Sensitometry is the science of measuring the sensitivity and providing the photographer with an
objective testing and (select one)
quality control system.
THE FOUR PROCESSING VARIABLES AND THE DEGREE OF DIFFICULTY TO
The photographic process for quality work must be accurately controlled and repeatable. There
are four variables that must be dealt with in order to control the process.
(1) TIME -- In machine-processing, the time is based on the speed of the machine, which is
controlled electronically. If the machine speed is properly monitored and maintained, the variability of
time will be insignificant.
(2) TEMPERATURE -- Like time, temperature is controlled within the machine and must be
properly monitored and maintained.
(3) AGITATION -- In automatic machine processing the film is agitated by its continuous
movement through the chemicals.
(4) SOLUTION STRENGTH -- The variables that you will be most concerned with and that
MUST be monitored continually. The strength of the developer (or solution strength) is controlled
primarily by replenishment. This makes it the most difficult of the four variables to control.