Darkroom test strip (f-stop timing)
Even steps in seconds are uneven in exposure. Print in f-stops instead: pick a base time and a step size, and get a proper geometric test-strip sequence.
Give each strip the whole exposure time (cover the paper progressively, or expose separate strips). Read the print dry — highlights lighten as it dries.
About this tool
Even test strips should step in stops, not equal seconds, because the eye reads exposure logarithmically. Enter your base exposure, the step size in stops and how many strips you want. The calculator returns a geometric sequence of exposure times in seconds, so each strip differs from the last by the same visible amount.
How to use it
- Enter the base exposure time in seconds for your first strip.
- Enter the step size in stops, such as half or a third of a stop, and the number of strips.
- Read the exposure sequence in seconds and expose each strip to its time.
FAQ
Why use f-stop steps instead of equal seconds?
Equal seconds bunch up the highlights and stretch the shadows unevenly. Stepping in stops doubles or halves the light in even perceptual increments, so the difference between neighbouring strips looks consistent across the whole strip.
How do I expose the strips in practice?
Either cut separate strips for each time, or cover the paper progressively so each band accumulates to the next value in the sequence. The listed times are total exposures for each strip, not the extra time to add.