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

Zoom lenses are lenses with a variable focal length. They allow the photographer to remain in the same position whilst varying angle of view(AOV) The angle that a lens can see usually measured across the diagonal of the frame, or image size. There are few applications underwater where a zoom is a genuine advantage however, although zoom lenses are an alternative to a range of interchangeable lenses on land.

As previously mentioned, it is better to stay close to your subject underwater and, as there are no close focus zooms available that go from 20mm wide angle to 50mm macroPhotography of smaller subjects shot (between 1:1 and 1:3) on macro settings or with macro equipment, you are still stuck with buying two lenses!

There is another good reason why zoom lenses are not much use underwater. Wide angleshots taken with lenses that have an angle of view significantly wider than a normal human perspective lenses require dome ports and macroPhotography of smaller subjects shot (between 1:1 and 1:3) on macro settings or with macro equipment lenses require flat portsOptical quality window in an underwater housing (by analogy with a ships port hole)., so how do you change ports as you zoom through your focal length range? In reality you choose either one lens (and port) or the other. It is generally accepted that 28mm is the widest zoom lens you should use behind a flat portA flat glass or plastic port that fits onto the front of the video housing, any wider you must use a dome.

Any zoom lens behind a dome portLens port constructed as part of a sphere of uniform thickness for wide-angle underwater photography. requires a plus diopterA unit used to express the power of magnifying glasses. Also used as a name for screwin magnifying lenses which can be fitted to the front of a camera lens. corrective lens - a piece of optical trash best avoided!

Most point and shoot cameras have zooms suited to land subject matter. Consequently you need to correct this with a supplementary lensadditional elements that can be placed over a prime lens to alter focal length and angle of view. Digicams can have two types of zoom; Optical zoomOptical zoom is a camera feature where the lens system physically changes focal length to zoom in on distant subjects and Digital ZoomDigital zoom is a feature that is more marketing ploy than anything else! Unlike Optical zoom which is produced by the lens system physically changing focal length digital zoom merely crops the image progressively..