Adox CMS 20 II

CMS 20 II is not a general-purpose film. Adox markets it openly as a micrographic emulsion: the silver halide crystals are small enough and the resolving power is high enough (around 800 line-pairs per millimeter under ideal conditions) that the film is used for document copying, scientific imaging, and fine-art contact work. For photographers who need it, it is the closest current replacement for Kodak Technical Pan, which Kodak phased out between late 2004 and mid-2005.

The ISO 20 rating is accurate in normal development, but the film is designed to be used with Adox's own Adotech IV developer (the current partner to the CMS 20 II emulsion; Adotech III was the prior version), which is specifically formulated to control the extreme contrast this type of emulsion produces. In conventional developers like D-76 or Rodinal, CMS 20 II goes contrasty very fast and loses the shadow detail that makes it useful. In Adotech IV at the recommended dilution and time, the contrast is tamed to something closer to a normal pictorial curve, and the resolution becomes almost hallucinatory: fine textures in subjects like stone, fabric, or bark are separated in ways other films flatten out.

Sharp lenses are necessary to get any benefit from the resolving power. The film will show the limits of an average lens before it shows its own limits.

Available in 35mm and 120. Adox also lists sheet film sizes for large-format scientific use.

Reciprocity exponent is 1.0, which is unusual. Reciprocity behavior on CMS 20 II is gentler than most slow films, but it is not truly linear: Adox's datasheet calls for roughly half a stop at a metered one second and more at longer exposures. Zone Light Meter treats it accordingly and does not apply correction past the one-second threshold. For the lab or studio work this film is typically used for, that simplicity is one less variable to manage.