Starting
Out in Underwater Photography
You don't need to be an expert photographer or a SCUBA diver
to take underwater photographs or use a camcorder underwater;
but if you're new to the game, this section may help you to understand
what all of the equipment does and give you an idea of how to
use it and look after it.
Housings:
Any piece of electronic or delicate mechanical equipment destined
to be used underwater requires a housing, i.e., a sealed box
or casing designed to prevent the water from getting in. The
housing can either be part of the equipment, such as the casing
of a waterproof camera; or it can be a separate item designed
to enclose a piece of equipment which is not otherwise waterproof.
There are two basic types of housing: flexible housings, and
hard (or pressure-resistant) housings. In the picture below;
'A' is a small video camera inside a flexible housing,
'B' is a waterproof camera with its own integral pressure-proof
housing, and 'C' is an ordinary camera inside a pressure
proof housing. |
So, what's all this about pressure?
If you take a rigid box underwater and then make a small hole
in it, the water will not dribble in, but squirt in, with a force
which depends on how deep you are. This phenomenon is due to
the weight of the water above you. On the surface of the planet,
we are always under pressure due to the weight of the atmosphere
above us, but we don't usually notice it because the air-spaces
inside our bodies are at much the same pressure as the air outside.
The only times when you might notice the effects of changing
air pressure are when driving from the top to the bottom of a
large hill, or in an aeroplane which is coming in to land; in
which case, your ears start to feel strange until you yawn or
move your jaw about. This is because, unless you have a very
bad cold, the body has only two air-spaces which are not normally
open to the outside, and these are behind the ear-drums in a
place known as the 'middle ear'. The middle-ear has a tube leading
to the throat, called the 'Eustacian tube', which is opened and
closed by a small muscle called a 'dilator muscle'. The dilator
muscle operates when you yawn, to keep the pressure on both sides
of the ear-drum approximately the same so that you can hear properly.
You'll need to make friends with your Eustacian tube dilator
muscles when you learn to dive or snorkel.
When you dive underwater, the problem
of increasing pressure is much more severe than when you lose
height in the air, because water is so much heavier than air.
The air pressure varies slightly due to the weather, but on an
average day, the pressure of the atmosphere, due to the weight
of the column of air between the surface of the earth and interplanetary
space, is only the same as the pressure due to 9.9 metres of
water. It's not so much the absolute pressure we're interested
in however, but the pressure difference between the inside and
outside of any box or vessel (or ear-drum).
When you close a rigid box on the
surface, the pressure inside is fixed at about atmospheric pressure.
For convenience, we can refer to this pressure as 'one atmosphere'.
When you swim down to a depth of about 10 metres, the pressure
inside the box is still only at one atmosphere (or even less
if the water has caused the air in the box to cool down) but
the pressure outside is 2 atmospheres, i.e., the pressure due
to the atmosphere plus the pressure due to the water.
The pressure difference however, between the inside and the outside
of the box, is one atmosphere. In general, the pressure difference
increases by one atmosphere for every 10 metres (10m) of depth,
i.e., at say 30m, the pressure difference between the inside
and the outside of the box is about 3 atmospheres, but the absolute
pressure (water + air above) is 4 atmospheres.
The above examples were chosen
for their nice round numbers. There is nothing magical about
the pressure of one atmosphere, and it takes only a tiny fraction
of that to cause a housing to leak. In fact, the cooling effect
of plunging a housing into water (which makes the air inside
want to contract) is enough to cause a leak without going to
any depth at all. Fortunately, it is down to the engineers who
design underwater housings to solve this problem for you, but
given the enthusiasm with which the water wants to get in, the
engineers can't help you if you don't take the business of closing
the housing seriously. |
One solution to the pressure problem is to make the housing flexible.
The housing can then simply contract (reduce in volume) to keep
the pressure on the inside and the outside the same. This is
a very reliable system, because the lack of any pressure difference
means that there is no real tendency for the housing to leak.
This system is also very simple, because the controls of the
equipment inside the housing can mostly be operated through the
flexible plastic. There are limitations to this approach however,
because as you go deeper, there will come a point when the housing
clings tightly to whatever is inside it, the housing won't be
able to shrink anymore, and a pressure difference will begin
to appear. Consequently, flexible housings still need to have
a pressure-resistant sealing system. The ewa-marine housings
in the pictures above all use a metal clamp, held together by
hand-tightening screw-fasteners ('hand-wheel nuts'). Closing
the housing is a matter of making sure that the two surfaces
which will be clamped together are clean, since dirt, and particularly
hairs, can make microscopic channels through which the water
can creep. Cleaning the surfaces is simply a matter of wiping
them with a lint-free cloth or paper towel, and inspecting them
carefully before fitting the clamp. When assembled properly,
the sealing system, and the tough flexible plastic material,
can withstand large pressures, 30 or 40 metres of water, and
the real limitation is that of how much punishment the thing
inside the housing can take. With cameras, there comes a point
when the water starts to press buttons which you don't want pressed,
and so the recommended depth limit for flexible housings is usually
(but not always) about 10 metres.
Flexible housings are available
for cameras, video camcorders, personal effects and valuables
(so you can take them with you into the water), mobile phones
and VHF radios (in case you fall into the water), maps and charts,
etc. If you are interested in flexible housings for products
other than cameras, you can find them in the Cameras Underwater weather protection section.
Flexible housings for camcorders are to be found in the video
section, and flexible housings for compact, digital, and single-lens
reflex (SLR) cameras are to be found in the various camera equipment
sections, but you may like to read the information given below
before exploring those pages. |
Hard, Rigid, or Pressure-Resistant Housings:
Hard housings, whether part of a camera, or a separate box into
which the camera must be installed, are nearly always sealed
by means of a device called an O-ring. In fact, there will be
an O-ring seal for every control, and every plug, socket, or
window, in the housing, but the user is mainly concerned with
O-rings (such as the one around the door which gives access to
the camera) which have to be disturbed in some way while the
equipment is being prepared for use. |
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The O-ring itself is simply a rubber band, usually of circular
cross-section, but manufactured to high tolerances so that it
is free from nicks, holes, and other defects which might let
the water into the housing. The O-ring is also made of a particular
type of rubber (there are lots of types), chosen for its chemical
resistance and hardness, and it is not a good idea to use a substitute
unless you know what you are doing. |
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The 'O-ring seal' is the combination of the rubber ring and a
specially shaped groove, which is designed so that, when the
housing is placed under pressure, the ring is forced into the
gap through which water is trying to pass. |
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O-ring with no pressure difference. |
O-ring under pressure. |
The cute thing about this system is that the seal actually gets
tighter as the pressure increases; which means that the seal
is inherently reliable, provided that the O-ring and the
O-ring groove are kept in good condition and are kept thoroughly
clean while the housing is being closed. This is the most important
thing you need to know about underwater photography with hard
housings, because bad husbandry in this department can lead to
serious disappointment, whereas bad photographic technique can
be rectified with practice. There is nothing difficult about
assembling an O-ring seal however; it is simply a matter of cleaning
the O-ring and the groove with a paper towel, inspecting the
surfaces for dirt and hairs, and, for the type of seal shown
above, applying a very thin coating of grease to the O-ring.
The grease used on O-rings incidentally, does not form part of
the seal; its job is simply to make the O-ring slippery so that
it can slide into position without being damaged.
Most manufacturers opt for the
hard-housing approach to underwater equipment design, and a wide
range of underwater cameras, camera housings, camcorder housings,
and torches are available, with depth ratings from 20 metres
to over 100 metres. Information on these items appears on the
Cameras
Underwater Products Website. You can also find out more about
underwater photography by reading the other
articles in this website, or by looking-up terms you don't
understand in the glossary. |
Going underwater:
There are a few people who decide that they would like to take
underwater pictures but have, up until that point, always kept
their eyes tight shut when going under the surface. It is important
to know therefore, that human eyes cannot focus underwater. In
order to be able to see the camera viewfinder, it is necessary
to place an air-space between the eyes and the water. A pair
of swimming goggles will do the trick at shallow depths; but
plastic goggles tend to become scratched and battered, and you
will be able to see much more clearly if you obtain a proper
diving mask with toughened optical-glass lenses. You can obtain
such a mask from any good Diving Equipment Shop, and the staff
there should be able to give advice on choosing the right size
and proper fitting. |
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Masks and goggles also tend to
mist up, and clarity of vision is much more important for photographic
diving than for any other type of diving. A solution to this
problem is to apply the tiniest amount of shampoo to the inside
of the lens, and wash it around with a little water. Since traces
of the detergent will inevitably end-up in your eyes, you must
use a shampoo which doesn't cause the eyes to sting for this
purpose, i.e., baby shampoo, or the type of shampoo where you
have to pay extra to have the noxious chemicals left out. Don't
use medicated shampoo, conditioning (i.e., oily) shampoo, and
don't be tempted to use washing-up (dish) detergent or ordinary
soap. If you have no shampoo with you, saliva (spit) is the traditional
diver's de-fogging agent, but it is not as effective as detergent.
You can take perfectly good photographs
by putting your head just under the water; but to add a feeling
of drama to a photograph, it is sometimes desirable to be on
the same level as, or below, the subject. This means that you
will need to learn how to dive or snorkel, and this brings us
back to the subject of ears. One of the golden rules about swimming
under the water is that there is no acceptable level of pain.
Your Eustacian tubes will not work very efficiently if you have
a cold; and people often have low-grade throat infections which
produce little in the way of symptoms, except for difficulty
in opening the Eustacian tubes. The Eustacian tubes of children
also tend to be inefficient, but these problems usually resolve
naturally by the time children reach their teens. If your Eustacian
tubes do not open as you dive down, you will experience discomfort
at a depth of about 0.5 metres, and actual pain at a depth of
about 1 metre. The only way to resolve this problem is to go
back to the surface and try again. If you carry on down, the
pain will not go away because the pressure difference between
the middle-ear and outside will hold the Eustacian tube shut,
and you will eventually reach a point where one of your ear-drums
will burst.  Don't do it - learn how to get your
Eustacian tubes to work instead.
Opening of the Eustacian tubes
is normally a part of the yawning and swallowing reflexes, which
is why it's a good idea to feed babies while an aircraft is coming
in to land. You can actually yawn without opening your mouth,
and you might try learning how to do this (out of the water)
and using this trick when you dive. When the Eustacian tube to
a particular ear opens, you will hear a 'click' in that ear.
If you hum a note at the same time, the sound of the humming
will become loud as the air-channel between the ear and the throat
opens. With practice, you may find that you can get the opening
of the tubes under conscious control, and separate it completely
from the yawning reflex; after which, diving will become a cinch.
If all else fails however, you can resort to a procedure known
as the 'Valsalva manoeuvre' which involves holding your nose
and blowing (you must also close your mouth or block your snorkel
with your tongue). Diving masks normally have provision for holding
the nose from the outside, so that the Valsalva manoeuvre can
be performed while wearing a mask; but it is not a good idea
to perform this procedure too vigorously if you have a cold,
because you may introduce bacteria into your middle-ear and cause
a painful infection (and temporary deafness). The Valsalva manoevere
should anyway, only be performed gently and tentatively, with
just enough pressure to achieve the desired effect. Coming up
from depth incidentally, is hardly ever a problem, because the
closed Eustacian tube acts as a one-way valve; one of its natural
roles being to allow fluid to drain easily out of the middle-ear,
but make it difficult for things to get in. |
You can find out more about underwater swimming and diving by
contacting training organisations and clubs in your local area.
If you are planning the diving holiday of a lifetime, you may
find that you will get the most pleasure from it by taking a
training course at home before you go.
You can find out more about underwater
photography by reading the other articles
in this website, and by visiting the Cameras Underwater Products Website. If
you don't know what a particular technical term or abbreviation
means, there is a good chance that it will have been added to
the glossary. |
© D. W. Knight, Cameras
Underwater Ltd. 2001, 2002
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