Calibration tests

The following additional tests can be conducted to check the accuracy of exposure and processing time.

Note > Changing printing papers or type of enlarger (diffusion or condenser) will change the tonal range and contrast that can be expected and so therefore should be avoided.

Exposure

The exposure index is calibrated by checking the accuracy of shadow tones on the negative. This can be achieved by using a ‘densitometer’ or by conducting the following clip test.

~ Underexpose a gray card by three stops (Zone II). ~ Leave the adjacent frame unexposed. ~ Process the negatives according to the manufacturer’s specifications. ~ Place half of each frame (unexposed and Zone II) in a negative carrier.

~ Make a step test using a normal contrast filter or grade two paper. ~ Establish the minimum time to achieve maximum black (MTMB). ~ The tone alongside the MTMB should appear as Zone II (nearly black).

MTMB Zone II

If the adjacent tone to the MTMB exposure on the test strip is too light (dark gray), decrease the exposure of the film. If the adjacent tone to the MTMB exposure on the test strip is too dark (black), increase the processing time.

Processing is calibrated by checking the accuracy of the highlight tones on the negative. This can be achieved by using a ‘densitometer’ or by conducting the following clip test. ~ Overexpose a gray card by three stops (Zone VIII). ~ Leave the adjacent frame unexposed. ~ Process the negatives according to the manufacturer’s specifications. ~ Place half of each frame (unexposed and Zone VIII) in a negative carrier.

~ Make a step test using a normal contrast filter or grade two paper. ~ Establish the minimum time to achieve maximum black (MTMB). ~ The tone alongside the MTMB should appear as Zone VIII (light tone).

If the adjacent tone to the MTMB exposure on the test strip is too light (paper white), decrease the processing time of the film. If the adjacent tone to the MTMB exposure on the test strip is too dark (Zone VII), increase the processing time.

MTMB Zone VIII

Activity 4

Choose a 100 and 400 ISO film and conduct the exposure and processing tests as outlined on these pages. Discuss your findings with other students.