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The Most Important Underwater Accessory

Buying an underwater housing is just the beginning. There are many accessories that are helpful or necessary for taking photos underwater. An external flash, also called a strobe, is your most important accessory. Photography is the art of creating images with light, and while the control of available and artificial light is important for all photography it is especially crucial when shooting underwater. Strobes come in a variety of prices with many different features, and the choices can be confusing for the beginning photographer. You might wonder why you should spend $1000 when you could get a strobe for $250. We'll explain why strobes are needed in the first place and detail the important features separating one pricepoint from another.

Why are strobes critical for underwater work? As you descend underwater, you lose color. The warm colors of the spectrum are lost first, and the problem exacerbates with deeper descents. Warm salt water acts like a giant blue filter over your lens, while cold salt water or fresh water act as a green filter.

Shipwreck shot with available light looks like it was shot with a blue filter
Using a flash brings back the bright colors
Digital sensors and film alike are more sensitive to this effect than the human eye. With the addition of artificial light, however, warm colors are returned to the underwater scene. When white light is used close to your subject, it cuts thought the blue or green to restore true color. Strobes are the best lights to use, as their color temperature (the 'flavor' of the light they emit) is the same as daylight. The short flash duration freezes motion. When the subject is beyond 4.5' (1.5 m) from the lens the water acts as a blue or green filter over your light source, destroying much of the strobe's advantage. So no matter how powerful and expensive your flash, the golden rule of underwater photography is WHEN YOU THINK YOU ARE CLOSE ENOUGH MOVE CLOSER!! This cannot be overstated: the closer you are to your subject, the better your photos will be.

Beyond blue/green color variance, another problem unique to underwater photography is backscatter. The world's oceans and other bodies of water have stuff floating in them, even when appearing clear to our eyes. Because a camera's built-in flash is so close to the lens, the light travels straight thought the water column, illuminates the particles & reflects them back to the lens. This causes an unsightly white speckled effect that looks like snow and is called backscatter. By having an external strobe aimed correctly from the side, the unsightly reflections bounce away from the lens, avoiding backscatter. The backscatter problem is worst in water with poor visibility. Neutral buoyancy is a very important skill for the underwater photographer. Divers with bad neutral buoyancy technique will kick up silt, adding to the backscatter problem.

Between avoiding both color loss and backscatter, it becomes apparent that an external strobe is not an underwater photography luxury but rather a necessity. But which one? Let's examine the primary features and their underwater advantages.

proper lighting and diving techniques could help you to avoid backscatter
Backscatter can ruin your photo

Flash Sync

In order for the flash to fire when the camera shutter opens, they need to be connected in someway. We need to make sure our strobe is compatible with our camera and housing. For single lens reflex cameras and some advanced point & shoot cameras, you would use a sync cord. In these applications, the inside of the housing features a connection which attaches to the camera's hot shoe. This connection leads to a bulkhead which attaches to an o-ring sealed sync cord on the exterior of the housing. The sync is then attached to the strobe. If using a camera/housing combination that uses a sync cord, make sure the strobe you buy has a bulkhead for a sync cord.

Hot shoe connector on inside of housing
O-ring sealed sync cord attaches to housings bulkhead
Sync cord attaches to Strobe

Sea & Sea YS-27 with fiber optic cable and arm
Most of today's point & shoot cameras, however, do not have a hot shoe connection. For these cameras, the strobe needs to have an optical slave trigger. When the camera's on-board flash fires, the light will trigger the strobe. Many digital cameras use a pre-flash to determine proper exposure; these cameras emit a flash that is so fast you don't notice it, to gather information before the flash that takes the photo occurs. If your slave trigger is not designed to ignore this preflash, it will fire your strobe when the camera's shutter is not open. So for most point & shoot digital cameras, it is vital to have a pre-flash compatible slave trigger. Some of these strobes use a fiber optic cable to efficiently move the light from the on-camera flash up to the strobe. Remember, you don't want your on-camera flash to fire on your subject, or you will get the dreaded backscatter.

Ikelite DS-51 with slave trigger pointing at cameras built-in flash
Many economical strobes have built-in pre-flash compatible slave triggers, but do not allow use of sync cords. These includes the Bonica-XP, Fantasea CoolFlash Nano, Sealife SL960D, Sunpak G-Flash, Sea & Sea YS-25 and YS-27. Higher end strobes, including the Sea & Sea YS-90 and YS-110, offer a built-in pre-flash compatible slave trigger as well as a sync cord bulkhead. For people who are planning to start with a point & shoot camera and move up to an SLR once they get more experience, these dual-function strobes are a better option. Ikelite strobes, including the DS-125, DS-51 and DS-200, do not have a built-in slave but an optional slave can be connected to these strobes' sync cord bulkhead. An advantage to this system is that you can use a 15' or 3' extension and have a second strobe behind a diver or hidden behind a coral formation to light up an area. This allows you to light up the background in a cave, or a shadowy area on the side of your scene.

Sea & Sea YS-27 has slave trigger but no sync cord connector
Sea & Sea YS-110 has slave trigger and sync cord connector
Ikelite strobes use a optional slave attached to the strobes bulkhead
Ikelite's Exposure Value Manual Controller is also a slave trigger

Power

How much light a strobe produces is indicated by the strobe's Guide Number or Watt-Seconds rating. Guide numbers really aren't a measurement of power but are instead the maximum flash-to-subject distance when a lens is set to f/1.0 and the ISO speed is 100. Thus, if a flash were rated at a guide number of 100, it would project 100 feet at ISO 100 with a lens aperture of f/1.0, but only 25 feet with a more realistic lens aperture of f/4.0. Some manufactures only give us this specification, so it is all we have to go on. Watt-seconds are also not a unit of light output but rather a unit of electrical usage, but they do give a good idea of how bright our strobe is. Essentially the higher the watt-seconds rating, the more light the strobe produces. Because water is denser than air, you'll need a strobe with some punch-but never forget that the goal is always to be as close to the subject as possible. Some strobes have a dial, to allow seamless increases and decreases in the power

Power dial on YS-110
This is a very handy feature: when shooting in manual flash mode you could change your power setting instead of changing your f-stop or strobe-to-subject-distance. All current Sea & Sea strobes along with the Sealife SL960D and Sunpak G-Flash have this feature. The Ikelite DS-200 and DS-125 have 1/2, 1/4, and 1/8th power settings. You could attach the optional EV Controller to the DS-125 as well as the DS-51 strobe in order to dial down the power in half-stop increments down to 5 stops. The EV Controller also functions as a slave trigger for use with point & shoot cameras. This slave sensor works with both preflash and non-preflash cameras.

TTL and Auto Exposure Control

All the blue water can fool TTL and overexpose the reef
TTL stands for through the lens. In TTL systems, the camera sends exposure information to the strobe which was measured at the digital sensor or film plane instead of some external location upon the camera. For underwater work, this becomes problematic. Usually the strobe is not manufactured by the same company as the camera. Thus, the information needs to be transferred from the camera to the housing's bulkhead, and then up a cable to the strobe.

Generally speaking, TTL works best when shooting in macro mode, or any other time that the subject completely fills the frame. When shooting wide-angle, with abundant negative space in your image, a TTL system will tend to overexpose the subject. Because of these limitations, many photographers believe that in today's digital world TTL is not worth the trouble when shooting underwater. When shooting digitally, many photographers shoot in the camera's manual exposure mode and use the "shoot, review and adjust" method. If your strobe has a power dial this is very easy and gives you lots of control. At the time of this writing, Aquatica does not support TTL, believing it does not benefit the underwater realm. Others feel, however, that allowing the camera and strobe to do the thinking allows the photographer to concentrate on composing that once-in-a-lifetime shot.

Fire worm and background fills frame so TTL works
All recent Ikelite SLR housing are TTL compatible when using their DS strobe series. Sea & Sea requires a TTL converter for most of their housings. The converter is interesting since it has two bulkheads. So you have TTL control over dual Sea & Sea strobes. You can do this with the Ikelite with a dual sync cord. Fantasea and Olympus solve the TTL problem a different way: they produce housings for land strobes. Fantasea produces housings for the SB800 for Nikon, 580EX for Canon and the FL-50 for Olympus. Olympus has a housing for their small but powerful FL-36 strobe. With these setups the strobe and cameras were designed to talk to each other from the beginning. All of the above solutions offer exposure compensation along with the TTL control .This is very important, because it allows you to dial down any overexposures created by the TTL.

Sea & Sea has a optional TTL converter
Fantasea's housing for the Canon 580EX flash
Olympus housing for the FL36 flash

The Sea & Sea YS-110 strobe provides what they term DS-TTL when using the fiber optic cable upon point & shoot cameras. The strobe uses information from the camera's pre-flash to determine its light output. The Fantasea Cool Flash Nano and the Bonica Neon-XP have an auto sensor on the strobe. This sensor measures the amount of light needed for proper exposure at a certain f/stop and cuts the power of the flash when the correct amount of light reaches the subject. If TTL is important to you, make sure your strobe and housing are compatible and they allow TTL control.

Coverage Angle

Sea & Sea YS-110 Dual strobe kit
Because we want to work very close to our subjects, the amount of light coverage is very important. When photographing underwater, aim to shoot with a macro lens for very small subjects or wide-angle lenses for large objects. In this way you will maintain as close a working distance to your subject as possible. So if you're using a wide-angle lens which covers an 80-degree horizontal area, you'll need a strobe with a horizontal illumination angle of at least 80 degrees. Strobes which have a coverage angle of 100 degrees are best suited for wide-angle work. Using a diffuser over the strobe will help to spread the light out over a wider area and give you nice, soft light. It will also help to blend the strobe light with the available light.

Ikelite Dual sync cord
Many experienced underwater photographers use two strobes. With two strobes it becomes easier to cover the area seen by your wide-angle lens. When using two strobes you can also use longer strobe arms to keep the lights further off to the side-keeping the strobe heads away from the center of the scene and reducing backscatter. To achieve a more captivating lighting effect, it is best to use one strobe as the powerful main light with the second strobe used as a weaker fill light.
Two strobes set on different power setting can produce interesting lighting effects
The fill light is for softening the shadows, and shouldn't overpower the main light. The best way to achieve this effect is to have two identical strobes with power dials. With the strobes an equal distance from the subject, you can easily dial in different power settings for variable light ratio effects. Some housings, including Aquatica and Sea & Sea, have dual bulkheads allowing you to connect two sync cords.
Dual bulkhead on Aquatica housing
Ikelite housings have one bulkhead, but they have dual sync cords. These cords have three connectors-one for the camera, and one for the two strobes. It is also possible to have one strobe connected with a sync cord and have the second strobe fired with a slave sensor.

Recycle time and Batteries

When a strobe fires, it takes a certain about of time for the power to build up so the flash can be fired again. This is known as the recycling time. A faster recycle time is always better, for it is very frustrating to have taken a photo and then miss a second, superior photo because the flash won't fire.

Ikelite battery pack for DS-125
Recycle times are given by manufacturers to reflect the time you must wait when the strobe is fired at full power. When shooting at a close distance in TTL mode or when turning down the power, the strobe will recycle much faster then the specified recycle time. One of the factors effecting recycle time is the kind of battery that powers the flash. The Ikelite DS-125 uses a special rechargeable NiMH battery pack. This battery allows the strobe to recycle in only one second after a full power discharge, and it will fire approximately 250 times at full power upon one charge. The disadvantage of this kind of battery is that you need to carry along an expensive backup battery in case you deplete the power before being able to recharge the battery. In comparison, the Sea & Sea YS-110 uses AA batteries. Alkaline AA batteries are readily available almost anywhere, but the strobe takes six seconds to recycle and you get only 160 pops at full power. If you switch to rechargeable NiMH AA's, the strobe will recycle in only three seconds and you will get 320 pops at full power. If you're doing an expedition were it is impossible to recharge batteries, you are better off with a strobe that uses AA batteries.

Aiming Light

Some strobes have a built-in aiming light, which is a constant light source in the middle of the flash tubes which helps you visualize the area the strobe light will illuminate. Since everything underwater looks 25% closer, many new photographers aim the light in front of their subjects. This only exacerbates the backscatter problem, with very little light ending up upon the subject. Built-in aiming lights are helpful in avoiding this problem.

The Ikelite DS-125 and DS -200 have aiming lights that use a halogen bulb. Since the bulb has a warm color temperature it is easy to see, even in bright sunlight. However, if you're very close to your subject and shooting at a slower shutter speed with a wide aperture, you might get a warm color spot in the middle of your image. When using these strobes in this situation, you might need to turn off the aiming light before shooting. The YS-110 uses a LED aiming light. LEDs have the same color temperature as daylight and strobes, but it really doesn't matter since the aiming light goes off when the strobe fires. Aiming lights will also help your auto-focus camera work in low light environments.

DS-125 halogen aiming light is very warm in color
YS-110 LED aiming light is daylight balanced

Arms and Camera Trays

Once you've decided on the best strobe for you based on the features you need, you must correctly position your strobe. To achieve this you must attach the strobe to an arm, and attach the arm to your housing.

There are a few different kinds of light arms. Ball Joint and Flexi arms are the most popular. Ball Joint arm sets have two or more segments, with each segment featuring a ball upon each end. They are then joined together with a ball clamp. Each segment can be moved independently from each other and can be extended or folded against itself. This allows for the maximum flexibility in shortening or extending the arm. Aquatica's TLC (Technical Lighting Control) brand arms allow the strobe to be mounted with a strobe head adapter directly to the top segment. You could also use a ball head adapter attached to the top ball segment with a ball clamp.

Ball Head adapter allows strobe to be mounted on to middle arm segment
Aquatica TLC Ball Joint arm
Fantasea Flexi arm

Head adapter allows strobe to be mounted on to upper arm segment
This allows the strobe to be adjusted without moving the whole arm. Aquatica, Ikelite and Fantasea produce Ball Joint arms in sets as well as individual sections. Sea & Sea sells them in sets.

Flexi arms consist of a group of interlocking pieces that can be moved into different positions. Sea & Sea and Fantasea produce these arms. They do not offer the flexibility of the Ball Joint arm but they are economical and easier to use. For macro work you must use shorter arms. Flexi arms are ideally suited to macro work, and for wide-angle work a Ball Joint arm system works best.

YS-110 attached to Flexi arm
Ikelite offers a third kind of arm. The Ikelite Strobe Arm II consists of a 12" tubular strobe arm and a mounting block. The design provides rotation in all directions and allows the tube to slide up and down for length adjustment. The arm provides versatility at a very reasonable cost.
DS-51 attached to Ikelite standard arm with slave senser
After you've chosen an arm set, you must mount the strobe arm to the housing. Most SLR housings allow the arm to mount onto the housing's handle.

Ikelite housings have a handle with a hole for their arms to slip into with a quick release lock. Both Fantasea and Aquatica have a connector, so you could mount their arms on the Ikelite handle. Sea & Sea, Aquatica and most Fantasea housings have a place to attach a Dovetail Base on top of the housings handles. Then the arms slide onto the dovetail and with a set screw gets held into position. Some photographers prefer to attach a ball directly to the housing. They then attach a Ball Joint arm with a ball clamp. For small point & shoot cameras, a tray is attached to the bottom of the housing like a tripod and arms can then be attached to the tray

Ikelite arm being attached to housings quick release handle
TLC arm being attached to dove tail on housing handle
TLC arm attached directly to housing

Sea & Sea's Sea arm light
Sea & Sea's Sea Arm Light has the arm and a tray in one unit. Whatever style of arm you choose, remember the purpose is to position the light. The strobe arm should be an extension of your own arm, rigid yet flexible and responsive.

Fantasea tray being attached to Olympus housing
Fantasea Flexi arm being attached to tray

Share the underwater world with all your friends
Click here to compare features on the many strobes available. Once you've decided upon a strobe and arm configuration, it is time to get wet and start capturing images. With your new housing and lighting you'll bring back amazingly colorful photographs that will astound your non-bubble blowing friends!!

Larry Cohen has been Scuba Diving since 1989. He is the technical writer for all the underwater imaging sections of the B&H Photo web site. His photos have appeared in such publications as Sport Diver, Immersed Magazine, Sub Aqua Journal and North East Dive Journal as well as in books such as National Audubon Society Field Guide to Tropical Marine Fishes. He has crewed on the "The John Jack" a dive boat based on Staten Island, NY. He is a past president and still active member of The NY Sea Gypsies dive club. He also teaches Underwater Photography at Village divers in New York City. www.villagedivers.com

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