Macro or wide-angle? 35mm? 20mm? 15mm? What lens DO you choose for your underwater photography? Lens are like tools. You need to use the right tool for the job. But they are also an extremely important tool, the most critical of all the components of an underwater camera. A lens is what bends the light, focuses, and otherwise prepares the light before it hits the film (or digital chip). If the light is not prepared properly, image quality suffers. You should purchase the best quality lens you can afford.

BY THE NUMBERS

Lenses are measured by millimeters (mm) in "focal length" or the distance from the optical center of a lens, focused at infinity, to the point behind the lens where a sharp image results, generally the film plate. The smaller the number, the wider the angle of the lens or the larger the subject area is recorded on the film. "Normal" focal length on a 35mm camera (the 35mm indicating film size, not lens size, a common point of confusion) is about 50 to 55mm. For land photography, a 55mm lens would give you about the same image on the film as you see through your eye with no magnification or shrinkage. A standard 55mm is not, however, a good lens for underwater. For good underwater images, you need to get close to your subject.

LENSES AND GETTING CLOSE

Water is a giant filter, the more water between your subject and your lens, the more filtering and fogging, even in clear water. Most really good underwater photos are taken at five feet or less from the subject - yes, even with huge fish and whales. Because of this there are only two practical lens arrangements for underwater photography: wide-angle and macro.

WIDE-ANGLE

The only way to get an entire large subject or scene into a photo, yet still be close, is with a wide-angle lens. The wider the angle, the more of the underwater scene you take in. The lenses that are excellent for underwater photography are the 15 and 20mm lenses but can be expensive. In my book, they are well worth the investment. A 28mm lens will do the job fairly well. The 35mm lenses are good for surface photo wide-angle photos, okay for underwater work, but best used with supplemental macro equipment.

MACRO

A "macro" lens is for photography of small subjects at close range. A macro rig can be built in one of three ways. A 35mm wide angle lens can be equipped with either an extension tube or a supplemental lens. An extension tube will give you the best quality image, while a supplemental lens often gives you the option of removing it if needed for wide-angle photos. Extension tubes and supplemental lenses for macro photography are inexpensive and provide sharp photos. Most supplemental lenses or extension tube rigs, however, require the use of a "framer" to know just where the lens is in focus. This is a noted disadvantage in photographing skittish fish.

The third option is a housed land camera equipped with a macro-capable lens. The lens is often a mild telephoto, around 100mm, that allows the photographer to zero right in on the subject yet maintain distance. The lens may or may not be auto-focus but most pros prefer to preset the focus, then move the camera in and out to compose the shot and bring the subject into focus as desired. For creativity and approaching a variety of animals, this is the superior arrangement for macro photography. It is, however, expensive.

Whether extension tubes, supplemental lenses or a housed rig, macro photography is often expressed in ratio number such as 1:1, 1:2 and 1:3. It is really simple: 1:1 means that the image on the film is the same size as the subject photographed. An image half the size on the film as the original subject is expressed as 1:2 and 1:3 is 1/3. Which brings up another added advantage of a housed macro rig - the ability to move between macro image sizes including all ranges between.

CLOSE-UP CONFUSION

A common confusion is that "macro" means "close-up" photography and wide-angle is from a distance. I have taken wide-angle photos with the subject mere inches from the lens and also macro photos with subjects two or three feet away. Macro does not mean close-up. It does, however, mean your subject (or subject area) will be small, almost always less than eight inches and usually around two to four inches in size. Macro means small.

Savvy underwater photographers, beginner or experienced, keep their lens cache simple with two, maybe three choices. It is especially important you keep yours simple as you learn in order to not get caught up in the all the mm, numbers and lens lingo.