Chapter 3 The Video Camera and Support Equipment
63
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levels coming into the camera and opens or closes the iris according to the
generic defi nition of a “good” picture. The auto-iris is a useful feature for
most circumstances in television production.
The aperture is the opening, adjusted by the iris, through which light
passes. Aperture is nothing that can be touched; it is a hole.
Many cameras offer a manual iris control in addition to the auto-
matic circuit. Adjusting the iris manually is accomplished by moving the
f-stop ring. The f-stop setting determines the amount of light that passes
through the lens by controlling the size of the iris. If the camera lens has a
manual f-stop ring (some consumer cameras do not), numeric values are
written on the corresponding movable ring, Figure 3-18. When the f-stop
ring is manually turned, the operator hears or feels a series of clicks or
bumps that indicate movement from one f-stop to another. Lower f-stop
settings (numbers) allow a greater amount of light to pass through the
lens. Higher f-stop numbers indicate that smaller amounts of light can
pass through. The appropriate f-stop setting varies per situation, based
on the lighting in the environment and the brightness of the object(s) in
the shot. A lens that is capable of producing a large aperture and lets a
great deal of light into the camera is considered a fast lens. A lens that is
capable of producing a small aperture, allowing little light into the cam-
era, is considered a slow lens.
When shooting in high contrast situations, the auto-iris essentially
becomes confused. It fi rst adjusts to produce a good picture of the darker
items, but the lighter colored items then begin to glow. When automatically
adjusting for the lighter colored objects in the frame, the dark items lose all
fast lens: A camera lens that
can produce a large aperture
and let a great deal of light
into the camera.
slow lens: A lens that
produces a small aperture
and lets little light into the
camera.
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F-stop
numbers
Figure 3-18. The f-stop
ring is labeled with a
series of numbers.
aperture: The opening,
adjusted by the iris, through
which light passes into the
lens.
f-stop: A lens setting that
determines the amount of
light passing through the lens
by controlling the size of the
iris.