PHOTOGRAPHY 73
are fundamentally the same except that, rather than
exposing film to light, a light-sensitive chip converts light
into an electronic signal. This allows the image to be stored
digitally on a computer.
Both film and digital cameras have built-in light
meters, which measure the amount of light in the frame.
This allows for the manual or automatic setting of aper-
ture and shutter-speed, depending on the type of camera
system being used.
The depth of field is the range over which the image
appears in focus. This can be increased by reducing the
size of the aperture (smaller hole) with a higher numbered
f-stop, say from f4 to f11. There is, however, a trade-off.
For example, in an underwater or low-light situation, in
order to get a reasonable depth of field, a small aperture
is used which, for a correct exposure, requires a slow shut-
ter speed. To avoid camera-shake, a faster film or more
sensitive ISO setting must be used, which in turn reduces
image-quality. The alternatives are to use a tripod and/
or flash, as well as changing the focal length of the lens
(i.e. changing to a wider-angled lens).
Most compact digital cameras have a macro setting,
usually indicated by a flower icon. Traditional cameras
do not have such a setting and when it comes to non-
digital cameras, only SLRs (single-lens reflex cameras), with
a macro lens, can be used for close-up photography – for
example, artefact photography (see below).
Digital Photography
Traditional photography has changed dramatically with
the introduction of digital cameras, which offer, amongst
other things, excellent image quality. There are sim-
ilarities between film and digital cameras in that they
both have lenses with apertures, viewfinders, shutter
releases, shutter speeds, light meters, focusing mech-
anisms and a method of storing the image (i.e. film or
memory cards).
Inside the digital camera, behind the lens, there is a light-
sensitive electronic chip that converts light energy into elec-
trical impulses. The electrical impulses are processed into
an image by an image processor and saved on a memory
card. The quality of the saved image is based on the
number of pixels that make up the chip, and on the
quality of the lens and the image processor.
Most digital cameras have a few useful extras like a
liquid crystal display (LCD) screen. The instant feedback
offered by the LCD screen enables better control of com-
position, exposure and lighting because images can be
reviewed, camera settings changed and the images re-shot.
The size of the LCD screen is important – larger screens
are better for reviewing photographs, especially when
under water.
Another feature of digital cameras is the control of ‘white
balance’, which corrects colour for differing lighting
conditions. This controls the camera’s interpretation of
the colour of light by correcting the image to make
nearly any light look neutral. The camera defaults to
automatic white balance (AWB), although there are pre-
sets for specific light conditions like sunrise and sunset.
Video cameras also have similar white balance con-
trols. The resolution of a digital image is defined as the
number of pixels it contains. A 5-megapixel image is
typically 2560 pixels wide and 1920 pixels high and has
a resolution of 4,915,200 pixels (rounded off to 5 million
pixels).
With digital photography, there are three main variables
that can be altered by the photographer: the image size,
quality/resolution and file size. Altering any one of these
variables will have an affect on the other two. When
deciding what settings to use, it should be remembered
that the end result needs to be fit for purpose. For
example, an artefact record photograph for the database
can have a small image size and low resolution but for
publication, the resolution will need to be high and the
image size large (see chapter 8).
Most camera images can be saved in three formats:
JPEG (Joint Photographic Experts Group), TIFF (Tagged
Image File Format) and RAW. For most compact cameras,
JPEG is the most popular digital image format, allowing
images to be compressed by a factor of 10 to 20 with
very little visible loss in image quality. In most cameras,
images can be saved at three compression ratios. The
degree of compression has a significant effect on the
image quality/resolution and file size (a lower rate of
compression results in a larger file size). Digital SLRs have
two further formats: TIFF and RAW. Unlike JPEGs, the
TIFF option supports 16 bits/channel multilayer CMYK
(cyan, magenta, yellow and black – the primary colours
in printing) images and compresses files with no loss of
information, and it is therefore the preferred format for
printing and publishing. RAW, as the name implies,
refers to the raw unprocessed data. It gives very high image
quality, and is the starting point for all other formats. A
RAW image retains all of the image data available to the
sensor that recorded it, allowing maximum manipulation
of the image without degradation. The downside is that
it needs further processing and the file sizes are large.
Remember that a small image can always be created from
a large file, but a large image cannot be obtained from a
small file.
The master-list of photographs should be the best that
can be afforded, including the price of storage (CDs or
DVDs or an external hard drive). From these originals,
all future copies can be made.
A drawback with most digital cameras, except digital
SLRs, is that they suffer from shutter lag. This is the