What is the performance criterion for darkroom fog testing?

• A. Less than 0.01 increase in density in 2 minutes
• B. Less than 0.10 increase in density in 2 minutes
• C. No change in density over 5 minutes
• D. Less than .05 increase in density in 2 minutes

Answer: (D)

Darkroom fog testing checks that safelight exposure doesn’t add unwanted density to film during processing. The standard performance criterion is that the density increase on a processed, unexposed film should be less than 0.05 optical density units within a 2-minute safelight exposure. This small tolerance keeps fog from masking or degrading diagnostic details while reflecting typical processing times and safelight conditions. A larger allowable increase, like 0.10, would risk noticeable fog; requiring no change over 5 minutes would be unrealistic for standard safelight testing, and a rate as strict as 0.01 might be impractical in many labs.