This developer is intended for use with T-Max and Delta films, although it will produce excellent results with traditional emulsions. FX37 is designed to produce very sharp, tonally rich negatives with an EFS speed increase (½ – ⅔ of a stop).
It is not a fine grain developer and is not recommended for fast traditional films.
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FX37 is the closest published formula to FX39. The benzotriazole can be eliminated if the bromide is increase to 1 gram:
The only difference between this and the original FX37 formula is the increase of potassium bromide from 0.5 grams to 1 gram and the consequent omission of benzotriazole, which is difficult to dissolve — a move to help the amateur. That chemical was originally included for the conditions of professional reuse as fog levels can rise. The change has no effect on image quality.
—Geoffrey Crawley in Amateur Photographer 15 Oct 2005
Develop for 4–8 minutes at 20°C.