SO HOW DO YOU CHOOSE an underwater electronic flashgun Considerations include the maximum brightness of the flash, the breadth and evenness of its beam, the colour temperature and quality of its light, and the time it takes before the capacitors are ready to give another flash (important when photographing subjects that may not keep still).
Then there are the number of flashes per battery loading (important in this age of big memory cards and the possibility of shooting lots of pictures during a single dive) and the time it takes to recharge a unit between dives.
Of course, there are other considerations too, such as the overall weight of a unit and its reliability.

LIGHT OUTPUT
You will often hear the opinion expressed that digital cameras don’t need the power outputs of big flashguns to get good results. This may be misleading.
Cameras with bigger sensors can be used at higher sensitivity settings, but monochromatic colour and the flat top-lighting normally experienced at depth means that an independent light source will be needed.
Bigger sensors require more light to enable smaller lens apertures to be used.
At the same time, in the shallows the ancillary flashgun must compete with bright and usually monochromatic daylight, and for this reason a good output gives better colour rendition.
A good big’un can still beat a good littl’un.
We compared the brightness of each flashgun(without any diffuser fitted) at a distance of 1 metre, bearing in mind that at distances much greater than that, the colour-absorption effect of water on the light passing through it means that the colour quality of the light produced even by incredibly powerful flashguns will start to be affected.
As a guide, experienced underwater photographers know that their flashguns have an effective maximum range of only around 2m unless they are in the total darkness of a night dive, or inside a wreck or a cave without any natural light competing with the flash.
A diffuser will make the light output more even, and therefore the aiming of it less critical, but will cut the light down by at least half.
Purely for comparison to the figures supplied by the manufacturer, we provide an exposure guide number in metres for ISO 100 that we established in our own tests in air.
We were disagreeably surprised to find that, as a rule, the actual maximum light outputs from all the flashguns were much less than those claimed by any of the manufacturers’ guide numbers. We used an electronic flashmeter and also double-checked our readings by taking a digital photograph of the flashmeter at the setting it displayed.
Light output/power is based on comparative guide numbers. These numbers are derived from distance multiplied by the f/stop required to get the correct exposure.
This system accounts for the Inverse Square Law, whereby the light falling incident upon a subject is inversely proportionate to the square of the distance involved.
Guide numbers are therefore particular to one ISO setting and the distance in metres.
A different guide number is derived for an alternative ISO setting and if imperial measurements are made for distance, so they are useful only in a like-for-like comparison.
What we also discovered was that the most powerful of the flashguns tested was effectively only twice as bright as the least powerful.
The colour of the light is important too.
In our experience the nearer it is to 5500°K (the colour temperature of daylight on a sunny day with plenty of white clouds passing across the sky) the more satisfactory it is.
The miniaturisation of the electronics means that modern flashguns punch above their weight, but bear in mind that the amount of heat generated by tiny flash-tubes will affect their longevity, especially if you take advantage of fast recycling times.

WHAT’S AVAILABLE
If you wish to combine an ancillary flashgun with a digital compact camera, I would urge you to check for compatibility of automatic exposure control before you make your purchase.
Most manufacturers have this information available through their websites.
The good news is that you can sit at home and experiment to find the best synchronisation setting, because you get instant feedback from your camera’s LCD.
Once accustomed to using a single ancillary flashgun alongside your underwater camera, you’ll probably want to extend your creative horizons by adding a second. The best option is probably to buy one identical to the first.
It is important that they output the same colour of light and, although most can be slaved one from another by inbuilt photo-electric cells, it’s sometimes more reliable to daisy-chain them via a fibre-optic connection.
By doing this, another diver’s flash will not fire your own slave flash before you’re ready.
Some very low-power units used to be available but these seem to have fallen by the wayside, thanks to rising costs in the Far East.
As I write, the market for underwater flashguns for divers has consolidated into a choice of three major brands – Ikelite from the USA, and INON and Sea & Sea from Japan.
The distributors of each sent us examples of their most popular models, and we added the specifications for two others from Sea & Sea that are available to special order.

HOW FLASHGUNS WORK
Electronic flash can produce a pulse of light that is more intense than anything that can be emitted from a continuous light source.
It does this by charging up a capacitor from a power source such as a battery. Its release of energy through a tube filled with a rare gas provides a blinding flash that has to synchronise with the instant in which a camera grabs a shot.
In the case of small portable flashguns, the pulse of light can be very short indeed – as little as a thousandth of a second.
With cameras that have shutters built into the lens, the pulse must occur when the shutter is fully open.
With cameras that have a blind with a slit opening that passes across the focal plane in front of the sensor (DSLR and other caneras with interchangeable lenses), the pulse must be emitted only once the sensor is completely revealed.
The Far East’s electronic whizz-kids have designed digital cameras that can operate fully automatically even if used with a built-in flash.
The problem for underwater photographers is that the built-in flash is by definition too close to the lens axis, and will light up all the detritus in the water. We need to use an ancillary flash mounted some way off-centre. It’s synchronising this flash with modern electronic cameras that often proves to be the problem.
This is because to get a light measurement for automatic exposure control, many cameras emit a weak pre-flash moments before the actual flash goes off and the picture is taken. If the built-in flash is being used to tell the ancillary flash when to fire (via a fibre-optic connection) it might send the wrong signal, and the ancillary flash will fire when the camera’s shutter is not at the right phase of its action.
Through-the-lens exposure control is now variously described as eTTL, iTTL and so on.
At the same time, the electronics experts employed by flashgun designers come up with protocols such as DS-TTL (digital synch, through the lens) that are intended marry up their products with various cameras.
Every camera manufacturer uses its own electronic protocol, so choosing and operating a separate flash means reading each instruction manual closely, and experimenting a bit.
At least with a digital camera you get instant feedback of the results, but most expert underwater photographers using digital cameras have reverted to using manual settings.
The size of the lens opening combined with the duration of the shutter opening copes with the right exposure for the ambient light, while the size of the lens opening alone regulates the exposure made with the pulse of light from the flash.
Many flashguns can be controlled to reduce the amount of light they give out during a given pulse. This usually alters the duration of that pulse. For example, a big underwater flash that can give out an energy burst equivalent to 100 joules may have a duration of 1/500sec, but turn that down to 25 joules (one-quarter power) and its burst of light will be only 1/2000sec.


SEA & SEA YS-02 £225
Originally intended for use as a slave to another flash to give more creative lighting solutions, this little unit represents an inexpensive way to add an ancillary flashgun, for those divers prepared to learn how to use their cameras with manual settings.
The recycling time at first appeared to be much longer than that claimed by the manufacturer, but after using it quite a lot to allow the capacitors to build up their strength, it came good.
FEATURES
Exposure Control
Pre-Flash Cancel Mode
Auto Power-off Function
Guide No (Power Output)
Beam Angle without Diffuser
Power Supply
Number of Flashes
Recycle Time
Colour Temperature
Target Light
Slave Function
Depth Rating
Weight
Contact
SEA & SEA YS-02
10-step Manual
yes
yes
16
100° x 100°
4 AA (ni-mh preferred)
330
1.9sec
5600°K
no
yes
75m
500g
www.sea-sea.net
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IKELITE DS51 £350
This smart little unit outputs 50 joules of light energy and represents an economic way to add an ancillary flashgun.
The manufacturer claims that it will work automatically with any camera system. The light it emits is a little cooler than most of the other flashguns listed here, so perhaps it should not be used in conjunction with a flash of another make.
FEATURES
Exposure Control
Pre-Flash Cancel Mode
Auto Power-off Function
Guide No (Power Output)
Beam Angle without Diffuser
Power Supply
Number of Flashes
Recycle Time
Colour Temperature
Target Light
Slave Function
Depth Rating
Weight
Contact
IKELITE DS51
TTL, 6-step Manual
-
-
15
70° x 70°
4 AA (ni-mh preferred)
200 (with alkaline cells)
3.5sec
5700°K
no
no
90m
610g
www.ikelite.com
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SEA & SEA YS-01 £408
This is a useful little flashgun that pops quite a punch. Its switches are not that easy to operate with gloves or water-sodden fingers, but we have to say it was better than some of the others!
FEATURES
Exposure Control
Pre-Flash Cancel Mode
Auto Power-off Function
Guide No (Power Output)
Beam Angle without Diffuser
Power Supply
Number of Flashes
Recycle Time
Colour Temperature
Target Light
Slave Function
Depth Rating
Weight
Contact
SEA & SEA YS-01
DS-TTL, TTL, 10-step Manual
yes
yes
16
100° x 100°
4 AA (ni-mh preferred)
330
1.9sec
5600°K
LED
yes
75m
505g
www.sea-sea.net

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INON S2000 £435
We anticipate this new little flashgun becoming very popular. It has plenty of oomph and a quick recycling time ready for the next picture. The only thing that’s missing is a target light.
We found the switches a little fussy and hard to manipulate with a gloved hand, and the ready light is inconveniently placed at the front, where it is less apparent to an underwater photographer lining up for a second or third shot.
In terms of light output and speed, however, it keeps up with its more expensive siblings.
FEATURES
Exposure Control
Pre-Flash Cancel Mode
Auto Power-off Function
Guide No (Power Output)
Beam Angle without Diffuser
Power Supply
Number of Flashes
Recycle Time
Colour Temperature
Target Light
Slave Function
Depth Rating
Weight
Contact

INON S2000
S-TTL, Nikon TTL, 12-step Manual
-
11
105° x 95°

4 AA (ni-mh preferred)
570 (ni-mh)
1.5sec
5500°K
no
yes
100m
295g
www.inonuk.com

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INON D2000 £565
To all intents and purposes this unit looks very similar to its popular older brother the Z-240, and we expected its performance in terms of light output to be the same.
It has the same arrangement of two flashtubes positioned one perpendicular to the other, but in tests we found that it gave only half of the output of its more powerful stable-mate.
This probably accounts for the fact that the manufacturer claims a lot more flashes at full power from this unit from a fully charged set of batteries.
FEATURES
Exposure Control

Pre-Flash Cancel Mode
Auto Power-off Function
Guide No (Power Output)
Beam Angle without Diffuser
Power Supply
Number of Flashes
Recycle Time
Colour Temperature
Target Light
Slave Function
Depth Rating
Weight
Contact
INON D2000
S-TTL, Nikon TTL,
12-step Manual
-
-
11
100° x 100°
4 AA (ni-mh preferred)
420
1.8sec
5500°K
yes
yes
100m
600g
www.inonuk.com
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INON Z-240 £685
This is the unit that took the underwater photography world by storm. Its miniaturised electronics and consequent light weight arrived at a time when the competition used bigger flashtubes and heavy batteries.
The Z-240 employs two tiny flashtubes arranged one perpendicular to the other, to give an even cone of light. Recycling time is quick, and although the light output might not seem much, when you take into consideration the close proximity of subjects when shooting extreme wide-angle or macro, it’s enough.
The target light can be set to automatically extinguish just before the flash fires and re-light when the flash is recycled, so that the photographer is constantly in touch with what’s going on flash-wise.

FEATURES
Exposure Control

Pre-Flash Cancel Mode
Auto Power-off Function
Guide No (Power Output)
Beam Angle without Diffuser
Power Supply
Number of Flashes
Recycle Time
Colour Temperature
Target Light
Slave Function
Depth Rating
Weight
Contact

INON Z-240
S-TTL, Nikon TTL, Auto (24-step),
12-step Manual
-
-
16
100° x 100°

4 AA (ni-mh preferred)
240
1.5sec
5500°K
yes (camera shutter linked)
yes
100m
765g
www.inonuk.com

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IKELITE DS161 from £820
The DS161 represents an old-fashioned approach to underwater flashgun design, in that it is quite bulky thanks to a large rechargeable battery.
It’s a powerful unit of 160 joules max output (more than three times that of its little brother the DS51), with a large long-lasting flashtube.
Ikelite has chosen a different route to accommodate changing times. With more and more digital cameras able to shoot video clips as well as stills, this one can also act as a powerful video light.
An interesting feature is the battery state-of-charge indicator and the fact that it includes a recycling vibrator that gives an audible clue as to when it’s ready for the next shot. The colour of the flash light is attractively warm.
FEATURES
Exposure Control

Pre-Flash Cancel Mode
Auto Power-off Function
Guide No (Power Output)
Beam Angle without Diffuser
Power Supply
Number of Flashes
Recycle Time
Colour Temperature
Target Light
Slave Function
Depth Rating
Weight
Contact
IKELITE DS161
TTL, Adjustable in 10 steps
from 50% to Full Power
-
-
22
90° x 90°
Rechargeable ni-mh
225
1.5sec
4800°K
500 lumen video light
no
90m
1300g
www.ikelite.com
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AVAILABLE ONLY ON SPECIAL ORDER – BUT WORTH TAKING INTO ACCOUNT

SEA & SEA YS-250 PRO £900
This is the professional’s choice, assuming that someone else is paying the excess-baggage charges. It pushes out a lot of light and is rapidly ready for the next picture.
Unfortunately, we couldn’t get hold of a YS-250 Pro for this comparison test, because again it seems that the importer gets them only to special order. We would have liked to establish our own comparative guide number.
FEATURES
Exposure Control
Pre-Flash Cancel Mode
Auto Power-off Function
Guide No (Power Output)
Beam Angle without Diffuser
Power Supply
Number of Flashes
Recycle Time
Colour Temperature
Target Light
Slave Function
Depth Rating
Weight
Contact
SEA & SEA YS-250 PRO
TTL, 12-step Manual
yes
yes
32 (manufacturer’s figure)
105° x 105°
Rechargeable ni-mh
200
1.8sec
5600°K
yes
yes
60m
1780g
www.sea-sea.net
 

SEA & SEA YS-110A £430
What a pity no-one, including the importer had one of these powerful flashguns available for our comparison test.
It represents what appears to be an extremely viable alternative to some others on the market.
The manufacturer’s guide number is the same as that for the INON Z-240, so we anticipate that it would have had a similar maximum light output.
FEATURES
Exposure Control

Pre-Flash Cancel Mode
Auto Power-off Function
Guide No (Power Output)
Beam Angle without Diffuser
Power Supply
Number of Flashes
Recycle Time
Colour Temperature
Target Light
Slave Function
Depth Rating
Weight
Contact
SEA & SEA YS-110A
DS-TTL, TTL,
13-step Manual
yes
yes
22 (manufacturer’s figure)
100° x 100°
4 AA (ni-mh preferred)
330
1.9sec
5400°K
yes
yes
60m
700g
www.sea-sea.net
 

Our thanks to Cameras Underwater, Sea & Sea and INON UK for supplying us with the necessary fibre-optic connections to enable us to fire all these different flashguns as slaves from our own occluded flashgun, which was synchronised to our camera.