Image Processing Reference
In-Depth Information
Fig 5.3 a lens adapter (Nikon
lens/Canon camera).
One technique that the manual lens allows the cinematographer to
practice is the “rack focus.” This is a classic live-action effect that allows
the filmmaker to direct the eye of the viewer from one object or person to
another object or person when they are separated by depth in the frame.
A foreground element can be in sharp focus and a background element in
soft focus. The story suddenly requires the background element to be seen
so the camera lens can be shifted to move the focus and attention from
the front to the back of the compositional frame. This is usually executed
by using gentle ease-in and accelerated turns of the focus ring on the lens
including an ease-out over a short number of frames (i.e., 10 to 20 frames).
The move can be done by hand with a measuring device on the lens (like
a piece of tape with marked increments) or achieved through a motion
control setup.
Depth of field is an important element to consider when shooting with a
dslr camera. The basic principle is that the lower the number on the f-stop
(e.g., f-1.4, f-2.8), the more narrow the depth of field or range of the focus.
The audience automatically looks at focused objects in a composition,
because people seek information that they can understand. That is why
the rack focus or shifting focus is so effective in directing the viewer. The
narrow focus also allows the focused object in the frame to stand out in
contrast to its soft-focused surroundings. If you have a relatively busy
background over which you have no control, then you might consider
opening up the iris to create a shallow depth of field to help your subject
stand out from the background. The danger with this is that, if your
subject is moving in the “z axis” or toward and away from the camera, then
that subject may fall out of focus in the action. It is also worth noting that
every lens has a different range of focus. The wider the lens is, like 14 mm
to 35 mm, the deeper the range of focus or depth of field. Longer lens
and macro (or close-up) lenses have a much narrower depth of field. So,
a 24 mm lens at f-8 has a broader depth of field than a 85 mm lens at f-8.
Using this knowledge can increase your sense of composition, narrative,
and atmospheric quality and is one more tool to give your film a sense of
style and purpose. If you view any of the films of the Brothers Quay, like
the 1986 Street of Crocodiles , you will see a mastery of this use of depth
of field.
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