3.
CAMERA STYLES AND SELECTION. Historically, video cameras have been
mounted outside of the pressure chamber looking through viewports. Cameras
have also been designed to be installed within pressure housings and placed
within the chamber compartments. These cameras have not been successful
because of helium leakage into the videocon. The exception to this is when
the camera is placed underwater. Because video cameras are normally
observing a single spot, an image can burn in the videocon. After the image
is burned into the videocon, the actual occurrences are masked and the
occupants cannot be observed. To prevent this burn, a camera equipped with a
silicon diode videocon is the only approved type for use in chamber
operations.
4.
CAMERA LOCATIONS. The prime location for externally mounted cameras is
through viewports. Caution should be taken not to face cameras directly into
a chamber light or a highly reflected light. The viewport selected for the
camera for best overall chamber observation should be high and unobstructed
by chamber appurtenance such as bunks or shower curtains. If a new chamber
is being designed, a camera port as shown in Figure 10-3 should be
considered, located at the end, high and at a 45 deg. angle from the deck
plates. This will provide the overall best image of the entire chamber.
5.
LENS SELECTION AND FIELD OF VIEW. The need for auxiliary lenses on TV
cameras, whether internally or externally mounted, will be governed partially
by the chamber geometry. A long, narrow chamber is more difficult to cover
with a single lens and may require more than one camera as well. Lenses with
effective focal lengths which are equal to or smaller than the image tube
breadth can cover a wide area with small magnification and are called normal
lenses. Lenses with effective focal lengths considerably greater than the
image tube diameter cover a small field with high magnification, that is, a
telescopic effect, and are called telephoto lenses. Extreme wide-angle
coverage can be obtained by use of special lenses, but usually with
noticeable
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