Underwater Video

Home : Video course : Module 2: Video Housings : Underwater Lenses

One of the 'secrets' of underwater video is to get rid of the water! You must keep as close as possible to your subject, ideally within a third of the limit of visibility (to maintain good contrast).

At best, in tropical waters, the limit of visibility is 30 metres, (which means you need to keep your subject less than 10 metres distant). In UK waters, with an average of 3 metres Vis, you must keep your subject within 1 metre!

It goes without saying that the average camcorder is designed for land use not underwater use. Subject matter topside can be many miles away and so camcorder zoom lenses tend to be far too telephoto for u/w use. Most camcorders have a 10x zoom (meaning that an object appears ten times wider and higher at the telephoto setting than at the wide angle), some have 20x zooms. If you are familiar with stills camera focal lengths the average camcorder lens is equivalent to an incredible 50mm to 600mm zoom! Looking for an extreme zoom is therefore not a consideration when buying a camcorder for underwater use. Most of the shots you see in magazines are shot on much wider-angle lenses.

Another 'secret' of underwater photography is that even the most powerful lights do not penetrate further than 2 metres underwater (which is even more justification for keeping your subject close).

To overcome the problem of needing to be close to your subject whilst getting it all in shot you need a lens that has a wider view than normal. This necessitates the use of wide-angle lenses. Fortunately, you can make your camcorder lens 'wider' by attaching an extra lens to it (called a supplementary lens). Unfortunately, not all housings allow you the space to do this! Housings should come with a wide-angle lens as standard.

However, even with a wide angle lens there is another optical problem to overcome. Most divers will remember from their training that, due to refraction objects underwater appear closer and larger (when behind a flat port just like with your mask). The problem is that if you place a camcorder lens behind a flat port (even a wide angle) it becomes more telephoto (again the opposite of what you want). Fortunately, you can correct for this telephoto effect by putting the lens behind a hemi-spherical port (called a dome port) or by a supplementary lens.

Some camcorder housings give you the choice of interchangeable ports and are usually more expensive. As a general rule the larger the port the sharper the pictures. Larger domes also allow you to do pictures half in and half out, which can be very interesting and an ideal transition from the dive boat to the underwater action in your storyline.

Camcorder viewfinders are designed to be used with your eye up close but underwater you are forced away by your mask. This results in the viewfinder image appearing cropped at the edges. This makes composition difficult and reading the status information impossible! To remedy this some housings employ a viewfinder optic which allows full frame viewing (albeit with minimal reduction in image size).