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Just to expand on Matt's answer a bit. Most B&W films used during the first half of the 20th century were not panchromatic. They were much more sensitive to the energy in blue light than the energy in red light. Even if a panchromatic film were used, if a blue filter were placed in front of the camera's lens, it would reduce the amount of red light ...


Photo films and digital sensors do not record colors exactly as seen by our eye / brain vision system. Initially, photo films were only sensitive to the violet and blue region of the visual spectrum. Translated, films blackened when exposed to violet and blue. They did not blacken when exposed to any other colors. The resulting black & white prints ...


Are any of these in the ballpark? The last one: "imperfect chemical film response". Most black and white processes are not "panchromatic". That is, it does not respond the same way across the whole color spectrum. Ever see darkroom with a red "safe light"? That's what's going on here.

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