The Most Important Underwater Accessory

Introduction

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 should I spend $1000 on a strobe when I could get one for $250? We'll explain why strobes are necessary in the first place and then detail the important features separating one price point from another.

Why are strobes critical for underwater work? The short flash duration freezes motion. But even more importantly, 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 acts as a green filter, this is because of the algae growth in the water column. Digital sensors and film are both 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 through the blue or green to restore true color. Strobes are the best lights to use, because their color temperature (the 'flavor' of the light they emit) is the same as daylight. Even so, if the subject is beyond 4.5' (1.5m) from the lens, the water will act 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.

Available light photos look like they were captured with a blue filter	Using a flash brings back the bright colors

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 though the water appears clear to us. Because a camera's built-in flash is so close to the lens, the light travels straight through the water column, and illuminates the particles, which reflect the light 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, those unsightly reflections are deflected from the lens, avoiding backscatter. Divers with bad neutral buoyancy technique can make the backscatter problem worse by kicking up silt. Because of this, neutral buoyancy is a very important skill for the underwater photographer to master. Between avoiding both color loss and backscatter, it becomes apparent that an external strobe is not an underwater photography luxury but a real necessity. But which one to choose? Let's examine the primary features and their underwater advantages.

Backscatter can ruin your photo	Proper lighting and diving techniques will help avoid backscatter

Flash Sync

In order for the flash to fire when the camera shutter opens, it needs 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. When 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 the inside of the housing	O-ring sealed sync cord attaches to the housings bulkhead	Sync cord attaches to the strobe

Most of today's point & shoot cameras, however, do not have a hot shoe connection. For these cameras, the strobe must 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 before the flash that takes the photo; this pre-flash is so fast you don't notice it. If your slave trigger is not designed to ignore this pre-flash, 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.

Dual Fiber Optic cable ports on Olympus SLR housing	Ikelite’s Manual Controller is also a slave trigger

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 SL961 and Sea & Sea YS-27. Higher end strobes, including the Epoque ES-150DS, ES-230DS, Sea & Sea YS-110a and YS-250, 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. Also some SLR housings including the Olympus PT-E05 accept fiber optic cables or a sync cord. Fiber optic cables are reliable and a very efficient way to fire your flash. Since they are a wet connect, they remove a possible failure point on both the housing and strobe. Ikelite strobes, including the DS-160, DS-51 and DS-200, do not have a built-in slave but an optional slave can be connected to the strobe’s 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-17 has a slave trigger but no sync cord connector	Sea & Sea YS-250 has a slave trigger and a sync cord connector	Ikelite’s strobes have a sync cord connector but require an optional 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. Nevertheless, 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. This is a very handy feature: when shooting in manual flash mode you can change your power setting instead of changing your f-stop or strobe-to-subject-distance. All current Sea & Sea strobes along with the Sealife SL961 have this feature. The Ikelite DS-200 have 1/2, 1/4, and 1/8th power settings. You can attach the optional EV Controller to the DS-160 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

Negative space can fool TTL and overexpose the subject. Here manual exposure control was used	TTL works best with macro work, were the subject fills the frame

TTL stands for Through The Lens. In TTL systems, the exposure information that the camera sends to the strobe 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. Other photographers 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.

All recent Ikelite SLR housings are TTL compatible when using their DS series strobes. 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. Aqua Tech solves the TTL problem a different way: they produce housings for land strobes. 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.

The Sea & Sea YS-110a strobe provides what they term DS-TTL when using the fiber optic cable with point & shoot cameras. The strobe uses information from the camera's pre-flash to determine its light output. The Olympus UFL-2 underwater flash also supports TTL through the fiber optic cable. This flash even has a remote control mode that allows you to control the strobe’s power from the back of the Olympus E-520 and E-620 cameras.

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

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.

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 – thereby 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. 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, have dual bulkheads allowing you to connect two sync cords. 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.

Two strobes set on different power settings can produce interesting lighting effects	Dual bulkheads on Aquatica housing

Recycle Time and Batteries

When a strobe fires, it takes a certain amount 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.

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 than the specified recycle time. One of the factors affecting recycle time is the kind of battery that powers the flash. The Ikelite DS-160 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 on 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 in the one you are using. In comparison, the Sea & Sea YS-110a takes AA batteries. Alkaline AA batteries are readily available almost anywhere, but the strobe needs 2.5 seconds to recycle and you get only 230 pops at full power. If you switch to rechargeable NiMH AA's, the strobe will recycle in only 1.9 seconds and you will get 330 pops at full power. If you're doing an expedition where 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 incorrectly aim the strobe 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-200 has an aiming light that uses 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 this strobe in this situation, you might need to turn off the aiming light before shooting. The Sea & Sea YS-110a, and YS-250 use an 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. The Ikelite DS-160 also has an LED aiming light. Another benefit of aiming lights is that they will also help your auto-focus camera work in low light environments.

Halogen bulb aiming light	LED aiming light

Arms and Camera Trays

Once you've decided on the best strobe 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 on each end. They are then joined together with a ball clamp. Each segment can be moved independently and can be extended or folded against itself. This allows for 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 can also use a ball head adapter attached to the top ball segment with a ball clamp. 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 sets only.

Aquatica TLC Ball-Joint Arm	Fantasea Flexi arm	Ball head adapters allow the strobe head to be positioned without moving the whole arm

Flexi arms consist of a group of interlocking pieces that can be moved into different positions. Sea & Sea, Epoque, Ikelite 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.

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.

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. Fantasea, and Nocturnal Lights have a connector, so you can mount their arms on the Ikelite handle. Sea & Sea, and Aquatica housings have a place to attach a dovetail base on top of the housings handles. Then the arms slide onto the dovetail and a set screw holds them in place. Some photographers prefer to attach a ball directly to the housing. They then attach a Ball Joint arm with a ball clamp.

Ikelite arm being attached to quick release handle	TLC arm being attached to dovetail on handle	TLC arm being attached directly to housing

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. 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.

Tray being attached to housing	Flexi arm being attached to tray

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!!

Share your underwater photos with all your friends

Larry Cohen has worked as a studio and location photographer since the late 70's. His clients included Baccarat Crystal, Fuji, Kodak, Sony, General Electric, Time Warner and others. His underwater photos have appeared in such publications as Sport Diver, Immersed Magazine, Sub Aqua Journal, Alert Diver and Northeast Dive News. His photos have also appeared in books such as National Audubon Society Field Guide to Tropical Marine Fishes. In order to extend bottom time and to get closer to marine life he now dives with a Closed Circuit Rebreather. Larry is a founding member of the New York Underwater Photo Society. He is the current president of The NYC Sea Gypsies dive club and is on the executive committee of Oceanblue Divers dive club in Manhattan. At B&H Photo, Larry is a technical writer.

Visit Larry's site at www.liquidimagesuw.com