit linear space with dcraw (do a Google search) or another raw converter allowing such conversions and examine the raw values with Photoshop (to get 12 bit values, first normalize the PS 15+1 eyedropper reading to 1 by dividing by 32768 and then multiply by 4096 to get the 12 bit value)

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