Electronics for Underwater Photography Flash

Written by Grega Bernot on April 16, 2018

We developed electronics for the underwater photographer's ultimate tool for unleashing creativity.

Diving into this project

This time, we were approached by a customer with a very concise and ambitious vision - to develop and produce a state-of-the-art strobe for underwater photography. The newly developed product would need to include a xenon flash tube and storage capacitors able to provide 100 Joules of energy, powered from only 4 or 8 AA batteries. The strobe would have to provide different ways of triggering, either electrically via cable, optically via fibre, or simply from ambient light. The strobe would have to provide exact setting of the flash intensity.

Our customer made our job easier by providing us with complete housing design and PCB placements. Nevertheless, development of this simple device proved to be everything but simple. For instance, one of many project requirements was to achieve as fast as possible capacitor recharging times. Namely, after discharing each capacitor needs some time to rebuild its initial voltage in order to be ready for the next flash. Designing an optimal solution was quite a challenge.

How hard can it be to develop a photographic flash?


Well, not that hard but when you look at the requirements, some pretty alarming numbers are lurking out. Charging a huge capacitor bank in almost no time? That requires huge charging currents! Moving a trunk of stored energy into a xenon flash lamp? This becomes a really difficult task to accomplish. We are dealing with energy that can easily compare to a defibrillator! If energy like that can bring a person to life it can as well kill you.

With that in mind, we were taking extreme safety precautions when developing and testing throughout the whole project's course. To be honest, there were a few "whoops" moments but luckily we got away with just a few burnt cables and transistors.

Let's do the math

We have high energy, high current and high voltage on one side, and then we also need to have very precise and sensitive detecting circuit on the other side. The detecting circuit should be triggered by either flashes via optical circuit or electrical pulses via electrical circuit. This is where our know-how from previous projects came in handy. But as all other things, nothing is as simple as it seems on the first sight - the triggering system also proved to be a tough cookie. We had to design a circuit that could detect flash with a lot of ambient light, and it should also detect weak light pulses accurately over optical fiber.


TTL FTW!


Optical triggering or the so called TTL (i.e. through the lens metering) mode is an advanced metering mode for calculating exposure time of a photo. When using TTL mode, camera uses pre-flashes before taking the photo. Such pre-flashes are usually really short which makes detecting them precisely a tedious task.

Our strobe also has to respond quickly to these pre-flashes. Otherwise, the camera may get confused and we end up with a useless photo. To make everything work correctly, we had to forget prewritten libraries in firmware programming and dive even deeper, namely to the lowest level and directly change some registers. This allowed us to save quite a few valuable microseconds. And to make things even harder, there is almost as many variations of TTL protocols as there is cameras on the market!

Feeling stressed? We sure did.


Another important part of the project was stress testing. The strobe is really powerful so there is a lot of energy in form of heat released when flash triggers at full power. We had to make sure that continuous triggering at full power wouldn't burn up the flash. We made a test bench for testing the strobe so we were able to set and change flash triggering times, output power and some other parameters.

Main subject of test monitoring was strobe temperature, working temperature of the strobe, charging time, battery voltages and total number of flashes made. Having a customisable and reliable test bench enabled us to make multiple different tests to verify that this strobe is ready for real world adventures.

You can see some of these adventures yourself as all these photos have been taken by the help of the developed underwater flash:

All photos originate from Mr. Alex Mustard's facebook profile and are his property. MULTILUX does not hold any rights to these materials. Feel free to visit his website for more amazing underwater photos!

The whole project is a synonym for tight cooperation with our customer. We managed to find dedication and passion for a successful end-product which results in a sexy looking, powerful and very intuitive underwater strobe. It has already been in hands of many divers all over the world providing us with wonderful pictures of underwater creatures.

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