For film cameras, holding exposure time times f-stop constant does not produce the same image density.
Exposure time for film is not straight photon integration, like it is for a CCD array. You can only trigger each film grain once, but new photons can repeatedly add electrons to a single CCD pixel. So there's what's called "reciprocity failure".[1]
For film cameras, holding exposure time times f-stop constant does not produce the same image density. Exposure time for film is not straight photon integration, like it is for a CCD array. You can only trigger each film grain once, but new photons can repeatedly add electrons to a single CCD pixel. So there's what's called "reciprocity failure".[1]
[1] https://en.wikipedia.org/wiki/Reciprocity_(photography)