1 The Director of Photography – an overview

112 Practical Cinematography
If we are to work at these extremes, or even if we wish to be certain
that we are placing our chosen tones right in the middle of the
straight-line section of the curve, then we will need a simple and accurate
method of measuring the brightnesses in the scene and relating
them to the chosen film’s recording ability.
Three-point image control
To work to the accuracy required above you cannot use an incident light
meter. An incident meter can make no allowance for the reflectivity of
the subject behind it and that reflectivity can vary over huge margins.
A reflected light meter is required and one where the user is certain
of the exact area over which the reading is being taken. Such a thing is
called a spot meter. You will find a full description of a spot meter in
Chapter 10.
There is a very simple way of using a spot meter to very quickly give
you all the information you need for the most accurate positioning of
the tones of your scene on the sensitometric curve of the film you are
using. After a little experience you will not even have to think about
the sensitometry at all.
Point 1
In order to establish the correct aperture to set on the lens, take a
reading on the most important subject in the scene.As this will usually
be your main character in the scene, then use their lit skin tone. If they
are a Caucasian then the reading on your spot meter will be one stop
over the setting for an 18 per cent grey card.
As we have seen, the meter expects to be pointed at something having
a reflectance value of 18 per cent and Caucasian skin usually has a
reflectance of around 36 per cent. This means that if the skin reads
T5.6 then the lens should be set to T4.You can check this by substituting
the person with an 18 per cent grey card; this will read T4. In fact,
using the card is a very good way of setting this point when the person
is not available. Remember, the card must be placed in the exact position
of the face and should be set so that all the light that will fall on
the bright side of the face falls on the card.
The only other caveat is that all the readings for this technique must
be taken from in front of or very near to the lens, for only then will the
reflectance of all the surfaces in the scene be the same for the spot
meter as for the film.
Point 2
The second most important part of most scenes to most cinematographers
is the shadows, so measuring these becomes Point 2 of the
technique. We know that for cinema our tonal range goes around four
stops below camera aperture; therefore, without changing any of the
settings on your spot meter, look into the shadows in your scene. Four
stops below the exposure we have chosen, T4, is T0.9 – therefore, any
shadows that read above T0.9 will just have detail in them when shown
on the cinema screen and any that read below this figure will come out
as solid black.