C-41 timing technique

Discussion in 'Film and Processing' started by craig_shearman|1, Dec 21, 2012.

  1. When developing B&W I have always started the timer as I begin to pour the chemicals into the film tank. So I'm about 10 seconds into the developing time by the time the tank is full of developer. I begin pouring out about 10 seconds before the time is up so the tank is empty when the time is up. (my tank takes about 10 seconds to fill and 10 seconds to dump)

    I'm getting ready to do C-41 and I'm concerned because the timing (and temp) is much more critical. The recommended time is around three and a half minutes.

    So, my question is -- should I 1) start the timer as I begin to pour developer into the tank and start dumping about 10 seconds before the end the same as I do with B&W, or 2) start the timer once the tank is full and start dumping once the full 3.5 minutes is up?
  2. Back when custom labs were abundant the lab would push or pull color film 10% to compensate for exposure variance without extra charge. The labs also required film to be exposed at twice its box speed as they did not need the extra density to make good prints.
    3:30 processing time at 102°F, 10% of that time is 21 seconds. 10 second fill/dump time is 5%.
    If your film is slightly underexposed or dimly lit subjects start timing at the end of pour in, slightly over exposed or brightly lit subjects start timing at start of pour in. Being consistent and keeping chemical temperatures correct is the most important.
  3. The nominal developer time is 3 minutes 15 seconds. If a processing error of +40 seconds occurs, the gain in density is +0.10 units of density. That amount is equal to 1/3 f/stop.
    + 0.20 units of density = 2/3 f/stop.
    +0.30 units of density = 1 f/stop.
    In other worlds, adhering exactly to the time specification of the developer is not as critical as you think. Reference Kodak C-41 manual Z-131 section chart 2 page 5-30.
    The other chemical steps are not super critical.
    As a rule of thumb, timing starts at the beginning of the pour and ends at the beginning of the next chemical step pour.
  4. I pour, set the stop watch and dump at 3:10. Probably 3 1/2 minutes total in developer. Have had no problems. As Alan points out a few seconds here or there seem to make little difference. BTW I shoot a 200 film at 100 using standard times. Again films look great.

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