> Based on his darkroom experience, AG wrote about the behaviour
> of the E-sensor compared with analogue imaging, and mentioned
> the "shoulder" and ?? I forget, the "heel".
> For the sake of one who unfortunately has no darkroom
> experience, could you please elaborate, AG?
A scene as captured by a sensor will have five distinct
brightness levels of which I'll refer to in this response:
Pure White
Light
Midtone (average brightness, 18% grey, etc.)
Dark
Pure Black
Assume for a second that we expose a scene for the midtone
exposure so that it is captured at exactly the same level on
color print film, slide film and digital capture. When doing
so, you will see the Light and Dark portions pretty well match,
except for the nuances which are "signature characteristics" of
a given film type.
Where the differences come in is in the transition between Light
and Pure White as well as Dark and Pure Black. For example:
Fujichrome Velvia has a hard transition between Dark and Pure
Black. There is no "toe" to the film, as anything below a
certain brightness value is pushed downward to black. However,
most print films have a gentle transition between Dark and Pure
Black. As the real life brightness level decreases, the film
isn't linear in the falloff and will continute to show something
down in the deepest of shadows. In essence, a print film with a
toe is pulling dark values up away from pure black. Digital is
between these two film types and attempts to capture a linear
response down to the point where sensor noise is the limiting
factor. Better cameras, such as the E-1, will fudge a fake toe
to give you the feeling of a gentler transition between Dark and
Pure Black, but it does so through the stretching of the
midtones.
So, as a general rule, "Toe" is the hockey-stick curve between
the "Straight-line Response Section" (or linear response) of the
film/sensor and the Pure Black.
The "Shoulder" is the opposite end of the spectrum. This is the
transition between Light and Pure White. Classic thick emulsion
B&W films would have a shoulder that went on forever. You could
keep detail in bright clouds while having your midtones in the
proper position. Again, digital cameras are pretty well linear
in reponse, but will fudge a slight shoulder to match film a
little bit.
AG
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