One of my most popular posts, according to my WordPress stats, was one I wrote in 2015 which reprinted a legible version of the instructions for the Fuji Hunt X-press C41 developing kit.
A few readers have asked for more explanation of one table in the instructions – this one below:
So I’ll try to put in into words and see if I can make it clear. First, I’ve actually amended the title of the last column to make it clear that this table would apply if you made up all of the chemicals it once, to give you 5 litres of solution. Unless you’re processing film commercially, or you shoot an awful lot of C41 film in a short space of time, this might be unlikely and the instructions will have to be amended for a smaller amount of chemicals. But I’ll come to that a bit later …
So we’ll start off by just looking at the first data row in the table, which applies if you are developing ISO100 film in 120 format. The last column tells us that the most films which Fuji think you can develop with 5 litres, is 120 films.
- When you develop the first 16 films with this 5 litre batch of chemicals, you would use the processing time 3’15” (3 minutes and 15 seconds).
- When you develop the NEXT 16 films with the same 5 litre batch of chemicals, then you increase the processing time to compensate for the partial exhaustion of the chemicals. The new processing time is 3’18”
- When you develop the NEXT 16 films you increase the development time to 3’23”
- When you develop the NEXT 16 films you increase the development time to 3’26”
- When you develop the LAST batch of 16 films you increase the development time to 3’27”
At this point, Fuji recommends that you should not develop any more films with this batch of chemicals.
However, there are a few problems with this explanation:
- The mathematically sharp-eyed amongst you will have notice that 5*16 is 80, not 120. So either the maximum number of films that can be developed with a 5 litre batch is 80, rather than 120, or you should increase the batch size before increasing the development time, to 24 instead of 16. There are a few other threads on the web which suggest that this aspect of the Fuji instructions don’t make sense, so it’s hard to have confidence in the calculations.
- If you have the type of processor that allows you to program the development time exactly, then you can easily increase the development time by 3″ … but if you are filling and emptying the tank by hand then can you really be that accurate ?
- As I said above, most amateur users are going to want to mix smaller quantities because unmixed chemicals last longer than mixed chemicals. If you mix 5 litres in one go then there is a higher risk that the chemicals go “off” before you have developed the maximum theoretical amount of films than if you mix a smaller amount.
- Depending upon the make and model of your development tank, then the number of films you process at once might not be a divisor of 16, or 24. For example if you develop three films at a time then you would need to change the development time after 15 films instead of 16.
- In reality the degree of exhaustion of the chemicals will change gradually with each processing cycle rather than in a jump-step every 16 films, so the table can never be more than a guide.
So what do I do in the face of this confusion ? I operate a much simpler system.
I choose to mix 500ml of the chemicals at a time, and usually develop between 6 and 8 films using that 500ml batch, with a development time of 3’15”. This applies regardless of whether the films are 120, 35mm * 24, or 35mm * 36 exposures. The C41 films I use are rated between ISO100 and 400 and I don’t distinguish between them. I don’t use any faster C41 films.
There is nothing very scientific about whether I mix new chemicals after six films or eight; if I have developed 6 films but it was some time since the batch was first mixed then I will probably mix a new batch, but if I have 8 films ready to develop in a short space of time, then I could do eight from one batch.
500ml of chemicals might not be the right amount for you because this depends upon the processing tank you use, and also whether you are using agitation or rotary processing.
Since I can mix ten 500ml batch out of the 5 litre kit, then in theory I will develop somewhere between 60 and 80 films from the kit. This is the capacity I have seen advertised for the kit.
I say “in theory” because I don’t think I’ve every reached the theoretical capacity with any C41 kit, whether it be Fuji Hunt, Tetenal, or Rollei Digibase, because I have a bid habit of doing something clumsy like knocking over and spilling one of the components.
On the other hand, there are those on the web who talk about reaching much higher capacities than those advertised. That might well be possible, but for my uses I want to stop before image degradation becomes apparent.
When I started writing this post, I had hoped to clear up some confusion, but I realise I may have added more. Such is life.