Agfa Isopan F

Isopan F was the fine-grain panchromatic film in the postwar Agfa B&W lineup, sitting between the ultra-slow Isopan FF and the medium-speed Isopan ISS. Period Agfa data sheets list it at 17 DIN, which translates to ASA 40 under the rating conventions of the time. Some later releases under the Agfa-Gevaert merger pushed it to ASA 50. The emulsion was cubic-crystal silver halide on an acetate base for 35mm and a slightly thicker base for the medium-format roll versions.

The characteristic look is dense midtones with a long shoulder and a slightly compressed toe, making it a good portrait and architectural film and a difficult choice for scenes with deep shadow. Compared with Kodak Plus-X of the same period the grain is tighter and the highlights compress earlier. Compared with Ilford FP3, the rendering runs cooler and the curve sits flatter through the mid-tones. Press shooters preferred it for studio and controlled-lighting work, switching to Isopan ISS when they needed more shutter speed.

Development in Agfa Rodinal at 1:50 gives a clean negative with the cubic grain visible but not aggressive. Rodinal 1:100 stand for an hour brings out a compensating curve that helps if you metered for the shadows. Microdol or D-23 produce tighter grain at the cost of a half stop of effective speed.

The film was phased out by the end of the 1970s as Agfa-Gevaert thinned its B&W catalog; precise end dates vary by region and format. Sealed boxes still turn up in estate sales, mostly in 35mm and 120 with the occasional Karat or 127 cartridge. Freezer storage helps. Warm-stored rolls past about 1985 carry visible base fog no developer trick can fix.

Reciprocity exponent is 1.33. Zone Light Meter applies the correction past one second. A metered 30-second exposure becomes about 100 seconds at the negative, which puts long-exposure work firmly into territory where you need to bracket. For interior architectural shots at small apertures, the meter reading is the start of the calculation, not the end.