Jessmica
TPF Noob!
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Wow, this is so helpful! My college tutors really sucked at explaining all of this
Thanks
Thanks
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Regarding 18% grey, the term is derived, I believe, from the approximate percentage of black pixels/dots that need to be present on a white media (say, paper) for our eyes to perceive it as a mid-tone, neutral grey.
Grey Card - grey coloured card that uniformly reflects 18% of the light which falls upon it, used to calibrate exposure.
We know that a gray card will meter the same as a black and white checkerboard.
Yes. I've verified that experimentally. I admit it's a surprising result. By the way, if you want to verify it yourself make certain that the black squares are maximum black, Zone 0, or you'll find the the checkerboard reflects more than a gray card.We know that a gray card will meter the same as a black and white checkerboard.
Do we?
Precisely. As I pointed out, it leads to paradoxical conclusions, meaning either that the assumptions are wrong or that there's a non sequitur in the argument. We need to find where it breaks down. I don't think the checkerboard axiom is it.Anyway your argument is flawed.
External light meters measure luminous intensity, usually in some ad hoc units. Most then provide a circular slide rule devised to calculate, for a given film speed, a combination of shutter speeds and apertures which will give a medium gray negative. Internal meters have a linkage to the camera's workings which do the same thing automatically. Sans the slide rule or the linkage, light meters simply measure luminous intensity. (Actually, they don't measure luminous intensity as the SI defines it, but for our purposes here the difference is so trivial that I won't go into it.)A light meter in a camera is calibrated to render what it meters medium grey (usually around 18% reflectance).
But, complicated or not, if a concept is inconsistent with the Zone system then either the concept or the Zone system is wrong. Since the Zone system has been working since 1940 it's more likely that the concept is wrong. The concept, in this case, is the idea that a gray card has 18% reflectance.You are over-complicating when talking about the zone system.