There are some basic rules to getting clear sharp pictures, whether it be video or stills, while under water because it is the water that ruins so many good photographic opportunities. Firstly, the clearest water is not clear. Well, it’s not as clear as clear air might be. If you could eliminate the water, think how much clearer your pictures would be!
How do we do that? Simply by getting as close to your subject as possible and thereby eliminating as much water as you can between your camera’s lens and your subject. That’s why inexperienced underwater photographers have most success initially photographing macro subjects. Because they are small, it’s easy to get the camera up close and personal to them. You only need to enable the camera to focus on them. Those with top-of-the-range DSLR cameras can equip themselves with a macro lens specifically designed to focus very closely. The lens merely needs to be installed behind a flat lens port or ‘macro port’. Those with cameras that have a fixed lens (such as most compact cameras) will need to fit and auxiliary macro lens to the outside of their housing. The same can be said for GoPro POV cameras.
But what about bigger subjects? That’s where a wide-angle lens comes into play. Again, a DSLR user will need to fit such a lens and mount it on the camera behind a suitable dome port. Dome ports produce a virtual image just ahead of the camera so you must be sure your choice of lens will focus close enough on that. The advantage is that a dome port keeps the angle-of-view the same for the lens as it would be if used in air. Wide-angle lenses are not used to ‘get more in’ but to allow the photographer to move closer without ‘cutting more out’.
Again, compact camera users will need to fit an auxiliary wide-angle lens to the outside of their housing. There is a variety of choices but you should be advised by an expert as to which will suit the fixed lens of your camera if it is not to vignette the photographs. The advantage of fitting lenses to the outside of the housing is that these wet lenses, whether macro or wide-angle, can be interchanged at will, whilst submerged.
Water has another property that makes the life of an underwater photographer a little complex. It absorbs light so that as you go deeper it gets darker, but it also absorbs light selectively. The longer wavelengths of light (red and green) get soaked up first so that very soon, at a depth of no more than a few metres, everything will look blue in your pictures. What can you do about that
One way to look at it is to see it as a surplus of blue light and if you can reduce the amount of blue light you will allow the camera to make the most of the red and green light that still penetrates the water to the depth you are at. Some cameras allow you to ‘White-balance’ and provided the software designer has provided enough range to account for the excess of blue light, this can be very effective. It’s best to point your camera at something neutrally grey to do this. A piece of white Perspex is ideal but failing that, the palm of your hand underwater can usually be good enough. Canon compacts are especially good at white-balancing against an excess of blue. Sadly for underwater photographers most software designers are thinking in terms of white-balancing against incandescent light, which tends to have an excess of red and green but those who work for Canon seem to have it nailed.
Of course, some cameras do not have the facility to white balance, so what then? A red filter will make the most of what red light is present but of course you will need different degrees of red according to the depth you are at. You can fit alternate filters to a GoPro camera or you can fit a Backscatter Flip Filter system. This gives you the option to flip the appropriately coloured filter in front of the lens and make a judgement by looking at the image on the LCD screen. If you have a Hero 4 Black or an earlier GoPro 3 you can fit an LCD back available as an accessory.
A better way to get good colour in your pictures is to take some white light with you. In the case of video a constant light source is necessary and can vary in price from a basic rig to something more ambitious. You cannot have too much light but it needs to be of the right colour and exceedingly even in its spread, or your video camera will try to look into the shadows and the lit areas will burn out. You will need a lot of light to get good still photographs even for macro subjects when the light source is very close indeed. Even a high-output Swiss-made Keldan light has a limited range. For good still pictures there is no substitute for an underwater strobe or even a pair of them. They emit a quick burst of light but it is many times brighter for that short duration than any constant light source. These can vary in price from the Sea & Sea YS-03 and Inon S2000 to the bigger hitters like the Sea & Sea YS-D2.
Professional underwater photographers shoot RAW files and there is a very good reason why they do this. RAW files allow you to do a lot of adjustments to your pictures after you have been under water when there might have been time constraints. Many compact cameras can shoot RAW files but because these files can be very large it can mean a significant delay of a few seconds between taking pictures. DSLR cameras have buffers of varying size that allow users to shoot a lot of RAW files without this annoyance. Depending on what you are photographing, the delay between shots might be worthwhile.