"... you will find that much of what you may have read or heard about the characteristics of photosensitive materials is unreliable and misleading."
Sensitometry is the scientific study of the behavior of photosensitive materials, in relation to a given exposure and a given development.
This allows us to investigate the real characteristics of the materials we use, in the context of our work chain.
We will be able to obtain certain and repeatable data of fundamental importance, such as the real ISO sensitivity (actual speed of the film), slope of the Ğ (Average gradient or contrast of the negative), to be related to a specific treatment, development time, temperature, concentration , agitation etc ...
All these variables can be put under the close control of the photographer, who will have the ability to consciously position the areas (shades) of the subject where he wishes best.
Personally, I have always sought maximum control of the process in my photographs. This is in the obvious attempt to predict the final result as accurately as possible, so as to intervene and modify the many variables that lead to it.
The study of sensitometry has engaged me for more than three years, the last of which was an authentic “Full Immersion”, and its deepening is in continuous evolution.
A common criticism of Sensitometry is that to be applied it requires a considerable degree of technical precision, this, according to many, limits creative interpretation.
Personally I do not share this opinion at all, but on the contrary, I think that only by knowing exactly the behavior of the materials we use, we will be able to free a conscious and creative visualization!
I perform my tests using the following equipment and treatment methods.
Magnifier LPL 7451 Color head with diffused light
Heiland electronic TRD2 densitometer
VOLTCRAFT MS-200 LED Luxmeter
RS PRO RS1710 Digital Thermometer
Step Tablet Stouffer, 21 steps for roll films
Step Tablet Stouffer, 31 steps for 4x5 films
Tank AP for roll films
Tank Paterson and MOD 54 for 4x5 films
Exposure, type of development and dilution are specified case by case
Temperature 20 °, continuous stirring on 1 ', then 10 "every 1'
The films are developed for progressively longer times of about 40%, usually 4 ', 5'30 ", 8', 11 ', 16'.
"Producing a perfect image by means of photography is an art.
The production of a technically perfect negative is science. " Ferdinand Hurter
The data reported are those that I have extrapolated from the tests that I have personally carried out and that prove to be correct in MY chain of work.
In fact, there are many factors that can misalign the test results from one work chain to another.
Small differences in the reading of the exposure or in the calibration of the exposure meter, as well as in the many other devices that the process necessarily passes through, shutters and thermometers in the first place, not to mention all the possible deviations that can occur in the development process in the room obscure when not meticulously executed.
All these variables, if combined with each other, can lead to significant shifts in the results.
In any case, if the film is consciously exposed according to the dictates of the Zonal System, and the treatment parameters are respected and replicated (time / dilution / temperature / shaking etc ...), I believe that the data obtained can be a good starting point. from which to move, to adapt them to other work chains.