Jorge
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- Sep 6, 2002
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There is a little bit of misinformation here that I think needs to be clarifed. The BTZS does not assume there is a 5 stop range of low contrast subjects.
The reason is simply explained in Phil's book and has to do with the reproduction ratio of printing materials. With few exceptions the maximum SBR that can be reproduced is 5 stops. So given this reproduction value we can say that no subject that we intend to photograph can have less than a 5 stop range if we are to get detail in the important areas.
Phil then deduced that if we add this 5 stop reflectance range to the contrast difference in an illuminance measurement, we could then estimate the total subject brightness range.
Of course, Phil explains it much better and in more detail in his book, but there is actually no assumptions made for the basis of his system. Some knowledgeable people argue that he does do a little of data massage in the flare factors, and strictly speaking they are correct. But I cannot argue with success, it works for me.
The reason is simply explained in Phil's book and has to do with the reproduction ratio of printing materials. With few exceptions the maximum SBR that can be reproduced is 5 stops. So given this reproduction value we can say that no subject that we intend to photograph can have less than a 5 stop range if we are to get detail in the important areas.
Phil then deduced that if we add this 5 stop reflectance range to the contrast difference in an illuminance measurement, we could then estimate the total subject brightness range.
Of course, Phil explains it much better and in more detail in his book, but there is actually no assumptions made for the basis of his system. Some knowledgeable people argue that he does do a little of data massage in the flare factors, and strictly speaking they are correct. But I cannot argue with success, it works for me.