Proper Blind Exposure with a Gray Card

Started Nov 12, 2012 | Discussions thread
panos_m
Senior MemberPosts: 1,217
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Re: The Crux of the Matter
In reply to Jack Hogan, Nov 12, 2012

Jack Hogan wrote:

panos_m wrote:

If "proper blind" exposure is that I obey the spot meter reading with the goal to reproduce the gray of the reflectance card then I need a card with the same reflectance the particular camera spot meter reads. That is different for my two cameras and obviously not 18%.

Let's assume that your camera manufacturers, knowing their sensors well, chose a good compromise for where a mid-tone should be recorded in the range of possible raw values (10.2% of full scale for the D3 and 12.5% for the GF1).

Ok.

No matter what reflectance card is placed in front of their meters, each of them will always record them as the designed mid-tone. So wouldn't you want to meter off a middle gray card to ensure that it be recorded as a mid-tone, therefore ensuring that the rest of the scene is also consequently 'properly' exposed?

If I meter a 18% card with the GF1 for example it will render it as 12.5%. If I want to render it as 18% I will have to add 3.0 - 2.47 = 0.53 stops of positive exposure compensation.

And why on earth would anybody (anybody!) want to use a 12% card in this context?

If I meter a 12% card it will render it as 12.5% and in accordance all other tonal values (including 18%) will be almost in place.

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Panagiotis

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