What is the performance criterion for the darkroom fog test?

• A. Less than .01 increase in density in 2 minutes
• B. Less than .05 increase in density in 2 minutes
• C. Less than .1 increase in density in 5 minutes
• D. No change in density

Answer: (C)

The test checks safelight compatibility by measuring how much fog the safelight causes on unexposed film during a typical processing cycle. The performance criterion is that the increase in optical density from fog should be less than 0.1 when the film is exposed to the safelight for a 5-minute interval. If the density rises by more than 0.1, the safelight is contributing unacceptable fog and could degrade image quality. This 0.1 density limit over five minutes provides a practical threshold that accounts for typical processing, while acknowledging that some minor fog can occur but must stay under this level.