U of S | Mailing List Archive | alt-photo-process-l | Re: 3200 SHEET FILM? was Re: Ilford developers

Re: 3200 SHEET FILM? was Re: Ilford developers

Faster speed films have progressively shorter shelf life
because of their increased sensitivity to radiation. This is
mostly the inherent property of the emulsion grain and not the
development method. A real 3200 speed color film would be
affected by this effect very fast, while push processing 400-
or 800-speed b&w films would be influenced from this effect
much less.

Pictorial film speed ratings are determined by the sensitivity
to visible light. This sensitivity is typically greatly
enhanced by maximally taking advantage of spectral
sensitization. This is usually done by densely placing
sensitizing dye molecules on the surface of each crystal,
while maximizing the surface area to volume ratio of each
crystal (e.g., thin tabular grain). This way, the light
sensitivity goes up with the surface are of the crystals, up
to a certain soft limit. Above this soft limit, the efficiency
goes down and the sensitivity doesn't grow as fast with
increasing surface area.

Note that, when compared within same ISO speed rating groups,
color emulsions use much bigger crystals because each color
layer receives only about 1/3 of the white light.

On the other hand, the sensitivity to radiation is unaffected
by the dyes or the surface area of each crystal. This
sensitivity is largely determined by the crystal volume, while
maintaining other variables fixed or properly scaled for fair

While larger crystal emulsion has some increase in sensitivity
to light, it gains more sensitivity to radiation and this is
the real challenge in making fast pictorial film with long
shelf life. This is particularly so in color films. Some
recent technology alleviates this problem by making each
crystal very sensitive to photoelectrons generated on or very
near the surface of the crystal and not very sensitive to
those generated deeply within the crystal. This is almost like
making emulsions of hollow-shaped crystals whose interior is
filled with rather insensitive material. Thanks to this,
today's 1600-speed color negative films have better shelf life
than old days (and much finer granularity).

I personally do not think good film holders are too leaky to
fast films, and most careful photographers would not have any
problem with them. I think the real reason is the very small
market. Cost of customer support can be very high for any
product that is too unique or atypical. The manufacturers do
not want the risk of damaging the brand by selling products
taht are difficult to use correctly (think about the majority
of people who would buy it just because the product looks new,
and gets frustrated). Fast films have terrible reciprocity
failure, as well, and they would not be very useful if the
exposure is longer than a few second.

However, I do like the way TMZ looks. TMZ and Delta 3200 have
more pronounced shoulder than most other films of 100-400
speed rating, and so these films tend to produce brighter
midtones and more gentle highlights.