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Technical

May 2008

When shooting underwater the flat or macro port narrows the field of view (angle of coverage) and therefore increases magnification of the lens, which can be used advantageously with macro and telephoto photography.

The Canon range of macro lenses – the EF50mm f/2.5 Macro, EF-S60mm f/2.8 Macro USM, MP-E65 f/2.8 1-5x Macro, EF100mm f/2.8 Macro USM, and EF180mm f/3.5L Macro USM – often outperform many of their rivals. A supplementary close-up lenses or dioptre can be added to the camera’s primary lens (except for the EF15mm f/2.8 Fisheye) to give a closer focusing range, but in general this reduces the depth of field, and degrades the optical performance of the lens.

© Helen Atkinson

Grouper shot at 30m in cave at Puerto del Carmen, Lanzarote, with one flash and 10-22mm wideangle lens.

Canon’s achromatic dioptres minimise the loss of picture quality, where as a single element close-up lens would result in inferior images. Housing manufacturers also make a range of dioptres that will achieve very good results. And the split dioptres are helpful when photographing half under and half above the surface of the water. The weight of any lens is not an issue when housed underwater.

The fast USM internal autofocusing is virtually silent so it won’t scare fish away, but bubbles you produce (unless using a semi-closed re-breather or a fully closed system) will. In extreme low light (e.g. under rocks) the lens will hunt to focus, but with the help of your dive buddy, an underwater torch should provide enough light for focusing.

When using some digital SLRs underwater, the refracted magnification combined with the digitally extended focal length gives a greater magnification of the subject and means that the photographer can get the desired image results from further away, thus ensuring that there's no disturbance of the fragile marine life.

© Helen Atkinson

Comber (Cabrilla rubia) fish shot at 20m deep using an EF100mm f/2.8 Macro USM lens with two flashguns to light subject.

Don’t forget that macro lenses also have focal lengths, although the physics says that the best results are achieved with minimal water between the subject and lens, this type of lens can be very beneficial when photographing moving subjects that shy away when you get too close, or dangerous underwater life like sharks! Having crystal clear water and bright natural light will help with this. Alternatively powerful flashguns mounted either side of the camera will help.

Extension tubes can be used with other lenses to achieve macro, but can result in significant reduction of image quality. Other lenses can be used successfully with the flat port and port extension rings. Remember the actual focal length will be greater than that of the lens and vignetting will occur with wider lenses used with the flat port.

© Helen Atkinson

Diagram showing how light is reflected off and diffused in water.

The key to taking the best underwater photographs is to know exactly how water, light, and cameras react together. Sunlight is refracted, diffused, reflected, and absorbed in water. The type and brightness of light available underwater is also dependent upon the time of day and the weather conditions.

Rough waters reflect more rays than calm, so wider apertures or longer exposures are needed to capture the natural light. Rough conditions often make for low visibility and a good approach is to use a wideangle lens, such as Canon’s EF15mm f/2.8 Fisheye, and get close to your subject, or use off-camera flash. Macro photography can also be attempted in these situations, but not always successful if there are a lot of particles in the water.

Between about 10am and noon the sun is overhead and in calm conditions these rays will have the least reflection, thus providing the most light for shooting. This is ideal for shots in the shallows, near rocky shorelines and coral reefs where underwater life is found in abundance.

© Helen Atkinson

Diagram showing the differing colour and light loss experienced at various depths.

Polarization of light is greatest in the early morning and late afternoon, when the sun is low in the sky. The effect is to make objects less shiny and more colourful, and is good for photographing the deep colours of shiny fishes, but the light may not be so bright, so shooting at shallower depths can be more beneficial here.

Greater depths absorb more light, resulting in colour and light loss starting with red, then progressing through the colour spectrum through orange, yellow, green, blue, and purple the deeper you go. Generally red or magenta filters can be used to correct the loss of colour in shallow depths. In other words the red filter will remove the blue effect in tropical waters, and magenta filters the green in temperate waters.

© Helen Atkinson

White slate that’s used to help correct white balance for minimising colour loss underwater.

As a result of using filters you may lose a stop of light, but on digital SLR cameras setting a correct white balance using a plastic white or grey slate before shooting will rectify this colour loss without the need for filters or computer optimisation.

If you want to create monochromatic shots your subject needs to stand out in relation to the background, for example the picture of the deep wreck with divers.

With the sun slightly behind you can capture the rich, intense, darker colours of the ocean and your subject will stand out against this backdrop; alternatively you can tilt your camera in the direction of the light to capture lighter pastel shades, or you can create a silhouette of your subject with the sun directly behind.

© Helen Atkinson

Deep wreck with divers shows an example of monochromatic shooting.

The one downfall with digital SLRs compared to film-based SLRs is shooting sunbursts. Even with a 15mm or wider fisheye lens, when stopped down the sensors struggle to capture the burst of light, and tend to white out, but I believe better results can be achieved with the EOS-1Ds system.

Generally, low visibility, shooting in the shadows, venturing deeper, and shooting at night, all require a different approach to lighting, due to the loss of light, colour and contrast – the solution: artificial light such as torch or flash.

The easiest way to light your picture is with a torch, also imperative for focusing. This can create very moody artistic effects on both wide and longer lenses; however you will need excellent buoyancy control, a surface (like the sand or rocks with no aquatic life to damage) for support and extremely steady hands to avoid camera shake, and not forgetting your buddy who can also help to steady you and light your subject with the torch!

There are a variety of flash systems to choose from underwater. Many of the new housings now incorporate an ETTL system to sync flashguns with the camera. Ikelite provides a service where it will upgrade non-TTL housings, and certain strobes to work with the new TTL circuitry.

© Helen Atkinson

Helen Atkinson with Ikelite housing for Canon EOS kit and two Ikelite strobes.

While some manufacturers make housings for Canon Speedlite flashguns, dedicated amphibious flashguns are more popular. Whatever system you choose, it is important to check the sync speed of the flashgun before use.

Using any flashgun manually also works well utilising the rear LCD screen to evaluate the exposure, and adjust flash, aperture and shutter settings accordingly.

Different effects can be achieved with one, two or more flashguns, and by diffusing the light with the addition of a white plastic cover over the strobe. One gun will usually need to be cabled to the housing, the others can then be either cabled or triggered by flash slave (depending on the model).

Backscatter can be one of the biggest problems in underwater photography. Positioning the flashgun on top of the camera is a frequent cause of this. The solution: to position the gun a distance away from the lens (any direction – just experiment and see the results on the LCD), so there is a angle of light hitting the subject is greater than it would be when positioned on top of the camera.

© Helen Atkinson

Blue Ascidian shot with EF100mm f/2.8 Macro USM lens and two flashguns at around 18m deep.

For example: to avoid backscatter and light your subject evenly from the front (direction of light from camera) you need two flashguns. The ideal positioning of these is mounted either side of the camera, on arms which are bracketed to the housing, and pointed straight ahead, but slightly back from the lens to avoid flare.

Manufacturers such as Inon make lightweight aluminium ball joint arms (they are detachable and fully adjustable) that can be used with different housings and flash heads. With some housings the Inon arms have a quick release system giving you the option to try different angles of lighting.

Wideangle shots of fish life on reefs can be achieved by independent metering of the background ambient light and then matching the flash exposure by moving the guns closer or further away from the subject, assuming it doesn’t swim away permanently.

© Helen Atkinson

Fire worm shot on volcanic reef.

Flash is essential in macro photography, where two guns are frequently used, but working with one gun can create very moody images with both macro and wide lenses. Experimentation with direction and positioning is best tried out on a rock before approaching living organisms in order to minimise the risk of damage to them – many sea creatures are especially sensitive to bright light, in particular sea horses which can be blinded.

Salt water is the most corrosive on electric circuits, so having chosen your camera and housing special care and regular maintenance should be undertaken to minimise the risk of flooding. With larger digital SLR systems this can be very time consuming.

Before you dive or use the camera around water, it’s best to clean the seals and o-ring (gently without stretching them) with a lint free cloth to remove any dust or particles, and then lightly grease the o-ring. It is worth noting that the finest of hairs trapped in the seals can cause a leak. The housed camera should then be tested for leaks in a bucket of cold fresh water before being put into operation.

To prevent damaging your equipment avoid hard knocks, and accidental opening. Always keep it out of direct sun and heat to reduce the risk of condensation and heat expansion, which will expand the seals and eventually flood the equipment. When entering the water, from a pier or a boat it is better not to jump in with the housing, but get someone to pass it to you after you have entered, that way the likelihood of leaks will be reduced.

© Helen Atkinson

Parrot fish photographed feeding on sea urchins.

After your underwater shoot it’s important to rinse off and thoroughly soak the housing with fresh water, probably for about 20 minutes to ensure all the salt water is removed from the equipment. Finally the gear can be left to dry out of the sun and heat before being opened to retrieve your shots.

O-rings are silicone, synthetic rubber or neoprene rings used to seal joints in underwater camera equipment making them water tight. The preferred lubricant for silicone O-rings is ‘Fluorosilicone Grease’ (manufactured by Molykote), which is not to be confused with Silicone Grease.

Silicone Grease is a lubricant for NBR (black nitrile) and other non-silicone O-rings and it is highly water repellent. It doesn't cause any swelling or softening. Its other use is to eliminate corrosion and seizure problems on lighting brackets and other metal parts (particularly screw threads).

© Helen Atkinson

Anemone shot on coral reef with surrounding fish showing movement.

Apply a thin layer of fluorosicone grease to the o-ring using your fingers, and make sure that the coating is evenly distributed without any fine hairs or particles before returning to seal the housing.

When storing your underwater system ensure that the o-rings are removed from the housing, flashguns and ports. That way they are more likely to retain their shape for the next use, and not be overstretched. It is also beneficial to apply a thin layer of fluorosicone grease to the o-ring to help preserve it over the time it is not in use.

Safety comes first! Before you attempt to photograph with full dive gear underwater, get properly qualified, not only for your own safety but for that of your buddy, fellow divers, and guide.

It’s worth acquiring some knowledge about the sea life you want to photograph: sea horses can be blinded by flash photography, and it can make sharks unhappy too!

© Helen Atkinson

Diver approaching ray at 20m deep, shot taken wideangle using natural light in RAW file format with white balance taken prior to shooting.

Even with the best laid plans, there are so many variables in underwater photography be ready for the unexpected, and should your housing flood (with good care and maintenance of course it won’t), don’t panic, abort your dive and return as normal to the surface. There are so many variables and limitations in the marine world and also with underwater photography equipment. The best way to enjoy the experience and get good results is attain a good operational knowledge of all your equipment and properly care and maintain it to avoid problems on a dive.

Before you approach your subject think about what you want to achieve with composition and lighting, and be aware of the limitations of current, depth, air and time, and your buddy. Taking photographs is a better way to preserve and remember the environment rather than taking mementos from it. Above all respect the natural habitat, enjoy the underwater experience and have fun with your underwater photography.


Underwater photography - key terms
Acrylic Poly methyl methacrylate. A clear plastic with good optical properties. Used for many dome ports.
Backscatter light reflected in the lens from suspended particles in the water (looks like snow in photographs).
Buddy your scuba diving partner (and essential underwater photography assistant).
Buoyancy control the ability to control where you are in the water.
Chromatic aberration the formation of coloured fringes on an image due to the differences in refraction of different wavelength light by a lens. An achromatic lens may be used to correct this aberration.
Diopter a unit used to express the power of magnifying glasses. Also used as a name for screw in magnifying lenses, which can be fitted to the front of a camera lens.
Dome port a semi spherical piece of acrylic or glass used to eliminate the magnifying distortion caused by reflection – this attaches to the housing and encases your wideangle lens.
Flare unwanted streaks of light on your photos caused by lens imperfection and/or pointing the camera at the light source.
Flat port a flat front element of acrylic or glass and tube which encases your macro or long lens and attaches to the housing.
Fogging misting up of the port element due to condensation inside the housing.
Housing an acrylic, aluminium or alloy watertight box that encases your SLR camera.
Macro lens an extreme close-up lens.
Neutrally buoyant the position where you neither sink nor float.
O-rings silicone, synthetic rubber or neoprene rings used to seal joints in underwater camera equipment making them water tight.
Radial distortion alteration in magnification measured from the centre of the len’s field of vision outwards in a radial direction.
Refraction bending of rays of light as they pass from one medium into another, for example from air to water or air to glass.
Wideangle lens lens that has an angle of view significantly wider than a normal human perspective, typically less than 28mm (on a 35mm SLR system).
Further reading & viewing
The Underwater Photographer by Martin Edge
Underwater Photography by Paul Kay
An Essential Guide to Digital Underwater Photography by Michael Aw and Matthew Muir
Water Light Time by David Doubilet
Diving the World photography by Norbert Wu
Dive Atlas of the World: an illustrated reference to the best sites edited by Jack Jackson
Coral Reef Adventure (MacGillivray Freeman’s) high definition DVD
Recommended dive sites
Australia, Great Barrier Reef www.prodive-cairns.com.au
Canary Islands, Lanzarote www.rubicondiving.com
Global, Padi Dive Centres www.padi.com
Greece, Parga www.poseidondiving.gr
Jordan, Red Sea, Aquaba www.rdc.jo
Nungwi, Zanzibar, and Tanzania www.sensationdivers.com
UK anywhere with a drysuit!