PhotoPro: Capturing the Rays

Photo:Alex Mustard

Ever since digital sensors took over from slide film as the preferred method for capturing pictures beneath the waves, one thorn remains wedged firmly in the new format’s side: sunbursts. Digital sensors just do not capture them with the same subtlety as film. This is an important failing because there are few elements that we can include in our photos that capture the ambience of being underwater better than shafts of light spearing down from the surface.

The root of the problem is that slide film was naturally predisposed to dealing with excessive highlights, which is what a sunburst is. Digital sensors have a more linear response to different intensities of light, and once it gets too bright, no data can be recorded and detail is lost or clipped. As an analogy, we can think of film as having more elasticity in its response to light. As more and more light hits film, it stretches and copes with the exposure. A digital sensor has a less elastic response, and once the light levels get too high, it is overwhelmed and it snaps.

Sunbursts on digital can be ghastly: an ugly white blob where the sun should be, encircled by a garish bright turquoise halo and no distinct, dancing rays. The solution of many underwater photographers is simply to not include the sun in their pictures any more. But why deprive our photos of this most attractive and characteristically aquatic light? Digital sensors can capture all the beauty of underwater sunbursts, but because they are not as forgiving as film, it is imperative to stick to the rules.

Most of the problems of capturing sunbursts on digital come from the sensor being exposed to more light than its dynamic range can cope with. The solution is to underexpose. The more we underexpose, the smaller the white ‘sunball’ and the unattractive turquoise halo around it become. However, the greater the underexposure, the darker we turn the water, and if we go too far we will deprive our photo of an attractive blue water colour to set the sunburst against. The right settings are a compromise between maintaining the water colour and controlling the size of the sunburst.

The best way to achieve this underexposure is to increase the shutter speed. If we change the aperture, we also need to adjust our flash power. Faster shutter speeds are also beneficial because they help to freeze the beams of light coming down from the surface, making them stand out more sharply against the water.

SLR cameras have a maximum shutter speed at which they can synchronise with our flashes – for most, this is between 1/200th and 1/250th of a second. If you have reached this limit and still need more underexposure to get the shot you want, you have to close the aperture and consequently increase your flash power to maintain a correct foreground exposure. In bright conditions, your strobes might not be powerful enough to enable enough underexposure of the sun.

Compact cameras do not have mechanical shutters and will synchronise with a flash at any speed, which makes underexposure much more simple. There is a maximum limit: above 1/1000th of a second, we will start to see a dropoff in strobe power because the exposure is not long enough for the strobe to discharge completely.

Certain environmental conditions are crucial for capturing good sunbursts. The most sharply focused rays are formed on windless days, when the smooth surface refracts the sun into clearly defined beams. Time of day is also important: the exposure for a sunburst is much more easily handled early or late in the day.

Similarly, we might expect that going deeper will help, but it does not because it introduces another effect: the sun’s light becomes increasingly blue, meaning that sunburst clipping tends to occur in the blue channel, but not in the others. This is the cause of the unattractive cyan/turquoise halo around the sunburst. The shallower we photograph the sun, the less pronounced this cyan halo is. The other advantage of staying shallow for sunbursts is that sunlight is often at its most beautiful close to the surface.

Perhaps the most valuable tool for helping our digital sensors to catch the rays is composition. Framing the scene so that the sunball is just outside the frame makes it much easier to expose the rays. Alternatively, obscure the sunball behind something in the picture, allowing the rays to spill out from behind. The dive boat is often conveniently placed to do this, or you can use the main subject itself.

Finally, technology helps too, and newer digital cameras are becoming better at handling sunbursts as their capability of recording more dynamic range improves. I took this photo of a great white shark with a Nikon D3, which, like many of the latest generation of digital SLRs, incorporates specification advances that improve dynamic range. Two factors are important: improved analogue-to-digital conversion and larger pixels. To go back to the analogy I used earlier, both help the sensors to be more elastic in their response to excess light. These are also one of the major advantages of a DSLR over a compact; to put it in perspective, each pixel on the sensor of the D3 is about 25 times the size of those on Canon’s G10, one of the best compacts around. I am not saying you must have the latest and greatest model (I had to return the D3 to its owner after this shoot), but it is important to be aware of the capabilities that new technology brings.

The lesson here is that sumptuous sunbursts are perfectly possible with digital. The key is to stick to the rules. Wait for calm conditions and shoot early or late in the day; underexpose, but not too much; use a fast shutter speed; stay shallow; and hide the sun behind the subject or just out of the frame. With a bit of care, digital can capture all the atmosphere and beauty of the underwater sunburst.

IMAGE DATA

Great white shark and sunburst, Guadalupe Island, Mexico. Nikon D3 SLR. Subal housing. Sigma 15mm fisheye. 1/100th at f8. 2 x Inon Z240 strobes with Lee warming filters