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David Fleetham is one of the most published underwater photographers in the world—and the only underwater photographer to have a photo on the cover of Life magazine. Ninety-nine percent of his strobe-lit images are taken using TTL
 

Strobe lighting is critical to enhancing color, contrast, and clarity in your underwater photos. But they add another variable to adjust in an already challenging environment. Often photographers who make an investment in strobes come back disappointed that their results are lackluster and wildly inconsistent. TTL can help with that.
 

What Is TTL?

Surface photographers on the move largely rely on TTL (“through-the-lens”) flash exposure, where the camera meters a scene and automatically adjusts flash output accordingly. Ideal flash output is basically a function of aperture and distance to the subject, making it a perfect choice for automation.

TTL is essential when the photographer and/or subject are moving and in low-light situations. It decreases the number of variables you need to adjust as conditions change, allowing you to more effectively manage settings like shutter speed, ISO, and aperture on the fly.
 

When a subject is quickly approaching you, it is difficult if not impossible to adjust your strobes in time

Why Aren’t You Using It?

So why do so many underwater photographers swear by manual flash exposure? The answer can partly be traced back to the dawn of digital cameras. When digital cameras became popular in the early 2000s, they introduced a new TTL flash protocol that was different from that used by film cameras. Underwater photography flash manufacturers raced to catch up with this new technology and develop interfaces that communicated effectively with these new protocols. Some never caught up. And in the meantime, many underwater photographers who had already made the move to digital were forced to adapt and use manual flash exposure techniques instead.

Even as TTL exposure for digital cameras became very accurate and access to it became widely available, these photographers had already gotten used to the new ways of using their digital cameras. It’s similar to commuters that are required to take a new route due to construction; many actually continue using the new route even after the road barriers have disappeared.

In many instances, the underwater photographers that stand by manual flash exposure are accomplished professional shooters that tend to dominate the flow of information on the subject—through articles, photo courses, and seminars. As a result, those beginning their underwater photography journey will typically be told that manually adjusting flash output is the “best” or the “only” way to shoot with strobes, while TTL is looked upon unfavorably or even ignored.
 

Wide-angle photography is a wonderful application of TTL flash exposure. Use your camera’s manual exposure mode and adjust your aperture, shutter speed, and ISO to balance the background. TTL flash will automatically set the strobe power to properly expose anything within the range of your flash

Not All TTL Methods Are Equal

There are two types of TTL exposure and they are not equally accurate. The traditional type entails direct communication between camera and flash, typically through an electrical connection (sync cord) but sometimes also through an optical connection (such as Olympus RC mode). This method can be highly accurate, largely because the camera knows that an external flash is in use and is properly metering the scene as a consequence.

A second method is often called “sTTL” and involves no electrical connection or special signaling mode from the camera. This method is based on mimicry, whereby the strobe monitors the camera’s flash and adjusts its output in ratios. This method often leads to inconsistency in exposures—particularly when the camera does not have enough light to meter the scene properly—and has unjustly tarnished the reputation of true TTL.

Thus, in the following, we are referring to the methods of traditional TTL, featuring a sync cord connection or using the camera’s wireless external flash mode.
 

Creative Control

Many shooters eschew TTL flash exposure, citing lack of creative control, without realizing that TTL is based on the same fundamentals we use for successful manual flash exposure. When using manual flash exposure, we typically set our flashes for an expected power level based on distance from subject and desired aperture—lower power for close subjects  and open apertures, and higher power for more distant subjects or small apertures. Then, exposure is tweaked as we shoot, a little up or a little down.

TTL is operating on exactly the same principles. The camera asks the flash to fire a quick “pre-flash,” one or more short bursts immediately before the main flash. The camera analyzes the amount of light that bounces off the subject and returns to the camera’s sensor—through the lens. The camera uses this information to set the base level for flash output. The photographer can execute a great amount of creative control using flash exposure compensation, generally a range of up to two f-stops higher or lower than the camera’s calculated base value.

The added benefit is that flash exposure compensation can be managed in camera in a simple menu setting, directly accessible from the housing, rather than reaching out and manipulating control dials on each strobe. 
 

Sandy bottom, bright background, and multiple subjects are no problem. This shot was taken with a Canon EOS R5 camera with electrical strobe connection and Ikelite DL5 TTL converter. The next image shows the photos captured by the photographer in the scene
 

Two photos taken within 30 seconds of each other by zooming the Olympus TG-6 camera with FCON-T02 fisheye conversion lens. The strobes were firing via optical TTL connection using Ikelite RC1 TTL receivers. Flash metering is perfect in both shots: The system is not confused by the change of the scene from ultra-wide circular fisheye to macro

Another Level of Accuracy

Underwater strobes generally have about 10–12 power settings available via their external control dial. In most cases, particularly when shooting macro, this simply isn’t enough. This conundrum has led some photographers to think they need large, powerful strobes for wide-angle photography and compact, lower-power strobes for macro.

TTL strobe exposure typically expands access to dozens—or even hundreds—of flash power levels. These power levels span a significantly larger range of exposures and can provide the perfect flash output for any scenario, from the widest wide-angle scene to the smallest macro subject.
 

Two photos taken on the same dive four seconds apart. The speed and increased number of fractional powers available in a quality TTL strobe system makes it easy to knock off a sequence like this

More Versatile Than You Think

Ask an underwater photographer whether they use TTL and they may give you a very specific list of situations where it “works” or “doesn’t work.” Perhaps it’s considered best only for wide scenes or only for macro subjects. Maybe they claim it never works in light colored or sandy environments. They’ll probably say it doesn’t work for highly reflective subjects like silversides.

One could argue that these are all misconceptions often based on negative personal experiences from decades-old technology, a lack of access to accurate TTL systems, or both. In reality, TTL can be used effectively in all of the scenarios listed above.

Moreover, TTL is essential for getting properly exposed photos when your subject is moving towards or around you quickly as can be the case with sharks, turtles, sea lions, and a host of other creatures we hope to encounter underwater.

If you aspire to take photographs that could grace the cover of National Geographic or any scuba magazine, then TTL is for you. David Fleetham has been shooting since the mid-1970s and is one of the most published underwater photographers on the planet. Asked about using TTL, he says, “I swear by the technology and have been using it ever since Ikelite figured it out. I would say 99% of my strobe-lit shots are all taken with TTL.”
 

Some people mistakenly believe that TTL will get confused by highly reflective subjects like tarpon or silversides

Don’t Get Stuck

We photographers are creative artists and we don’t want to get painted into a corner. We typically enter the water not knowing exactly what we will see or shoot.

Choosing a TTL strobe system is not an all-or-nothing venture. Upgrading to a TTL system generally does not prevent you from shooting with manual strobe exposure. Most TTL systems make it possible with the press of a button or toggling a camera menu setting. The best TTL systems also allow easy adjustment of the strobe intensity up or down through flash exposure compensation in camera.

The last and perhaps biggest misconception that is out there about TTL exposure is that you can only use it with one of the camera’s automatic exposure modes—like Program, Auto, Shutter Priority, or Aperture Priority. This was true for some cameras in the dawn of digital cameras, but it is not true today. The vast majority of successful underwater photographers shooting with TTL strobe exposure are using their cameras in the Manual (M) exposure mode and selecting their aperture, shutter speed, and ISO independently of their strobe setting.
 

Ikelite TTL converters are in line with the electrical sync cord and usable with a wide range of housing brands, including Nauticam and Aquatica. They allow you to switch between TTL and manual flash modes at the press of a button. They support in-camera flash exposure compensation as well as rear curtain sync, and don’t need batteries since they are powered by the strobe

How to Get Started

There is a TTL underwater strobe option available for just about every camera model on the market today. But not all strobe and housing manufacturers support direct TTL communication between the camera and a strobe.

Ikelite has a reputation for offering the widest range of accurate TTL exposure options for nearly every camera model and most popular housing manufacturers. Strobes from Ikelite, Olympus, AOI, and others are offering support for OM System/Olympus and Panasonic wireless TTL systems. And a few third-party manufacturers like Trt-Electronics and UW Technics also offer intermediary solutions.
 

Contact Ikelite or your most knowledgeable local underwater photography specialist to ask about TTL options for your camera model of choice.