Film & darkroom
Read a film characteristic curve before diagnosing exposure
The curve connects exposure to negative density and shows where tones compress.
When an old photobooth negative looks flat or loses face detail, a characteristic curve gives a more useful model than calling it simply overexposed or underexposed.
Find the axes
A sensitometric curve plots density against logarithmic exposure. Its toe, middle region and shoulder describe different response ranges. The middle region’s slope is contrast; it is not the same thing as film speed. Kodak’s teaching workbook illustrates how the three colour records can have separate curves.
Evidence: Manufacturer technical workbook
Relate the curve to a face
A face may contain both shaded and brightly lit areas. If those values fall into the toe or shoulder, small changes in scene brightness may produce little visible separation in the negative. Inspect several tones, including a neutral background, rather than judging only the darkest or brightest patch.
Keep the limits visible
A manufacturer’s curve is measured under stated conditions, not a promise for every camera, light source, batch or developer. Compare like-for-like samples and preserve the film and processing data. If the source conditions are unknown, describe the observed tonal loss without assigning a single cause.
Evidence: Manufacturer technical workbook
Sources & further reading
Sources for the specific facts and product descriptions above. Our worked examples, interpretations and practical suggestions are original editorial guidance.
- Eastman Kodak, Basic Photographic Sensitometry WorkbookManufacturer technical workbook