80 PHOTOGRAPHY
and if appropriate a copyright statement can be added
at the end.
This section concentrates on the use of camcorders.
However, for more commercial underwater use, there
is also a system using a small video camera sealed in a
housing with a hardwire umbilical to the surface where
the control unit and video recorder is located. These are
mainly used on surface-supplied divers’ helmets and on
underwater vehicles, like ROVs. Their advantage is that
they are powered and controlled from the surface, via
an umbilical, so there is no problem of battery power
for the camera and lights. ROVs usually carry an addi-
tional low-light black-and-white silicone intensified (SIT)
video camera to give an overview and use the colour
camera for detail.
For underwater use, a camcorder in a housing is ideal
for archaeology, where the diver controls the camera.
The disadvantage is the restrictions imposed by the lim-
ited battery life, especially when it comes to powering the
underwater lights. The camera itself uses lithium-ion
batteries that last up to 5 hours or more. Traditional
underwater lights, however, have a low burn-time of less
than an hour. The latest xenon high-intensity discharge
(HID) lights (for example, Treble Lights) produce high-
intensity white light, daylight balanced (colour tempera-
ture of 5600K), which burns six times brighter than
a standard halogen bulb. These lights can be fitted with
low-wattage bulbs, resulting in excellent burn times,
but they are expensive. It should also be noted that
rechargeable batteries lose their capacity with age as
well as in cold water.
There are numerous different types of camcorders.
Apart from the quality of the components, the main
differences relate to the format, which affects the image
resolution and quality. The basic functions are usually
fully automated, like auto-iris for correct exposure, auto-
focus, auto-white balance (to ensure correct colour
reproduction) and auto-audio levels. Most of these func-
tions have manual overrides. Like a digital still camera,
the image from the lens is focused onto a single charge-
coupled device (CCD) chip. More professional camcorders
have three CCDs (referred to as three-chip cameras) and
consequently produce a better quality image.
The most popular digital tape format is MiniDV. One
of the main criteria is resolution: normal VHS is
200 –250 lines, Hi-8 and Super VHS (SVHS) is 350 – 400
lines and MiniDV is 400 – 480 lines. Some three-chip cam-
corders have a semi-pro version using a format called
DVCAM (500 – 650 lines), which can be recorded onto
MiniDV tapes. The latest development is HDV (1080 lines),
which is a new video format that records high-definition
pictures onto either a standard MiniDV tape or an HDV
MiniDV tape. The hierarchy progresses from single-chip
to three-chip MiniDV to DVCAM to HDV. Sony’s latest
Pro-HDV camcorder is switchable and can record and
playback in MiniDV, DVCAM or HDV formats. It can
also record and playback in PAL (phase alternating line,
the colour television coding system used for European
broadcasting) and NTSC (National Television System
Committee, the American colour TV broadcasting system).
Digital tapes can be copied without loss of quality and
similarly they can be captured on a computer through a
digital ‘firewire’ (IEEE 1394) connection. These can be
edited and then exported back to digital tape without any
loss of quality. Alternatively, a DVD can be made of the
final edited movie, which will play on a domestic DVD
player as well as on a computer.Video Technique
Camcorders are able to operate in low light. Under water,
they often ‘see’ better than the diver. However, the same
problems that occur with underwater photography occur
with video – poor visibility, loss of light, colour and con-
trast. To reduce these problems, the use of a wide-angle
lens is advisable. This shortens the camera-to-subject
distance and maintains a large depth of field. It is also best
to shoot within one-third of the visibility and to use
artificial light. However, if the light is held too close to
the camera it may cause the problem of backscatter. It is
best to shoot around the middle of the day when natural
light levels are at their best.
On the surface, professionals use manual focus,
refocusing for each shot. They zoom into the subject,Figure 10.9 Underwater use of a video camera (Photo:
Kester Keighley).