1 The Director of Photography – an overview

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Three-point image
control
There’s no such thing as exposure latitude
Many photographers refer to a particular film stock as having plenty
of latitude; indeed, stock manufacturers often sell certain stocks as
having great, or extended, latitude. If we are to produce the very finest
images, it is important to abandon all thoughts of film having latitude
and use all the tonal range of the film.
If you are using a film stock with the ability to record an image with
a tonal range covering seven stops (that is, a lighting ratio of 128:1),
and you knew that the image was only ever going out on television,
which can only transmit a lighting ratio of 32:1, or five stops of tonal
range, then you could say that you had two stops’ latitude, one stop
above correct exposure and one stop below perfect exposure. But why
not go for a more appropriate exposure every time?
Even when shooting for television you might not want to put the
five-stop range in the middle of the sensitometric curve. If you were
shooting a night exterior you might wish to lay your exposure right on
the bottom five stops of the full exposure range, thus taking advantage
of the curved response at the bottom end on the sensitometric curve.
This would be very sensible, as the non-linear response to extreme
shadow detail at this point in the film’s sensitivity is very akin to the
human eye/brain response and can therefore, in these circumstances,
look both appealing and appropriate.
The same is true of a scene containing mainly highlights, say a snowscape.
Here you may decide to peg all your important tones right at the
top of the sensitometric curve, thus compressing the extreme whites as
they will sit on the non-linear part of the curve, where all the bright
whites start to go to absolute white. This can have the effect of appearing
to extend the information-recording ability of the film well into the
shadows, where you may wish to show more information.
If you are shooting with a film having a seven-stop overall range and
you are going to show the resultant picture in the cinema, where, as we
have seen, a really good projector/screen set-up can show the full
seven-stop range, then clearly you have no latitude whatsoever.
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