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applications include examination of

old faded documents under UV to

obtain better sharpness. Also,

different inks show a difference in

visible fluorescence when

illuminated with UV sources.

UV aerial photography of

snowy regions helps in the

identification and counting of

animals with white coat that

reflects all visible wavelengths.

While the snow also reflects

Figure 13.7 Image illustrating UV fluorescence of pollen. © Bjørn Rørslett/ strongly UV (which explains why it
NN/Samfoto. is so easy to get a sunburn while
skiing), an animal’s coat absorbs it.

Other applications where UV

imaging is important include

astronomy and remote sensing.

UV photography may be used less often than infrared for creative purposes but you can

certainly produce very pleasing imagery by employing UV techniques. In exterior scenes foliage

appears darkish due to low UV reflectance (unlike infrared), while water is very bright because

the surface reflects plenty of UV (this is why we also get sunburned when swimming). Flowers

emerge differently than in visible records because there are different amounts of UV reflected

from flower petals, often much less in the central area of the flower. Also, the nectar glands and

pollen may fluoresce under UV illumination (Figure 13.7). UV visible marks on the petals attract

bees – which have a UV-enhanced vision – towards the nectar and pollen of the flowers. This

makes UV imaging useful to natural scientists.

UV sources and filters
There are various UV sources with different compositions and methods of use. As with all types
of photography sunlight is the most available and cheapest source but the intensity of UV is very
variable. It contains long, short and some middle wavelengths of UV. Although much of its short
and middle UV content is lost on its way to the earth’s surface, much of the long passes through
the atmosphere, especially in bright sunny days. In contrast, common tungsten and tungsten–
halogen lamps which are rich in infrared are poor UV sources; the latter when operated in high
temperatures and contained within a quartz envelope emit some UV.

UV fluorescent tubes coated with a special phosphor (Wood’s Coating) absorb most
visible and transmit most UV with long wavelengths used in photography. The tubes appear
as a very deep violet-blue and they are referred to as ‘black lights’. They are the most available
UV sources. Another suitable artificial source is the electronic flash which can be used
efficiently in combination with aluminium reflectors. Be aware, as often flash units have UV-
absorbing glass over the flash tube for the purpose to reduce UV output. This must be removed
before the exposure. Otherwise high- and low-pressure discharge lamps emit some strong UV

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lines. Arcs provide substantial

emission of UV and are still used as

primary sources in photography. The

Blackout room xenon arc lamp is a pretty good
continuous source of UV.

As with infrared, you need to use

blocking filters to record only the UV

reflected from your subjects. These

UV-transmitting filters, such as the

Hoya U-360 or the Kodak Wratten

18A, are commonly known as ‘black

light filters’; they may have some

violet and infrared transmittance too.

In contrast, photographic UV-

absorbing filters with spectral

transmissions named as ‘UV’, ‘haze’,

‘skylight’ are related to Kodak

Wratten series such as 1A and 2B–2E.

These absorb UV radiation and reduce

the effects of haze without affecting

the rendering of visible colours.

Absorbing UV filters protect from

Visible light harmful UV and can be found in
Ultraviolet sunglasses, goggles and protection
Fluorescence sun lotions. In photography glass
filters are placed over the lens to avoid

much UV to fall on films and camera

UV source Light source UV barrier Visible barrier Lens sensors, to which they are naturally
sensitive. Use ‘barrier’ UV filters that
with UV content filter filter

Figure 13.8 For recording UV fluorescence use a UV barrier filter to stop UV almost totally block UV when you
entering the lens so that you can only record the fluorescence from the subject want to record only the fluorescence
(top). In UV reflectance use a visible barrier filter so that you can record only from subjects that occurs in the
the UV reflected from the subject (bottom). visible (Figure 13.8). For UV

fluorescence an exciter filter can be

placed over the source to allow only those wavelengths through which will cause fluorescence.

UV reflectance techniques
In UV reflectance photography the reflected UV from the subject is captured while visible is
blocked with UV exciters in front of the camera lens. All silver halide films, including colour
negative and slide films, are sensitive to near UV although pure UV images are recorded only in
the blue-sensitive layer. For striking, unusual imaging you can use false-colour infrared slide
with appropriate filtration to block the visible and capture simultaneously UV and infrared
reflected from the subject, with the UV recorded on the blue and the infrared on the

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red-sensitive layers. Images formed with UV tend to be low in contrast and therefore high-
contrast films or development should be preferred. Exposure times vary from 4 to 15 stops over
what is needed for capturing the visible. Photographing UV reflectance requires a lens that
passes sufficient amounts of radiation, thus less compensation is required when using quartz
lenses. In any case it is necessary to use a tripod and bracket exposures. Owing to long
exposures reciprocity law failure effects may be present.

Remember that UV focuses in a different point to visible, but the focus point displacement is
opposite to that of infrared. Unlike infrared photography, correction is not achieved by altering
the lens’s focal point as there are no UV markers on any SLR lenses. To achieve sharper results
focus on the subject in visible light and then close down the aperture to obtain more depth of
field. The shorter the focal length the less stopping down you need. Test exposures are the best
means for determining the optimum aperture.

Digital camera sensors without UV blocking filters respond to UV too, but are not used as
much as they are for infrared recording. Exposure compensation depends largely on your
sensor’s response and the lens’s UV transmittance. It also depends on the available levels of UV
radiation and the filter’s transmittance. When using non-SLR cameras real time viewing of the
picture on the LCD helps exposure – which can be handled usually quite well by the camera –
focusing and composition. One way to ensure correct exposure is to check the LCD histogram.
As in the case of infrared, RGB digital images are weirdly coloured, with some cameras yielding
bluish and some pink or magenta results. Contrast is also low. Since you might end up with
relatively long exposures digital noise is likely to degrade your pictures. Similarly to infrared,
post-manipulation is required to turn images to black and white or to ‘false-colour’ records. See
infrared photography above for colour manipulation techniques, noise removal and contrast
optimization.

UV fluorescence techniques
In UV fluorescence a visible record is obtained from subjects that glow when they are illuminated
with UV, whilst UV barrier filters block the UV from entering the lens. Fluorescent part of the
subject will glow brightly and you will record exactly what you see (without the barriers the subject
is recorded as if bathed with blue light, blotting out most colours). To photograph the fluorescence
excited by UV usual colour films and digital sensors can be used. To capture only the glowing
visible wavelengths you need to work on a blacked-out studio with your subject illuminated by one
or more UV lamps, which usually emit a dim blue light. For controlled fluorescence, use exciter
filters over the source. Indoors you might choose to add a little visible daylight from back, the side
or the rear. Otherwise the fluorescent parts of the subjects will bath in a black sea. Outdoors
natural light does this job, but you might want to filter out some reflected wavelengths, using
appropriate colour filtration, to allow mostly the coloured fluorescence to pass.

Apart from flowers, minerals are good subjects for creative photography as well as
especially designed plastic jewellery, day glow inks on posters and graphiti sprays (Figure 13.9).
Even washing liquid, face powder and teeth will glow to a greater or lesser extent. Some parts of
banknotes and labels for consumer products will also fluoresce when illuminated with UV.
Measure exposure from the fluorescing parts using regular techniques with your camera or light
meter. Spot measuring is often best. Be always aware of the danger of the UV lamps, so use
UV-absorbing goggles.

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Figure 13.9 You can use several products for creative photography using UV lighting.

Underwater photography

Most underwater photography is intended to show fish and plant life. However, you
may also want to take underwater pictures of products, ranging from industrial
equipment to fashion items (Figure 13.10). Yet another facet is record photography
of wrecks, archaeological objects or marine engineering subjects.

You can photograph

small objects, fish and plants

in a glass-sided aquarium.

True underwater

photography, however,

means shooting with your

equipment submerged. Apart

from having waterproof

equipment you have to also

be aware of the changes

created while imaging in the

water and not in the air, as

refraction of the light rays in

water is greater than

Figure 13.10 An impressive angle on the butterfly stroke, showing how an Olympic refraction in the air (see
swimmer expels air underwater. Chris Smith took this sport shot sitting at the bottom of Langford’s Basic
the pool using a 35 mm lens on a conventional SLR camera. Photography). As a result,

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underwater subjects appear closer and larger than they actually are. This upsets distance guessing
and focusing, but otherwise the camera is affected the same ways as your eyes. Never underestimate
the potential dangers of diving underwater and try to always have one other person with you.

Photographic equipment and techniques

Water causes serious spectral absorptions. As a result, daylight reduces in intensity and changes

colour content (loosing red) with increased depths. Beyond approximately 10 m depth there is no

colour differentiation and natural daylight is blue-green. For greater penetration it is best to

work at around noon, when sunlight is closest to a right angle to the water and there is less

reflection off the surface. Below 10 m, the blue-green cast can be photographically corrected by

filtering, using 30 or 40R filters for example. Ultimately, the corrective filtration will depend on

depth and water turbidity. Automatic white point correction can be problematic when using

most digital cameras. Often white balanced underwater images have a pink or purple cast and

look unnatural. Shooting at RAW image format can help digital post-shooting white point

correction. If you want to shoot general views, for which only natural daylight is appropriate,

better shoot in shallow waters (Figure 13.11). For close work and at depths where only blue

twilight remains flash, strobes and battery lamps are the only satisfactory ways to show bright,

faithful subject colours. Be also aware that water turbidity and the concentration of suspended

matter, such as plankton, will

introduce backscatter of any incident

light. Loss of visibility underwater is

largely due to backscatter, so is loss

in contrast. To avoid backscatter, you

have to move the light source away

from your camera. A waterproof

flashgun on a long-jointed arm,

which positions the light well to one

side of the lens axis and closer to the

subject, is the best option. Light

from the flash or strobe should

Figure 13.11 Diver working with a camera in an underwater casing. Water ideally supplement the existing light
filters out longer wavelengths from daylight, giving a typical blue/cyan cast. unless you shoot in caves or
Fit a compensating reddish filter or shoot with flash to render the colours shipwrecks where daylight is non-
faithfully. existent. However, synchro-sunlight

is virtually impossible underwater

unless the water surface is included in the shot.

There are two approaches to underwater camera equipment. Most often, an underwater

housing for conventional cameras, such as a 35 mm, digital SLRs or compact cameras, is used.

Here rods attached to the main camera controls pass through the casing to oversize knobs on

the outside and access the controls inside (Figure 13.12). Such housings can be expensive but

safe down to depths of around 40 m, ample for practically all professional sub-aqua assignments.

They also have connectors to attach external flash units. Housings allow the lens to look through

a domed port, or a flat port. Dome ports are used for wide-angle lenses, the curvature of the

dome is ideally matched to the lens’s focal length. The dome creates a virtual image that lens

focuses on. Often a dioptric supplementary lens is required on the camera to facilitate this. Dome

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ports do not introduce problems associated with refraction, radial distortion and axial chromatic
aberrations (see page 44). Flat ports are used with long lenses for close-ups or shots that start or
end above the water; they do not require a dioptre. Flat ports are unable to correct for the
distortion produced by the differences between the indexes of light refraction in air and water.
They introduce refraction, distortion and chromatic aberration problems when used underwater

(see Figure 13.13).
In some cases the housings are made with

other additional optics to make the apparent

Figure 13.12 Digital SLR camera housing, with flash on a Figure 13.13 When a flat glass port is used on an underwater
long adjustable extension arm. Flash should not be directed housing (top and centre) oblique image light is distorted. Domed
from the camera, but from well to one side. port (bottom) presents the glass at right angles to all rays.

angle of view wider. This is particularly useful to some digital cameras with small sensors that do
not achieve wide angles of view with the conventional lenses. Both wide angle and close-up
supplementary lenses are available, often as ‘wet lenses’ that can be added or removed underwater.

Alternatively, you can use a 35 mm film camera system specially designed with a waterproof
metal body and lens, such as the Nikonos produced by Nikon. These cameras became obsolete in
2001 but are still the preferred choice of some keen underwater photographers. Amphibious
cameras are nowadays made by Sea & Sea, Reef and other manufacturers. Otherwise, digital
underwater cameras are often ‘normal’ cameras provided together with waterproof housing and
settings such as focus, exposure programs and flash modes, for both land and underwater
photography.

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All lenses narrow their angle of view by 30% when used in water instead of air. For

example, an extreme focal length type, such as a 21 mm on a 35 mm camera reduces its angle of

view to that of a 30 mm lens in air. All other lenses tend to be of shorter rather than longer focal

length, because you need to minimize your distance from the subject due to lack of clarity

underwater (Figure 13.14). Wide-angle lenses are by far the most useful choice underwater. They

allow you to get everything in from a shorter lens-to-subject distance, so you suffer less light loss

and contrast flattening from particle backscattering. Macro lenses are also useful, as the subject

is often only inches away from the camera (Figure 13.15). With macro lenses, distortions caused

by refraction are not an issue. Note that when using macro lenses, you are more likely to use

strobe light for the exposure.

The subject will often be too

close to the lens and the

available sunlight will

probably not suffice. A strobe

is required for correct colour

balance at all depths below

about 3 m if accurate colour

rendition is required.

Otherwise, most underwater

camera lenses do not give

satisfactory quality on land

(the scale of focusing

distances also alters).

However, if the camera

Figure 13.14 Ken MacLennan Brown shot this life size picture of juvenile squid on Fuji accepts a range of
Velvia film, with a 35 mm Nikon F90x, equipped with a 105 mm lens in Subal housing. interchangeable lenses, one of

these is likely to be designed

for use in non-underwater

situations such as surfing and

other marine sports.

Finally, wear the smallest

volume face mask so that you

can get your eye as close as

possible to the eyepiece. If

possible, change the regular

SLR pentaprism for a sports

action optical viewfinder –

this lets you see the whole

focusing screen from several

inches away. Good housings

will provide viewfinder

Figure 13.15 Image shot with a Nikon D80 camera in a Sea&Sea housing. The lens was correction optics to aid
a Nikkor macro 60 mm and the subject was lit with a flash. ISO 100, 1/125 second, f/11. underwater use. Compact
Photograph by Muna Muammar. cameras often have a sports

finder.

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