How the Development Advisor works

Summary

Calculator that takes the brightness range of the scene and a target Contrast Index and recommends whether to develop normally, push (N+), or pull (N-) to land at the contrast you want.

How it works

When you develop a black and white roll, you can lengthen or shorten development time to push or pull contrast. This advisor takes the brightness range of your scene and your target contrast and tells you whether to develop normally (N), give a bit more (N+1), or give less (N-1).

SBR (Subject Brightness Range)

How many stops of light separate the brightest and darkest important parts of the scene. A flat overcast portrait might be 4 stops. A sunlit street with deep shade might be 9 stops. Take a spot reading of the brightest highlight you want detail in and the darkest shadow you want detail in, and the difference is your SBR.

Target CI (Contrast Index)

How contrasty you want the final negative to be. Higher CI gives a punchier negative; lower CI gives a softer one that is easier to print. CI 0.56 is the classic Ansel Adams target for diffusion (condenser) enlargers; CI 0.42 to 0.50 is more typical for variable-contrast paper printing today.

Film latitude

Each emulsion has its own contrast curve. Pick your film here. Tabular-grain films like T-Max behave differently from traditional grain like Tri-X, so the advisor adjusts the recommendation.

The recommendation

If your scene SBR is short (a flat day), the advisor pushes development (N+1, N+2) to add contrast. If your scene SBR is long (harsh sun), it pulls development (N-1, N-2) to compress the range so highlights do not block up.

Rule of thumb

Each step (N+1, N+2 or N-1, N-2) typically corresponds to a 15 to 30 percent change in development time depending on the developer. Check your developer's data sheet for exact times.