Page 18 - Clinical Manual of Small Animal Endosurgery

6 Clinical Manual of Small Animal Endosurgery

Fig. 1.6 CCU with camera head plugged in. Photograph courtesy of Mr P.J.
Lhermette.

The camera head is connected to the endoscope via an adaptor,
which focuses and magnifies the image between five and 15 times. Diffe-
rent adaptors have different focal lengths, and zoom lenses are also
available.
The camera head can use one or three chips (or camera-coupling
devices, or CCD) to convert the optical (analogue) image into an elec-
tronic (digital) signal, which is then transmitted to the CCU. Although
single-chip cameras have lower horizontal resolution and less accurate
colour reproduction than three-chip cameras, they produce images that
are adequate for many procedures, and are more widely used. Three-chip
cameras use a prism to separate light into the three primary colours (red,
green and blue), and use a separate camera-coupling device to transmit
each of them. In this way colours are more accurate, and images obtained
are of higher quality, as all the signal available for resolution is used only
for that purpose. However the cost of these cameras is higher and they
are less commonly used.
Recently, high-definition cameras have become available, providing
five times the resolution of standard cameras. Some of these high-
definition cameras also provide images in widescreen format, which more
resemble three-dimensional images on the video monitor.
The CCU decodes the information and distributes it to the monitor
and other video devices, and also houses other features such as white
balancing and automatic exposure control. The former allows the camera
to compensate for variations in the colour of light, thus reproducing
colours accurately. With the latter, an automatic iris measures the avail-
able light and selects the shutter speed that will provide the best expo-
sure. In fact, bright reflections from white and/or shiny surfaces may
otherwise create the white-out phenomenon, causing light-coloured
objects to appear white as well and to lack detail.