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14, Mar, 2012

Using a strobe for underwater photography will, without a doubt, help to improve the quality and colour of your underwater images. But strobes can be tricky to get the hang of. Even using a strobe for basic shot types can be challenging, never mind when you are trying to create certain specific lighting effects.

So how do you know when to use a strobe and how to achieve the best positioning?


Deciding when to use a strobe

First you need to decide when to use your strobe. If you’re diving in clear shallow water, no deeper than around 8 meters, and the sun is shining, then it’s best to switch off your flash and use the sun to highlight your subject. In conditions like this, your strobe will not really be effective anyway, so try using the camera’s manual white balance menu to get help get rid of the green and bring back the true colours.

Strobe Techniques Shallow WaterThis picture of the Barracuda is a great example of turning off the flash and using the natural light to highlight your subject. Also with this particular subject, due to their shiny scales, a strobe could overexpose parts of the Barracuda’s bodies.

Once you start to go a bit deeper, or the conditions are darker then you need to start using a flash to counter-act the green and make the rich beautiful colours jump out at you. This is because water, being much denser than air, soaks up light like a sponge. This causes extreme loss of color and contrast at any significant depth. The longer wavelengths of sunlight, which are the reds, oranges and yellows, are absorbed quickly by the surrounding water and because of this everything appears blue-green in color, even to the naked eye .

The loss of colour not only increases vertically through the water column, but also horizontally, so subjects further away from the camera will also appear colorless and indistinct. This effect is true even in clear shallow water such as that found around tropical coral reefs. The only way to bring back the colours that have been absorbed is to use a flash.

Most cameras have built-in flashes, but unless you are very close to your subject, these are usually fairly ineffective due to their weak flash output. Moving closer will definitely help, but being close enough that your flash will light the subject adequately can cause a problem of it’s own – the lens port on many housings can obstruct the flash beam, creating shading across a portion of the picture. Not ideal when you want the whole of your image to be lit up.

Strobe Techniques Single StrobeTo help over come these problems, photographers use external strobes with their cameras. Basically an external strobe is a very powerful flash which is attached to the outside of underwater housings which can be moved into different positions depending on the effect you wish to create.

There are a huge array of strobes on the market from small basic manual ones, up to larger more powerful ones that can be synced with your cameras flash. When selecting an external strobe, choose one that is specific for digital cameras with automatic and manual settings and make sure it is compatible with your camera and housing. Having flexible arms which attach your strobe to your camera are a must, as these allow you to move the strobe around to where you want it to be. Try to get one which has a good power output and also check the recycle time after a ‘full dump’ of power. It can be very irritating missing a shot and watching your subject disappear into the blue, just because you’re waiting for your strobe to recharge. Using rechargeable nickel-metal hydride batteries will often give a shorter recycle time than normal single use batteries, and are better for the environment too!

Strobe Techniques Double Strobe Set-UpSome divers use one strobe for their set up and find this to be adequate, others prefer to have 2, one on each side of the camera.

The problem with a single strobe is that it can create a shadow on one side of your subject due to the light generally only coming from one side.

To try and reduce this effect, you can try to use natural light to illuminate your subject and use the strobe to fill in any dark areas. If this is not adequate for you, then maybe you should consider having a 2 strobe set up.


Deciding how to position your strobes

So where do you position your strobe in relation to your camera and subject? Well it all depends on the type of shot you are taking.

For wide angle shots, you want to have your strobes out and away from your camera as this will light up a larger area. If you only have one strobe, position it above your housing at a 45 degree angle and pointing towards the subject. For those with 2 strobes, if they are both of equal power then have one on either side of the camera, aimed straight ahead.

Some people have 2 strobes with unequal power. The main strobe acts as the sun (or main light source), while the other is a filler for extra light. When this is the case, for wide angle shots the main strobe should be positioned similar to that of a single strobe, and the filler should be at the other side at a lower angle to get the right balance of light.

When planning macro shots, your strobes need to be in a different position. Apart from your subject being smaller, the area you are photographing in will possibly be smaller too, so you will need to pull your strobe arms in closer to your housing. If you are using 2 strobes, then they can be pulled level with the lens port and angled towards the subject to get even lighting. To try something a bit different, try positioning the strobes to the side and slightly behind the subject if you have room. This can give a nice effect of side and back lighting, causing the subject to have a slight glow.

If you only have one strobe, try positioning it above the subject for some good results which give a nice effect with a sense of depth.

Strobe Techniques BackscatterStrobe Techniques Backscatter 2Try to avoid pointing your strobe directly at your subject (similar to the position of the cameras internal flash) as this can cause backscatter. By positioning the strobe at an angle, you can reduce the amount of particles which are lit up by the flash.

You can see from the diagrams that the image on the left is using the camera’s built in flash and highlights a much larger amount of water in front of the lens, meaning that more particles will be lit up. The image on the right shows how positioning the strobe will still light up the subject but less of the water between the camera and subject.

Strobe Techniques BackscatterBackscatter occurs when there are lots of particles in the water, such as plankton or silt, which get lit up by the flash/strobe and can ruin your picture. It is a particularly irritating phenomenon but can often be avoided by proper positioning and adjusting the output of external lights. Sometimes however, the conditions can just be so bad that it doesn’t matter what you do, the particles will still show up. In this case, you’re probably better off sticking to macro photography rather than wide angle, and shots which don’t have any water in the negative space.

You can see from the picture to the left that there is backscatter covering the photograph, effectively ruining what would have been a nice photo. To avoid this, the photographer could adjust the angle of the strobe so that just the edge of the beam is lighting the subject, and the intensity of the flash could be turned down.

Experimenting with strobe positions can really add a different dynamic to your pictures and can be fun too. Try to practice on one subject to see how different the picture can look. For example pick a subject then photograph it 3 times with side-lighting, back-lighting and front-lighting to see the different effects you can achieve. You could surprise yourself at just how different you can make your pictures look!

For more useful digital underwater photography techniques to help you get the most out of your underwater camera system, take a look at our Tips and Tricks section and learn about other types of underwater shots.

If you’d like to learn more about underwater photography, take a look at the Liquid Lense range of underwater photography courses. All Liquid Lense courses have been designed in-house to help you get the most out of an underwater camera system.

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