I herewith will try to shed a light on the discussions of film B&W vs. digital B&W from -a little- engineering point of view; with as simple terms as possible.
First the Sensitivity vs. Wavelength of the recorded spectrum of visible light. In the below illustrations please note that the vertical axis is always Sensitivity for film or Quantum Efficiency for sensor- meaning almost the same- and the horizontal axis are the visible color wavelengths in nanometers.
First let's see how a hi-speed
panchromatic film HP5+(thicker silver-halide spread over the surface for longer tones & longer exposure latitude; for digital this is equivalent of Dynamic Range) also an
orthochromatic film APHS Litho(limited bandwith for solely hi-contrast applications ) will react to the visible spectrum.
Please note how the HP5+ reacts to different wavelengths and the respective colors in nanometers too.
To simplify the view the HP5+ alone:
The Tri-X curve now:
Note how the two top films cover the spectral range with their characteristic responses to colors. (Both exhibit excellent responses, do not mind about the cut-off frequency in testing the Tri-X.. the HP5+ is more linear/balanced while the Tri-X is more "blues loving"
😀 )
How about a CCD sensor from the Leica M9 neighborhood? (16MP) First the curves for individual colors. Note the "discrepancies" and how CFAs (color filter arrays) affect the sensitivity responses for each color:
Do they look any similar to the HP5+ or Tri-X color response curves above? (Hardly.. )
Bear in mind that ANY sensor, CCD or CMOS, is monochromatic by construction, it's the array filters that turn the "assigned" cells into color-sensitive ones with some sacrifices from the sensitivity too. The following is the ACTUAL response of the same CCD sensor above with no-CFAs (i.e. similar to the one the new B&W M-Leica is going to have):
Now you can compare this curve to the ones of the HP5+ and the Tri-X.
Shortly:
- We still need years to duplicate the characteristics of silver halides crystals following the chemical reactions as seen on the film through digital means.
- The more silver halide involves with further chemical reactions (film developing + image developing on paper thru wet printing) the more the differences between these characteristics curves.
Regards,
Bob