Contrast control

The individual tones within the subject can be moved closer together (lowering the contrast) by reducing the processing time, or moved further apart (increasing the contrast) by increasing the processing time. Decreasing the processing time decreases the density of the highlights on the negative whilst leaving the shadow tones relatively unaffected. Increasing the processing time increases the density of the highlight tones on the negative whilst leaving the shadow tones relatively unaffected. There is some effect on the mid-tones in both instances but proportionally less than the highlights. If shadows are missing from the negative (areas of clear film base within the frame) then no amount of extra development will reveal detail in these areas.

Negative with good detail Contrast exceeding the latitude of the film

Subject brightness range

The photographer can measure the contrast of the subject (subject brightness range) and then alter the processing of the negatives according to the desired contrast. The photographer exercises precise control by measuring the distance in stops between a highlight tone and shadow tone. If the distance between the selected highlight and shadow tones is greater than four stops (extreme contrast) processing can be decreased to lower the contrast of the image. If the distance between the selected highlight and shadow tones is less than four stops the processing can be increased to increase the contrast of the image.

Summary so far

~ The zone system is made up of ten major tones from black to white.

~ Each tone is one stop darker or lighter than the next.

~ Specific highlight and shadow tones of the subject are assigned to specific zones.

~ Zone placement of a shadow tone is a subjective decision. The decision dictates what detail is visible and how dark these shadows appear in the final image. Development affects highlight tones proportionally more than shadow tones.

~ Increased or decreased processing time leads to increased or decreased contrast.

~ Subject contrast is measured in stops.

~ Shadow tones are controlled by exposure and highlight tones by development.