I was wondering if anyone can help with using Tetenal Ultrafin for developing black and white film?

I use a Jobo 1520 Unitank to develop my film. The instructions on the Tetenal bottle are not clear to me on the inversion process. They have development times for some film stock for various dilutions e.g. 1+10. In this there are two columns labelled A and B. Further down there are values listed for inversion for A and B. However, it is not clear to me anyway how these should be applied and at what intervals?

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    – Zeiss Ikon
    Commented Sep 1, 2022 at 12:12

2 Answers 2


I must admit that the instructions from Tetenal are very hard to understand for a beginner, but the number in the A and B columns are obviously the development times for different agitation rhythms.

If you e.g. develop an Ilford FP4+ in a 1+10-dilution, you should either:

  • develop for 5 minutes and agitate your tank every 3 seconds or
  • develop for 8 minutes and agitate your tank once every minute

Even if it is not mentioned in the instructions, you should agitate continously at the beginning for at least 15, better 30 seconds to make sure that the emulsion is soaked evenly with developer. Numbers in bold represent the preferred combinations of dillution and agitation rhyhtm, the other numbers will also work, while combinations with a — in the respective column are not recommended at all.


It appears that the A and B values and the different columns of times are for different dilutions of the concentrate. The first column is for one part developer to ten parts water, the second for one to twenty, and the third for one to thirty.

Within each dilution column is the recommended number of 3-second inversions for each agitation cycle (under A) and the total development time (under B). As I read it, if you're developing FP4+ in the 1+10 dilution, you should develop for 8 minutes (at 20 C) with 5 agitations (taking 3 seconds each) at the top of each minute (most instructors would recommend continuous agitation for the first 30 or 60 seconds after pouring in the developer, however).

It's uncommon to see this agitation rhythm specified by film type and dilution for a developer; most (like D-76 or ID-11) separately specify a manufacturer recommended agitation method (like Ilford's 30 seconds on fill and two or three inversions every 30 seconds) and vary only the total time by film -- though some workers do claim that varying agitation changes the quality of development in some ways.


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