Adox CHS 25 (pre-II)

The original CHS 25 was a Fotokemika product sold under the Adox label, not a Schleussner-era Adox emulsion. Fotokemika in Croatia produced the CHS line using the 1950s Adox formulas they had been making as Efke since the 1970s, and CHS 25 was effectively a relabeled Efke KB 25 with Adox packaging. When Fotokemika shut down in 2012, the original CHS 25 went with it. The current CHS 100 II under the Adox name is a different film made in Germany.

What made the original CHS 25 worth seeking out was the silver content and the single-layer cubic emulsion. The grain at ISO 25 was tight enough that 35mm negatives held detail comparable to 4x5 sheets from the modern roster. Resolution numbers Adox published put the film around 160 line-pairs per millimeter at low contrast.

Spectral response cut off around 620nm, which is closer to orthopanchromatic than to a fully panchromatic modern emulsion. Reds rendered darker than you would expect from Tri-X or T-Max 100. Skin tones came out heavier in shadow. That is either a problem or an aesthetic choice. The look reads as period correct for anyone trying to match prewar or postwar European photography.

Available formats included 35mm, 120, and sheets from 4x5 through 8x10. The 35mm came on clear PET base, which made it sensitive to light piping if you loaded sloppily. Compared with current Adox CMS 20 II, the old CHS 25 had wider tonal latitude and a softer shoulder. CMS 20 II resolves higher but compresses highlights faster.

Develop in Rodinal 1:50 for tight grain with strong micro-contrast, or in ID-11 stock for smoother gradation at the cost of some apparent sharpness. The film also responded well to Diafine two-bath chemistry.

Reciprocity exponent is 1.33. Zone Light Meter applies the correction past one second. A 10-second meter reading becomes about 22 seconds at the negative; a 30-second reading extends to roughly 95 seconds. For tripod work in low light, which is where ISO 25 lives, the correction is constant and substantial.