> Call me what you want...
Ooo, the temptation. <smile>
> I understand the theory of it and know what to look for, but I
> don't see it and I am sorry. Is there a place on the net that
> can illustrate the toe and shoulder as opposed to the digital
> absence of it?
You can go to the Ilford site and look at the PDF for the B&W
films under the Products section. There is a characteristic
curve for each film. That's a start.
Let me illustrate with the following 14-stop brightness scale:
Subject Film Digital
Brightness Records As Records As
---------- ---------- ----------
14 11.0(shoulder) 10.0
13 10.7(shoulder) 10.0
12 10.3(shoulder) 10.0
11 10.0(shoulder) 10.0
---10------------9.5(shoulder)----10.0----(white)
9 8.7(shoulder) 9.0
8 8.0 8.0
7 7.0 7.0
6 6.0 6.0
----5------------5.0---------------5.0----(middle gray)
4 4.0 4.0
3 3.0 3.0
2 2.5(toe) 2.0
1 2.0(toe) 1.0
----0------------0.0---------------0.0----(black)
Now for the interpretation. The above scale (utilizing a
variation of the zone system where each number represents a
doubling in brightness shoes how digital and film respond
differently in the extremes. Starting from the bottom, black is
black as recorded by film and digital. A "near black" tone will
normally capture correctly in digital, but will either drop to
black (inverted or no toe) or will raise in capture value
slightly (toe) on film. By the time we get to the mid-tones,
film and digital are pretty uniform, but variances in
sensitivity to different colors are what make each film
different. By the time we get to 10, we're usually at the point
where we've maxed out the ability of digital to capture any more
detail. Anything beyond this brightness will be recorded with
the same brightness level (100% saturation). Film, however,
tends to desensitize as it nears saturation. You can see where
in the above illustration the high values start to compress and
become non-linear.
In practice, we B&W film photographers utilize this toe and
shoulder region to preserve slight details in the highlights and
shadows which would normally be lost (pure black, pure white).
Why not just sqeeze the entire scale to extend the sensitivity
to a full 14 stops (in the above illustration) and keeping it
linear? Because the viewer would be disturbed by the lack of
realistic tonal seperation (one stop=one stop) in the mid-tones.
As you can see with the illustration, we can apply custom curves
to a digital file to mimick "shoulder" and "toe", but it's doing
so on a far reduced subject brightness range. In the
illustration, the film is capturing 14 stops of data whereas
digital is capturing 10 stops. Film isn't linear on the ends of
the sensitivity range, but it is capturing some detail far
beyond the brightness range that digital is able to.
AG
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