Foma’s Fomapan line is among the least expensive panchromatic films still in production, which makes it a common entry point into traditional black-and-white work. Two characteristics complicate its use: the effective speed that yields full shadow detail often sits below the rated value, and the emulsions suffer pronounced reciprocity failure in long exposures. The films differ in emulsion technology: Fomapan 100 Classic is built on a traditional cubic-grain silver-halide structure, while Foma describes Fomapan 200 Creative and Fomapan 400 Action as tabular-grain (“T-grain”) emulsions. Despite that, all three show steep reciprocity corrections in long exposures.

Box speed versus metered speed

Foma rates the three Fomapan emulsions at ISO 100/21°, ISO 200/24°, and ISO 400/27° respectively. These figures follow the ISO standard, which fixes the speed point at a defined density above base-plus-fog. The standard does not guarantee that every part of a scene’s shadow range is reproduced, and with these emulsions the deep-shadow values frequently fall onto the toe of the characteristic curve, where they record with little separation.

In practice, many photographers expose Fomapan films at roughly one stop below the rated speed, rating Fomapan 100 at EI 50 to 64 and Fomapan 200 nearer EI 100 to 160, to lift shadow detail clear of the toe. The ISO figure is correct by the standard, but for these films it tends to place the speed point closer to the threshold of usable shadow detail than many photographers prefer.

Reciprocity failure in long exposures

Reciprocity failure is the breakdown of the assumption that halving illumination and doubling time yields equal density, occurring when exposures grow long and light levels low. All silver-halide films exhibit it, but Foma’s datasheets describe an unusually steep correction. For Fomapan 100, the datasheet calls for roughly one additional stop at a metered one second, about three stops at ten seconds, and four stops near one hundred seconds. Fomapan 200’s published table is the steepest at short metered times, asking about 1.5 stops at one second, then converging on the same three- and four-stop figures at ten and one hundred seconds; Fomapan 400 needs the least correction of the three.

Because the correction grows non-linearly, a small metered time can expand dramatically: a metered ten seconds for Fomapan 100 becomes roughly eighty seconds of actual exposure. Many practitioners report that beyond a few seconds the datasheet figures overcorrect, and treat the published curve as a conservative upper bound rather than an exact prescription.

Why the emulsions behave this way

Reciprocity failure arises because silver-halide crystals form latent-image specks less efficiently at low light intensities, so a larger fraction of absorbed photons fails to produce a developable image as exposure lengthens. The effect is most pronounced in Fomapan’s cubic-grain emulsion, but Foma’s published corrections remain steep even for its tabular-grain films. The same toe characteristics that recommend generous shadow exposure at normal light levels also steepen the reciprocity correction in dim ones, which is why Fomapan’s two quirks tend to appear together.