Underwater Photography Tips: Fluorescence

"Fluoro" photography is the latest craze, and has taken the underwater photography world by storm in the last couple of years as new fluorescent photography equipment has become more easily accessible.

'UV/glow/fluoro night dives' are fast becoming a popular activity at dive centers and resorts around the world – allowing divers and snorkellers to experience coral reefs in a unique way, using special dive lights and mask filters to observe this surreal phenomenon.

Some species of coral and other marine animals fluoresce under certain wavelengths of light due to fluorescent photoproteins in their tissues. Ultra-violet (UV) light and blue light (short wavelengths of 400–500nm) is absorbed by these photoproteins, the most common being green fluorescent protein (GFP), and is then re-emitted as green, yellow, orange or red fluorescence (longer wavelengths of 500–700nm). This is different to phosphorescence (where plankton for example can store light energy and emit it again over time), and bioluminescence (where an anglerfish for example can release light energy by a chemical reaction).

Despite being known since the 1930s, research into this phenomenon is still in its early days, and a number of possible theories have been proposed by scientists as to why marine animals fluoresce. Fluorescence could act as a sunscreen protecting corals in shallow water from UV radiation which can cause coral bleaching, while corals in deeper water might use fluorescent proteins to transform blue light (the only light available at depth) into wavelengths which the coral's symbiotic algae can use for photosynthesis. Fluorescence in certain reef fish could help to camouflage them against their fluorescent backgrounds, making them less susceptible to predation.

Charles Mazel (founder of Nightsea) was a pioneer in experimenting with underwater fluorescence photography during the 1970s, and the legendary photographer David Doubilet was one of the first to publish high-quality images of fluorescent corals in the wild in an article for National Geographic in 1997.

"Fluoro" underwater photography relies heavily on specialized equipment and can be a tricky technique to master, but often with extraordinary images as a result. Fluorescence can be seen and photographed during the day, but for the most dazzling and contrasting images, it is most commonly shot at night. Here are some tips to help you get started.

Equipment
You'll need to attach blue "excitation" filters on your strobe(s), or use very bright UV or deep blue lights, to stimulate fluorescence – removing green, yellow, and red wavelengths of white/visible light. (Note: blue light is believed to be more effective than UV light in exciting the fluorescent photoproteins, and therefore better for photography). A yellow "barrier" filter on your camera lens or housing's port then blocks the excitation blue light, allowing green, yellow, orange, and red fluorescence to be recorded onto the camera's sensor. A yellow mask filter will allow you to see much more fluorescence than without one while scanning the reef with a blue spotting/focus light, but may not be needed on your mask when you're actually shooting. You'll need a bright blue focus light (such as the SeaLife Sea Dragon Fluoro Dual Beam, Nightsea Light & Motion SOLA, or Dryon Solaris UV lights), enabling you to focus on your subject – at night, with a darker yellow filter on your lens/port, it can be very difficult to see your subject clearly through the viewfinder and focus. Don't use a white focus light unless it's triggered to turn off instantly as you take a shot, as this will ruin your image. Special blue lights such as the SeaLife Sea Dragon Fluoro Dual Beam have different power settings which is useful, and can also have an attached phosphor filter to quickly convert it to normal white light for use as a primary dive light when needed. These special lights can be expensive though, so a cheaper option is to use a blue filter on a normal, powerful dive light.

Companies such as Nightsea, Glow Dive, Dryon, and SeaLife in conjunction with Fire Dive Gear all make various blue or UV lights, and filters for shooting fluorescence underwater. Manufacturers lights and filters are carefully tuned to match each other's properties, such as the excitation and barrier wavelengths for example, and mixing fluoro equipment from different manufacturers could give frustrating results, believe me! However, in some situations this can be a good thing, as mixing these could allow for more creative lighting – by allowing a small amount of the excitation (blue) light through you can brighten up the scene which would otherwise be very dark, but too much of this could actually hide weaker fluorescence.

Macro is the most obvious choice for shooting fluoro at night, and a 60mm macro lens may be a better choice than a 105mm, for example, allowing you to get closer to your subject for optimal lighting, as well as easier focusing. For supermacro use a 100mm or 105mm lens with a close-up diopter (eg. Subsee +10) – yellow barrier filters are available specifically for various wet diopters that attach to your macro port. Wide-angle fluoro is also possible, with 77mm yellow barrier filters available for rectilinear lenses. However, if using a fisheye lens (e.g., Tokina 10-17mm) with a mini-dome port, then a large square yellow barrier filter needs to be fitted in front of the port – this isn't ideal, as vignetting still occurs, and the reflection of the strobe light on the inside of the filter can mess up your image (since your strobes need to be tucked in quite close to your camera and subject).

Shooting Fuoro
Camera settings will vary depending on which brand of filters and blue light you're using. For example, the Nightsea blue strobe filters are thick and very dark, meaning you'll need your strobes on full power, and possibly still need a high ISO, low f-stop, and slower shutter speed! In comparison, the Glow Dive filters are thinner and lighter, allowing for a lower ISO, faster shutter speed, and slightly lower powered strobes – which could make for sharper images better for printing.

With all the filters you're using on a fluoro night dive, everything is much darker! As a general rule for fluoro photography, you'll need your strobes on a higher power than usual, use a bigger aperture (low f-stop) with a shallow depth-of-field, and push your ISO higher – the downside of shooting fluoro is the grainy 'noise' in your images when using high ISOs. Tuck your strobes in for macro, and pointing directly at your subject. If you're attempting wide-angle fluorescent photography, get close to your subject (most likely coral), and even using a third strobe may be necessary for lighting the larger scene.

Depending on your type of filters and blue spotting/focus lights, subjects could look slightly different to your eye compared to how they look in your RAW image. In my experience, I've found that a fair amount of post-processing (with Lightroom or Photoshop) may be required to achieve a decent final look for certain subjects, to match what you actually saw underwater.

Shooting fluoro on a night dive and moving around with blue light, you'll have less ambient light than you're normally used to (when diving with a typical white dive light), so be careful on a fragile reef and be sure to maintain good buoyancy, and use a pointer/stick to help keep you stable when needed. Avoid stray light from other diver's normal dive lights as this will disrupt the fluorescence you're trying to capture with your camera set-up.

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Subjects

Swimming around on a night dive with a yellow mask filter and a bright blue spotting light, it's actually very easy to find fluorescent subjects because they stand out clearly from far away, dazzling in the pitch blackness – like the most flamboyantly dressed dancer in a dark UV-lit nightclub, you can't miss them! For example, tiny, camouflaged crabs and shrimps which are difficult to find during the day can be spotted from a few meters away.

The surfaces and polyps of corals are easy subjects to start with, and at night the coral polyps open up to feed. However, not all corals fluoresce, and the amount of light they emit can vary between individuals so search around the reef for a decent patch of fluorescing coral, aiming to capture a coral "glowing" from within.

Many corals and other animals "green-wash" when they fluoresce due to the more common green photoprotein, and this can get a bit boring after a while! Subjects with yellow, orange, or red fluorescence (even purple and blue in some subjects) are the most photogenic so keep an eye out for these.

Shooting wide-angle fluoro, you're limited to shooting a smaller range of subjects compared to macro – hard corals are the most common wide-angle fluoro subjects, most of which "green-wash," whereas more photogenic macro subjects may fluoresce yellow, orange, or red.

In addition to corals, a range of other marine animals also fluoresces, which you should look for, with many more fluorescing species no doubt to be discovered. These include: sponges, anemones, jellyfish, clams, flatworms, nudibranchs, octopus, tunicates, crabs, seahorses, scorpionfish, frogfish, lizardfish, goatfish, gobies, flounder, mantis shrimp and other shrimps, and moray eels. Get out there with your fluoro kit and see what you can add to this list!

Fluoro photography will liven up your night dives with a strange 80's disco feel, and can produce unique, psychedelic images. This interesting lighting technique is still relatively new to most underwater photographers so there's still a lot of scope for experimentation, which is a rare thing to find nowadays. Furthermore, the discovery of more marine animals that fluoresce will help to further improve the scientific understanding of this natural phenomenon.

Christian Loader is a full-time professional photographer for Scubazoo Images. He has worked extensively throughout Southeast Asia as an underwater videographer and photographer for Scubazoo since 2007, and lives in Kota Kinabalu, Sabah, Malaysian Borneo.