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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. B&H carries 50 different strobe packages, so it’s no wonder choosing a strobe could be confusing for the beginning photographer. We'll explain why strobes are necessary in the first place, and then dive into detail about the important features that delineate one from another.
Top two Images: using strobes brings back natural color.
Photographed on the wreck of the Keystorm in the St. Lawrence River.
Why are strobes critical for underwater work? These days, digital cameras can also capture video. Continuous LED lighting could be used for video and stills, but for stills, strobes have a few important advantages. The short flash duration freezes motion. You could also have one available-light exposure for the background and a separate strobe exposure for the subject. This allows for more control and dramatic photographs.
Without strobes, underwater images will have a blue cast.
As you descend deeper underwater, you lose color, because it is filtered by the water. The warm colors of the spectrum are lost first, and the problem is exacerbated with deeper descents. Warm saltwater acts like a giant blue filter over your lens, while cold saltwater or fresh water acts like a green filter because of the algae growth in the water column. Digital sensors are more sensitive to this effect than the human eye, so you may not perceive it the same way your camera does.
This available light photo of a school of fish has a blue cast.
With the addition of artificial light, however, warm colors are returned to an underwater scene—when white light is used close to your subject, it cuts through the blue or green to restore true color. Strobes and LED lights are the best to use, because their color temperature (the “cool” cast 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 white-light advantage. So, no matter how powerful and expensive your flash may be, 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 images will look.
Getting close to your subject is the Golden Rule of underwater photography.
Beyond blue/green color variance, another problem unique to underwater photography is a phenomenon referred to as backscatter. The world's oceans and other bodies of water have particulate matter 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 that's what backscatter is.
External strobes will reduce backscatter.
By having an external strobe aimed correctly, from the side, those unsightly reflections are not aligned with the lens axis, thereby 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, and stopping motion, 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.
For the flash to fire when the camera shutter opens, it needs to be connected to the camera in some way. You need to make sure your strobe is compatible with your camera and housing.
Hot-shoe connection inside a housing
For cameras that have a hot shoe, you could use a sync cord. The inside of the housing has to have a connection that attaches to the camera’s hot shoe. This connection leads to a bulkhead, which has an o-ring-sealed sync cord on the exterior of the housing. The sync is then attached to the strobe. This is the primary method used to sync the strobe to cameras that don’t have a built-in flash or housings that do not allow you to use the camera’s flash.
Waterproof bulkhead connection for sync cord
The problem with this system is that you have four possible failure points—where the housing connects to the camera’s hot shoe, the sync cord at the housing connection, where the sync cord attaches to the strobe could fail, or the sync cord itself, which could break. Both sync cord connections are possible flood points.
For cameras that have a built-in flash that could be fired in the housing, optical slave triggers represent another option. The strobe needs to have a slave trigger—when the camera's onboard flash fires, the light will trigger the strobe. Many digital cameras use a pre-flash to determine proper exposure before the flash 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. For all digital cameras, it is vital to have a pre-flash-compatible slave trigger.
Fiber optic cable
Some strobes have a built-in slave trigger set back, so other people’s strobes do not fire your strobe. These strobes require a fiber optic cable to efficiently move the light from the on-camera flash up to the strobe. Both the strobe and the housing need to have a connection point for the fiber optic cable. Fiber optic cables are reliable and rarely fail. Since they are a wet connect, flooding is not an issue.
Many housings for point-and-shoot, mirrorless, and DSLR cameras now have fiber optic ports built into the housings. For housings that do not have this connection point, one could be added using the Sea & Sea Strobe Mask Set.
Butterfly fish, photographed in Bonaire
Many strobes have built-in pre-flash-compatible slave triggers, but do not allow use of sync cords. This includes the Sea & Sea YS-01, Sea & Sea YS-03, Ikelite AF-35, Sealife Sea Dragon Flash, Fantasea CoolFlash Nano, Fantasea Line Inon S-2000, Ultramax Ultrapower UXDS-3, Ultramax Ultrapower UXDS-1, Olympus UFL-3, and Nikon SB-N10.
Other models, such as the Epoque ES-230DS and higher-end strobes like the Sea & Sea YS-D1 and Sea & Sea YS-250, offer a built-in pre-flash-compatible slave trigger, as well as a sync cord bulkhead. For people who might start with a built-in-flash camera and switch to one that does not have one, these dual-function strobes are a better option.
Ikelite strobes, including the DS161, DS160 and DS51, do not have a built-in slave. The optional Ikelite Fiber-Optic Converter for DS Substrobes can be connected to these strobe’s sync cord bulkheads to turn them into fiber-optic ports. An advantage to this system is that you can use the Ikelite 15' Extension Cord or Ikelite 3' Extension Cord to fire a second remote strobe behind a diver or hidden behind a coral head. This allows you to light up the background in a cave, or backlight your subject.
Using a remote third strobe for backlighting in an underwater cave
The amount of light a strobe produces is indicated by the strobe's Guide Number or Watt-Seconds rating. The guide number is not a measurement of power, but is instead a way to determine the right flash-to-subject distance at a given lens aperture and an ISO speed of 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. 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 the 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.
Strobes with a power dial allow for easy manual exposure control.
Because we want to work very close to our subjects, the amount of light coverage is very important. Underwater, we want to shoot with macro lenses for small subjects and wide-angle lenses for everything else. This way, we maintain a close working distance to the subject. If you're using a wide-angle lens that covers an 80-degree horizontal area, you'll need a strobe with a horizontal illumination angle of at least 80 degrees. Strobes that 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.
Diver with dual Sea & Sea YS-01 strobes
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 use longer strobe arms to keep the lights farther 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 at 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, offer dual bulkheads or fiber optic cable ports, allowing you to connect two strobes. Ikelite DSLR housings have one bulkhead, but dual sync cords could be used. These cords have three connectors; one for the camera and two for the strobes.
TTL and Auto Exposure Control
TTL stands for “Through the Lens.” In TTL systems, the exposure information that the camera sends to the strobe is measured at the digital sensor instead of some external location. For underwater work, this becomes problematic—strobes are frequently not manufactured by the same company as the camera. The information needs to be transferred from the camera to the housing's bulkhead, and then up a cable to the strobe.
TTL exposure control works well on macro photographs.
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. These photographers shoot in 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 control. Other photographers, however, feel that letting the camera and strobe do the thinking allows the photographer to concentrate on composing that once-in-a-lifetime shot.
Use the shutter speed to control the background exposure, and the aperture and strobe power for the subject.
Ikelite DSLR housings are TTL compatible when using the company’s DS-series strobes connected with a sync cord. There is a strobe control on the housing that allows exposure compensation when shooting TTL.
DS-TTL is available with some strobes, including Sea & Sea YS-D1, YS-01, YS-03 the Ikelite AF-35, when using a slave trigger. The strobe uses information from the camera's built-in flash to determine its light output. The Sea & Sea YS-D1 and Ikelite AF-35 have an exposure compensation dial, but you could still adjust the TTL exposure with the YS-01 and YS-03 by using the camera’s built-in flash exposure compensation control.
Sea & Sea Optical YS Converter
Sea & Sea Optical YS Converter/C1 can be used on certain Sea & Sea housings. This device mounts on the camera's hot shoe and converts the camera's TTL signal to a light signal. Fiber optic cables send this information to the strobe. The device allows you to switch between TTL and manual flash exposure control. It also allows you to use fiber optic cables with cameras that do not have a built-in flash.
The Olympus UFL-3 underwater flash also supports TTL through the fiber optic cable. This flash has a remote control mode that allows you to control the strobe’s power from the back of certain Olympus cameras.
Rebreather diver on Japanese shipwreck
The Fantasea Line Cool Flash Nano has 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.
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 hasn’t recycled.
Wide-angle lenses allow you to get close to large subjects.
Recycle times are given by manufacturers to reflect the time you must wait until the strobe can be fired at full power. When shooting at a close distance in TTL mode or when turning down the power, the strobe may 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 DS160, DS161 and Sea & Sea YS-250 use a special rechargeable battery pack. For example, the DS160 recycles in only 1.4 seconds after a full-power discharge, and it will fire approximately 450 times at full power on one charge. The disadvantage of this kind of battery is that you need to carry along expensive backup batteries. In comparison, the Sea & Sea YS-01 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 batteries, the strobe will recycle in only 1.9 seconds and you will get 330 pops at full power. If you're on an expedition where it is impossible to recharge batteries, you are better off with a strobe that uses AA battery power.
Built-in Continuous Light
Some strobes have a built-in continuous light to be used as an aiming light or for capturing video. This light source, in the middle of the flash tube, 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 help solve this problem.
Ikelite DS161 strobe
The Ikelite DS161 has an LED light that is bright and wide enough for video capture. This 5W LED produces 500 lumens of light and has a 45-degree beam angle. The 5000K color temperature is about the same as daylight. When used as an aiming light, the LED goes out for a moment when the strobe fires. This way, it does not affect the image if you are shooting with a slow shutter speed.
North Carolina Sand Tiger shark on the wreck of the Papoose
The Ikelite DS-160, Sea & Sea YS-D1 and YS-01 have an LED aiming light. These aiming lights also go out for a moment when the strobe fires. Another benefit of aiming lights is that they will also help your autofocus camera work in low-light environments.
Arms and Camera Trays
Once you've decided on the best strobes based on the features you need, you must be able to position them correctly. To achieve this, you must attach the strobe to an arm and attach the arm to your housing or a grip handle on your housing's tray.
Using strobes is necessary when shooting inside wrecks.
There are a few different kinds of light arms. Ball-joint and flex arms are the most popular. Ball-joint arm sets have two or more segments, with each segment featuring a ball at 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. Beneath the Surface, Aquatica’s TLC, Ikelite, and Sea & Sea, are among the most popular brands of ball joint arms at B&H.
Flex arms consist of a group of interlocking sections that can be moved into different positions. Beneath the Surface, Ikelite, and Fantasea Line are a few of the many companies that produce flex arms.
Flex arms are economical and easier to use. They are very popular for video lights. It is possible for the interlocking sections to come apart while underwater, which is why Beneath the Surface places a stainless-steel cable inside their flex arms. This could prevent loss of your expensive strobe.
Ikelite quick-release handle
After you've chosen an arm set, you must mount the strobe arm on the housing. Most DSLR housings allow the light arm to mount on the housing or tray's grip handle. Ikelite housing handles use a quick-release system. It is possible to mount a ball directly to an Aquatica or Sea & Sea housing’s handle. You then attach the ball-joint arm with a ball clamp. Another option is to attach a dovetail base on top of the housing’s handles. The arms slide onto the dovetail and a set screw holds them in place.
Many housings, including those for small point-and-shoot cameras, have a tripod mount on the bottom. A tray can be attached to this point.
Reef scene in Bonaire
Whatever style of arm you choose, remember: its purpose is to position the light. The strobe arm should be an extension of your own arm, rigid yet flexible and responsive.
See the accompanying specifications table to compare features on the many strobes available. In our next article, we will go over continuous lighting for video, stills, and focus lights. 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 lights, you'll bring back amazingly colorful photographs that will astound your non-bubble-blowing friends!