Its a big wide world beneath the waves, but you wont be able to record it easily without the help of additional lenses. Mark Koekemoer explains
GLIDING TOWARDS ME, a gentle giant thrusts out its wings. I take aim. Almost colliding with me, the graceful beast swoops overhead. Panning, I take my shot.
An exhilarating experience - a disappointing image. On review, I notice that Ive clipped the manta rays wings. This was my first photographic opportunity with these majestic creatures.
Somewhere in our collections we all have images of divers, large marine life or even wrecks with bits chopped off. In other cases, we have been forced so far back to get the subject in frame that definition and colour are almost absent.
As underwater photographers, we are severely disadvantaged before we even press the shutter release. Sunlight is diffused as it travels through the atmosphere, even more so if it is a cloudy day.
Light is further reflected off the waters surface. What little penetrates the surface is then absorbed and scattered by particles in the water. This process, known as diffusion, reduces contrast.
So the golden rule is to get close - reduce the column of water between camera and subject.
This presents a problem with a big subject that wont fit in the frame. Weve all taken photos of a group of people topside, and backed off to get everyone in the shot, but we dont have that luxury under water. The solution Wide angle!
A wide-angle lens is one with a notably wide viewing angle, this being measured in degrees.
Youve probably seen compact cameras marketed on their wide-angle capabilities, given in millimetres - for example 35mm, 28mm or 25mm. Relating back to angle of view, these figures correspond to 62°, 74° and 84° respectively.
Now this might be a selling point for topside photographers, but it is in no way suitable for underwater wide-angle applications.
Why Because when the camera is in a housing with a flat port, the viewing angle of the lens is reduced. This is the result of refraction.
Lens solutions: Light travelling from one medium (air) to another (water) changes speed and so bends. The refractive index of water is 1.33, which means that a 28mm compact camera that can view 74° in air sees only 56° under water. There are two solutions.
The first is to use a dome port, a curved glass or acrylic attachment that can be pushed over the front of some housings. Its curvature counters refraction and allows the camera to see its original viewing angle. A 28mm compact with a dome port would have a viewing angle of 74° under water.
This is still not very wide, however. More effective is to attach a supplementary wide-angle lens to the front of the housing.
Containing various elements with magnifying properties, these wet lenses can be interchanged on a dive - giving divers with compacts a huge advantage over those using SLRs.
Angles: General wide-angle underwater lenses cover about 100°, while super-wide-angle lenses can cover 150°. There is even a lens that will cover 165° - the fish-eye.
Your choice depends on your subject matter and the conditions in which youll be diving.
If you are predominantly diving in waters with good, reliable visibility and little of interest in terms of big marine life or wrecks, you could probably get away with a general wide-angle lens. But if youre into big stuff, scenics, wrecks, or simply dive in poor-quality water, you probably need a super-wide-angle or fish-eye lens.
With the small size of the compact combined with the versatility afforded by supplementary wide-angle lenses, your set-up will fit into areas other bigger camera systems cant.
Close-ups: Wide-angle lenses can focus very close to the front of the lens, so lend themselves to a technique known as close-focus wide-angle.
Place the lens close to a primary subject in the foreground, while framing a secondary subject in the background. This creates a steepened perspective, which can be very effective.
An example would be composing a clump of tubular coral close to the lens and having a diver silhouetted against the sun in the background.
Shallows: Wide angle is great for taking advantage of shallow waters. Objects near the surface are reflected and can be captured in beautiful scenics, especially if the water is calm.
Coral gardens, grass beds and jetties are particularly good places to try out.
If your lens has a dome, you may want to try split-levels. Find an interesting underwater subject and a complementary topside view, and hold the lens half in and half out of the water.
Self-Portraits: These are another great way to take advantage of wide-angle. You can just turn the camera on yourself and fire, but you may want to consider a more creative approach than simply spitting your reg out and pulling a face.
Consider your surroundings; look to where the light is coming from. In the image of myself (left) I have used the sun to backlight the jellyfish, with a hint of flash to fill out my face, which would otherwise have been in shadow.
Composing was made much easier because I could see my reflection in the dome. I made an effort to direct my eyes to the jellyfish to create a connection for the viewer - staring into the lens does not create a pleasing effect.
Next month: How to approach a subject to maximise a successful photograph.