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 comparison. 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.
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