BIG HEAVY FLASHGUNS made in Germany used to be the order of the day when we shot pictures under water on film.
Three things have happened since then. Airlines now charge swingeing amounts for excess baggage; there has been a revolution in battery technology; and we have enjoyed the advent of digital cameras.
Modern digital cameras can operate in remarkably low light conditions, so one doesn’t need so much flash power to get a result.
I bought a camera that can almost take pictures in total darkness. Unfortunately this is not very useful under water, because the ambient light is always flat and from above, so the pictures do not look three-dimensional.
The colour of light only a few metres from the surface tends to be monochromatic too, so I still need to carry a source of white light.
To take nicely lit, full-colour wide-angle pictures in tropical conditions when the reef is flooded with bright daylight filtered blue by the water, you need a lot of localised white light to compete – just as you did with film.
So the challenge was to find a flashgun (or perhaps two) that would give plenty of oomph, yet be light to transport.
Sea & Sea almost had the underwater market to itself at one time.
More recently, it produced flashguns that put out as much light as the formerly state-of-the-art INON 240Z but were much bulkier.
Sea & Sea also made small flashguns, but these could not outperform their rival.
But now its designers have risen to this challenge and produced the YS-D1. They say it is the most versatile and highest-performing underwater flashgun they have ever made.

The Flashgun
The YS-D1 is powered by four AA rechargeable lithium-ion batteries that sit in a floodable chamber. By floodable, I mean that should you foul up with its O-ring, while inserting freshly charged cells, the whole flash won’t be toast.
An over-pressure valve takes care of any gases given off by the batteries.
Unlike the INON, which uses two small flash tubes, the YS-D1 has one large tube, which augurs well for longevity with repeated use over short periods.
My INON tubes have blackened with time and heavy use.
The YS-D1 has a switch for setting the appropriate on-position to match your camera’s, and it is easily operated with a heavily gloved hand. The same can be said for the output control opposite. It can be adjusted from a guide number (with ISO 100) from 1 to 32.
Manufacturers are always optimistic about light outputs. If you are comparing the YS-D1 to those seven products featured in our recent flashgun comparison, I would halve that top power to be realistic.
Nevertheless, a guide number of 22 is twice that we found with the INON 240Z and equals that of the more massive – by size, weight and price – Ikelite DS161 and Sea & Sea YS-250 Pro.
It is twice as bright, 50g lighter and 10% smaller than the YS-110 Alpha.
The modelling light is operated by a push-switch. How easy is that

The YS-D1 has three different TTL circuits: DS-TTL (II), slave TTL and conventional Nikonos-type circuitry.
The revised algorithms used in the DS-TTL system can adjust the interval between the camera’s pre-flash and primary flash to suit a variety of cameras. The YS-D1 enables a wide range of synchronised flash photography such as slave TTL and manual (with 11 settings) for both compact and SLR cameras.
In DS-TTL mode, there is still a method of exposure compensation of (+/-) four steps.
Besides being linked by a fibre-optic cable, the YS-D1 can also be linked via a hard-wired strobe cord and give TTL automation if connected to a Sea & Sea YS converter.
You could always use two YS-D1 flashes, one on auto TTL and one manual for creative lighting effects, or both on TTL auto as you wish. It can also be hard-wired to a suitable camera for manual use, a method favoured by most serious underwater photographers.
The YS-D1 comes with both a standard Sea & Sea mounting-arm connection and a standard 1-inch ball mount, so that we can all integrate with existing mounting arms.

Ready Light
The flash-ready light is big and bright. It shows green to confirm that it worked, or blue if used as a slave flash. It takes slightly less than two seconds to recycle after it has been fired when using ni-mh batteries, on par with its INON rival.
An automatic power-off function saves battery life. The YS-D1 gives an unprecedented 250 flashes with one set of ni-mh batteries.

In Use
To give plenty of angle of coverage, there is a choice of two thicknesses of diffuser that simply clip over the front of the unit. These cut down light output as well as spreading it wider.
With my super-wide fisheye lens, I still managed with the less diffusive one. It remained bright enough to photograph divers a couple of metres away, which with that lens meant I could photograph them lit up in a wide seascape.
In the past, I found the colour of the light put out by Sea & Sea flashguns a little cool, but at 5250°K with diffuser, this was not the case.
So my trial of the YS-D1 was a great success. I’m used to working with a pair of flashguns, but I quite liked the effect of a single light source balanced with the bright daylight, and the big flash tube gave a soft-enough light.
The only thing I couldn’t test was long-term reliability, but Sea & Sea has a good reputation.

INON 240Z, £685
Ikelite DS161, from £820

PRICE £555
GUIDE NO 32 (manufacturer’s figure)
POWER SOURCE 4 AA batteries
SYNCH CORD Fibre optic or five-pin/Nikonos
DIVER GUIDE width=100% width=100% width=100% width=100% width=100% width=100% width=100% width=100% width=100% width=100%