THERE ARE CERTAIN FUNDAMENTALS THAT MUST BE OBSERVED BY A SUCCESSFUL PHOTOGRAPHER, and one of these is to use the right flashgun with your underwater camera.
Most importantly, it needs to be buoyant and perfectly balanced. Its no good having positive buoyancy at one end and negative at the other.
Most cameras are perfectly buoyant and balanced, but you'll benefit from this quality only if your flash has characteristics to match.
Follow this simple rule and a photographer is assured of being able to work in any position and situation, and wont be exhausted after hovering for 10 minutes while waiting to get that exclusive shot.
Another important factor is the size of the unit. Yes, size does matter, and here the rule is: the less the better. To light wide-angle shots, the flash is positioned far to the side, using long extension arms, and because of their water resistance huge light cannons become a major drag in such situations.
Many people overestimate the importance of power and output (as per guide number). In wide-angle photography, which is usually mixed-light photography, a guide number of 8 is quite sufficient. For extreme close-up and macro photography, however, things can get rather tight unless the subject is sitting out in the well-lit open.
And while a lot of power is required for macro, you generally achieve better colour reproduction using two small strobes at a colour temperature of 5600K.
It would be silly not to use automatic TTL exposure control for macro, close-up or for lenses covering angles up to 60. For larger angles, especially using super-wide-angle lenses, flash exposure is influenced by a number of factors and TTL exposure would not be appropriate.
This is easily understood when we look at how TTL exposure control works. Light emitted by the flash is reflected by the subject and measured by a sensor mounted in the camera, in front of the film plane. The sensor has been programmed to know how much light the film needs to be accurately exposed, and it controls exposure by limiting the duration of the flash.
This works well when the subject is well-defined in space and distance, as is usually the case when working close to medium range.
When working with a wide-angle lens, however, we have a different situation. Other than our main subject, there will be a lot of other stuff in the frame. The exposure program cant tell whether the light it measures is being reflected off the central feature or off something in the frame that is unimportant but closer to the camera.
Subsequent exposure errors are common. So for wide-angle photography it is advisable to go for manual exposure and take existing light into consideration.
Photographers often forget that thanks to that great big diving light in the sky they have daylight at their disposal as well. We use it to show more in our pictures than the flash alone can illuminate, but for optimum effect we mix the two light-sources, highlighting elements in the foreground by emphasising their colours by flash while available light generates depth in the background.
To achieve consistent results, apply Amslers Formula: AS + EA (aperture as per strobe + exposure time as per available light).
Any flash, whether of the dry or wet variety, prescribes a lens aperture. Theres nothing we can change about that, so exposure control for elements not illuminated by the flash has to be achieved by varying the time the shutter stays open.
For this purpose, the photographer needs to measure available (day)light, which is not a problem using the cameras built-in meter. Some housings even allow the photographer to switch from spot to integral or matrix metering!
To enhance contrast we aim for slightly darker backgrounds, so dont point the camera directly at the main subject but aim high - approximately 30 high towards the surface.
For instance, if the light meter shows 1/30sec for the flash aperture f8, then thats the exposure time we set on the camera. The slow shutter speed allows available light to expose parts of the film representing the background, and gives us the rich, dark, bluewater background were chasing.
After some practice with a light meter, the photographer will develop the ability to read the available light situation and be capable of working out the correct mixed-light exposure time from experience - for any depth or situation.
TTL exposure control systems are usually foolproof, but if you consistently bring incorrectly exposed films to the surface there has to be a reason, and we have to find it.
TTL systems can be adversely affected by contaminated contacts, resulting from connector use and maintenance. To avoid this, unplug connectors slowly, and wriggle as you pull. This avoids creation of a vacuum that can suck in droplets and contaminate the contact surfaces.
It is also important to apply the protector caps immediately, and to grease O-rings with the utmost care. Flash contacts can be contaminated only too easily, and this will upset the delicate currents involved in TTL metering. Unfortunately, the photographer is usually blissfully unaware of the situation because the flash still goes off - only without TTL metering applied.
Much better to be safe than sorry, so spare the two minutes required and execute the TTL test whenever contacts between flash and camera housing have been interfered with.
Proceed as follows: Assemble the camera and flash units, and for Nikon cameras advance film to counter 1. Set the flash to TTL, keep an eye on the ready light and flash directly at the lens.
As the flash will discharge only a minimum amount of light directly at the sensor, the ready light should either stay on or come back on almost instantaneously. If this is the case, you can trust that the electronics are working perfectly!
Should the flash take as long to recharge as it does in manual mode, however, there must be a problem somewhere. Your first step - and in 90% of all cases the right one - is to clean the contacts with ethanol!
SPECIAL FX: Flashguns are among the best tools for creating unusual effects. In this cave-diving image the main flash is detached from the camera on a long cable and held by the first diver. The second diver is holding a slave strobe to light up the cave in front of him.
LOW AND EASY: Visibility only 5 metres For getting clear pictures even in murky water, the flash or flashes have to be fired on very low power. This is also the time to consider mounting a diffuser to help avoid backscatter of particles in your pictures
IMPROVING ON NATURE: The bright colours of this Mediterranean gorgonian against the blue water are not real but the result of flash technique. Such reinforcement of natural colour can be achieved easily enough by using the desired filter in front of your flash
CONSTRUCTIVE SLAVERY: A slave strobe is great for achieving the sort of effects that make your pictures stand out from others. The slave can be placed among wide-angle scenery, or held by your buddy or model like a torch
one The priority is that the flash needs to be buoyant and perfectly balanced so that you can work in any position. A buoyant flash is easy to aim at the subject because it can be moved in any direction without releasing the joints of the strobe arms.
two Remember that in wide-angle photography the position of the flash is very important to avoid backscatter and to gain equal illumination. The larger the picture angle, the further the flash should be from the lens.
three TTL is a great invention, but while macro and close-up photography is no problem, using TTL for wide-angle is tricky, as any foreground or an incorrect flash position can result in under- or over-exposed pictures. Use manual flash mode for wide-angle.
four Because of refraction, all subjects under water appear closer. Never aim your flash at that apparent distance, because too much light will hit the foreground and the water between camera and subject, resulting in diffused pictures, overexposed foregrounds and back scatter. Aim the flash above the subject, or next to it if using two flashes. The ideal is to have a target light built-in or fixed on each flash.
five Take care of your flash connectors. Unplug them after a days diving and clean the tiny O-rings. Unplug them in such a way that no salt water drops onto the connectors. No grease should touch the pins, which should be cleaned regularly with alcohol.
six Always take a spare sync-cable on diving holidays. Many modern flashes use regular batteries but I recommend researchable batteries of 1500ma, as they recharge the capacitor much faster. In case of current problems on a diveboat, bring a pack of regular batteries too.
seven Using full-power flash in murky water has the same effect as using main beam when driving in fog! Thats because of all the dense particles, so the murkier the water, the lower the power you need. Reducing power is possible only in manual mode.
eight Ever wondered about the white diffuser cap most manufacturers deliver with the flash unit It makes the light softer and warmer and swallows one f-stop of light. Use it in murky water to reduce backscatter, and also if you take pictures of people in indoor pools or close-up. The skin tone will appear warmer.
nine Never forget to use ambient light as well as your flash! Mixing the two light sources is a must with wide-angle, to show more than the flash alone can illuminate.
ten Because of the distance light has to travel through water, the colour temperature of the flash plays a big role in reproducing accurately the original colours of your subject. Macro flashes of 5600K cannot be used for wide-angle because the light is too cold, while wide-angle flashes of 4900-5200K are too warm for macro. To modify your wide-angle flash for macro photography, use a light-blue foil on the flash.