Speed Calculator

How to choose the speed on your linear processor

Film stocks all have different responsiveness to the developing process, and different chemistries have different strengths. Temperature and film age also affect the time that your film should stay in the developer. There are a few guides and data collections out there that can help you choose your speed based on these factors, but what if you can't find your film in the list?

Much like with the stills printing process, you can incrementally develop a strip of test film of the same stock to determine how long the film should stay in the chems.

1. Fill your processor, and wait for the chems to reach the target temperature if you have installed the heat system.
2. Prepare a 6 to 12 inch strip of film the same stock as the one you want to develop.
3. Ready a stopwatch, such as one in a phone app
4. Submerge as much of your test strip as you can in the developer stage, but don't let go!
5. Wait ten seconds, then pull out about a half-inch of film.
6. Repeat the previous step, pulling out another half-inch every ten seconds. Rest your hand on the edge of the tank between steps to keep the film still between increments
7. Once you have pulled out all of the film, observe the stepped gradient from clear to dark.
8. Count how many steps it takes for the film to stop getting darker. Multiply this number by ten seconds (or however long you waited between pulls) to get the time that the film should get in the developer.
9. Use this time in the calculator below to get the speed percentage to set the motor to.
10. If the number is above 100%, you may need a faster motor. You can also lower the temperature or fill the developer tank to a lower height.