TTL vs manual flash underwater

The latest series of underwater flash units are all equipped with TTL. But what is TTL? What does TTL vs manual flash do? And when do you use which mode? Do you even need it if you also know how to flash manually? Both methods have their pros and cons, depending on your experience, environment and creative goals.

What is TTL?

TTL (Through-The-Lens) refers to a technique in which the camera measures, through the lens, the amount of light reflected from the subject. This is done in conjunction with a pre-flash, with which the camera automatically adjusts the flash power. This corrects exposure and flash settings in real time, depending on the distance to the subject and surroundings.

• How does TTL work?
  1. The camera sends a preflash to the subject.
  2. The reflected light is measured via the camera's light sensor.
  3. Based on this measurement, the camera calculates the optimum flash power.
  4. The flash automatically adjusts the output.

What is manual flash?

With manual flash settings, you control the flash power, often expressed in fractions (e.g. 1/1 for full power or 1/16 for a softer flash). You fine-tune exposure by controlling flash strength, distance to the subject and position of the flash(s). This gives you more creative freedom, but as a result you need sufficient knowledge of the settings, what they do and how they affect each other. I personally prefer to set everything manually, both my camera and the flash. That way I know that the photo will get the effect I had in mind. Of course this sometimes goes wrong, especially in situations where speed is of the essence. So I always try to think ahead: What are the animals I might encounter? What lens do I have on the camera and what distance to the animal is realistic with that?

Advantages of TTL

• Speed and ease: Ideal for fast-paced action and dynamic environments where you don't have time to make manual adjustments.
• Automatic adjustments: TTL is useful in changing conditions, such as shooting moving animals or varying distances.
• Beginner-friendly: It simplifies the process, allowing you to focus more on composition and less on technical settings.

Disadvantages of TTL

• Limited control: TTL makes decisions based on light metering, which does not always match your creativity.
• Problems with contrast: In high-contrast situations, such as clear water, bright lights and shadows, TTL may struggle to meter accurately.
• Unpredictability: Reflections from sand, fish or other surfaces can confuse TTL.
• TTL is clever, but obviously doesn't really know what your photo vision is.

When is TTL useful?

• Moving subjects: Think of turtles, fish or other animals changing position unexpectedly. TTL keeps exposure consistent while you track your subject.
• Quick adjustments for varying distances: TTL instantly adjusts the flash power as the distance between you and the subject increases or decreases.
• During trips: For beginners or photographers with limited time underwater, TTL can be a godsend because you can get faster results without having to adjust many settings. That way, at least you come home with something. Then you can continue practising in the pool.

When does TTL work best?

• Macro and full-frame photography: TTL performs well for subjects close to the lens with a simple, consistent light environment.
• Open water without background: In situations without much visual contrast, such as blue water photos or blackwater diving, TTL can be efficient.
• Simple exposure: For example, in clear water with an even light pattern.

Flash compensation with TTL

Flash compensation is a useful tool in TTL flash. It allows you to manually correct flash power even if your camera calculates the base exposure. This is especially useful in situations where standard TTL metering is not perfect, such as reflective or very dark subjects.

Compensation is usually set via your camera's flash menu or directly on the flash itself. Positive values (+EV) add more light, while negative values (-EV) reduce light. Say you are photographing a silvery fish: the reflections can mislead the camera and result in an overly dark shot. By setting +0.5 or +1 EV flash compensation, you correct this. For a dark object in clear water, a -0.5 EV may be needed to avoid overexposure.
The disadvantage of compensating is that the light metering via TTL might be slightly different in the next photo. And you have to reset your compensation.
You may then wonder which setting you prefer to adjust: TTL vs manual flash.

The challenges of wide-angle photography with TTL

• Complex lighting situations: In wide-angle photos, you often use two flashes that need to be set separately. TTL can struggle to measure this complexity correctly.
• Contrast in the scene: Strong contrasts between shadow, clear water and sunlight mean that TTL cannot always deliver correct exposures.
• Creative choices: For highlighting a foreground or subject against a dark background, manual control is often better.

When to choose manual settings?

Complex situations: For wide-angle photography or challenging lighting conditions, manual flash offers more flexibility.

Creative control: Manual flash allows you to tailor the exposure exactly to your idea, for example when emphasising details or playing with light fall.

Consistency: Manual settings ensure that all photos in a series have the same exposure, which is useful for post-processing.

Not All Cameras and strobes Work Together with TTL

It is important to note that not every camera works seamlessly with every flash in TTL mode. While many flash units are compatible with various brands, restrictions or additional tools may be required.

For example: the Nikon Z8 cannot TTL flash directly with the Backscatter Hybrid Flash without an additional trigger. For me, this is no problem at all as I am used to manual flash. So before buying a flash, check the specifications and compatibility to avoid surprises underwater! 😊

Conclusion TTL vs manual flash

TTL and manual flash are both valuable tools, each with unique advantages and limitations. While TTL is ideal for speed and simplicity, manual flash gives you the freedom to fully use your creativity. In recent years, TTL flashes have been getting better and better in combination with a good number of cameras. Be sure to try out both modes and see at which moments you can achieve the most.
By using both techniques, you can combine the best of both worlds!