1 The Director of Photography – an overview

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Exposure meters
Exposure meters measure brightness. Some measure the light reflected
back from the scene and others measure the amount of light falling on
the scene.
This chapter considers the matters to be taken into account when
taking a reading and interpreting it on the meter’s scales.
Camera speed
In cinematography things are mostly simpler than with still photography.
You still have shutter speed and lens aperture, but your shutter
speed is nearly always the same, since it is primarily dictated by the
number of frames per second the camera is set to run at.
For the cinema the standard frame rate is 24 fps (frames per second)
and for television we shoot, in the United Kingdom, at 25 fps. Most
cameras use a 180° shutter – that is, the shutter is closed for exactly
half the time and open for the other half. Some cameras can vary this,
but we are not concerned with that facility at present, especially as it is
rarely used. For US television 24 fps is most common, but when exceptionally
high quality is required 30 fps may be used.
Shutter speed
If we are running the camera at 24 fps, which is the standard frame rate
used in the cinema, and the shutter is open for only half the time, what
will the exposure be? As each frame is replaced every twenty-fourth
of a second and the shutter is only open to the film for half that time,
then the exposure must be one forty-eighth of a second.
If we are shooting for UK television, then the same logic applies,
though the frame rate here is 25 fps and, therefore, each frame takes
one twenty-fifth of a second.The shutter is again open for only half the
time, so the exposure will be one fiftieth of a second.
In practice, we find that some exposure meters don’t have a fortyeighth
of a second setting but virtually all have a fiftieth, which is fine
for the television frame rate of 25 fps. For cinema, the difference is an
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