underwater Photo Course :: (2) Equipment Guide :: Underwater Camera Housings :: Lenses and optics

We still relate to the Focal LengthThe focal length of a simple symmetrical lens is the distance between the image plane (e.g. the film) and the middle of the lens when light from infinity is brought to a focus. of film cameras when describing the Angle Of CoverageThe angle between rays of light entering a lens from the extreme corners of a scene. AKA angle of view (AOV) of detachable lenses, even if used on digital SLR's. It is convenient to have one reference point but it is another source of confusion! Point and shoot camera lenses are often quoted as having an 'equivalent lens to...' .You must apply a Focal Length MultiplierThe Focal Length Multiplier is a figure to apply to 35mm lenses to calculate their true focal length on digital cameras that do not have full frame sensors. to lenses on digital cameras.

Lenses are identified by their focal length in millimeters (mm). The 'standard' lens for underwater photography is the 35mm - insofar as it approximates what you see. Your photographic opportunities would, however, be somewhat limited if the standard lens were the only focal length of lens available. The U/W standard lens is more like the 20mm, which has approximately 90 degrees angle of view.

Indeed, there are lenses where the focal length is less than the diagonal i.e. wide angle, and lenses with a focal length greater i.e. telephoto. Underwater photography suits the extremes of subject sizes. Subjects are either close and small (macroPhotography of smaller subjects shot (between 1:1 and 1:3) on macro settings or with macro equipment) or close and large (wide angle). The most useful lenses are therefore wide angle or those having close focus (macro) facility.