Development times for the ADOX C-TEC 41 kit with AGO film developer

rlm · 2025-09-01T07:29:39+00:00

Hallo zusammen Wir arbeiten mit dem ADOX C-TEC 41 Developing Kit im AGO Filmentwickler (temperaturgesteuert). In der Anleitung ist angegeben, dass nach der...

rlm

Hello everyone We use the ADOX C-TEC 41 Developing Kit in the AGO film developer (temperature-controlled). The instructions state that, after the initial development, the times for each of the next two films should be increased by 15 seconds. In practice, however, we don’t always develop just two films per batch, but for example: [*]

sometimes 3 films together in the drum,
and occasionally 5 films at the same time.

[*] Our question: How does the time adjustment work in such cases? For example, the instructions indicate that there is already a 30-second difference between the 4th film (3:30 mins) and the 8th film. This corresponds to almost one stop of push development – which makes us unsure in practice whether this is correct for multiple development in a single drum. Does anyone have experience with this and can tell us whether the time correction is based on the total number of films developed, or whether a different recommendation applies for multiple development (several films at the same time)? Thank you very much for your help.

Wolfgg

Hello, Example: Five films are being developed simultaneously in fresh developer. Afterwards, the activity has dropped to such an extent that 2 × 15 seconds must be added for subsequent development. Assuming that the activity decreases linearly over time, the five films would be underdeveloped by exactly 15 seconds after 3 minutes 15 seconds (2 × 15 seconds / 2). So, with 5 films in fresh developer, you should set the time straight away to 3 minutes 30 seconds. In short: simply ask how much extra time would be needed for the last film if you were developing them all individually. And add half of that extra time straight away if they are all being developed at the same time. Regards, Wolfgang

Wolfgg

You can also solve the problem graphically, which makes it clearer. The diagram shows how the development time increases in line with the number of films being developed. The diagram below includes examples of how to use it. Suppose that initially only 1 film is developed in freshly prepared developer (red). Then you go from the middle of film 1 upwards to the straight line, then to the left, and can read off the appropriate development time: 3'15, i.e. 3 minutes and 15 seconds. Next, 2 films are developed simultaneously, which would be films 2 and 3 (green). Again, go from the middle of films 2 and 3 upwards to the line, then to the left, and you can read off the appropriate development time: 3'25, i.e. 3 minutes 25 seconds. Next, there are 4 films to be developed at once. These would be films 4 to 7 (blue). Again, from the midpoint of films 4 to 7, go up to the line, then to the left, and the correct development time would now be: 3'46. Film no. 8, another single film, would be 4'03 (purple). And finally, quite boldly, two stragglers at the same time, which would take 4'13 to develop (orange). Why always read from the middle of the ‘film load’? Because the developer’s activity decreases slowly and linearly over the development time; the more films at once, the faster it happens. And the average development time of all films developed simultaneously comes closest to the correct time. By recording the data in a diagram like this, you also have a log of the number of films already developed. If you don’t quite trust the chart, you can always increase the time slightly for your first attempts; for example, in the case of 4 films at once (blue), increase it to 3’50. After all, negatives with a slight increase in density are less of a problem than those with too little light. How accurately the chart applies also depends on the age of the prepared solution. Incidentally, the C-TEC 41 data sheet contains an error on page 4: for colour negatives, there is no pre-developer, only a colour developing agent. A pre-developer (a black-and-white developer) is only used for reversal films. Have fun! Wolfgang [attachment=3476]

Wolfgg

Of course, you could make things easier for yourself and assume that the developer remains completely unchanged in its properties throughout the development process, no matter how many films are being processed at the same time, and only ages suddenly right at the end when it’s poured back into the bottle. It’s a rather unchemical assumption, but anything goes. It just depends on what level of density tolerance you’re prepared to put up with. It would be a bit of a shame, though, for such a brilliant, precise little developing machine that has time, movement and temperature under control in a highly reproducible way. But perhaps the person who asked the question will test out what’s actually correct. Addendum: This was a response to the objection—which has unfortunately disappeared again—from a Dukakollegen from the English-speaking world. He argued that the number of films developed simultaneously is irrelevant to the development time; it only depends on the number already developed.