Underwater videography

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Underwater Videography is the branch of underwater photography concerned with capturing underwater moving images either as a recreational diving or commercial documentary or movie making activity.

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[edit] Limitations of Underwater Video

The primary difficulty in underwater camera usage is, of course, sealing the camera from water at high pressure, while maintaining the ability to operate it. The diving mask also inhibits the ability to view the camera image and to see the monitoring screen clearly through the camera housing. Previously the size of the video camera was also a limiting factor, necessitating large housings to enclose the separate camera and record deck. This results in a larger volume which creates extra buoyancy requiring a corresponding use of heavy weight to keep the housing underwater (about 64 lbs. per cubic foot of displacement or 1 kilogram per litre in the ocean). Early video cameras also needed large batteries because of the high power consumption of the system.

A final problem is the lower level of light underwater. Early cameras had problems with low light levels, were grainy, and did not see much color underwater without auxiliary lighting. Large unwieldy lighting systems were problematic to early underwater videography. And last, underwater objects viewed from an airspace, such as the eye inside a mask or the camera inside a housing, appear to be about 25% than they are. The photographer needs to move farther back to get the subject into the field of view. Unfortunately that puts more water between the lens and the subject resulting in less clarity and a reduced color and light.

[edit] Modern Improvements

Today, the small size of fully automatic camcorders with large view screens and long-life rechargeable batteries has reduced the housing size and made underwater videography an easy, fun activity for the diver. Low-cost wide-angle lens add-ons are available for many cameras and some can even be fitted outside the camera housing for versatile use. This lets the photographer get closer and make the subject clearer and also with fewer focusing and depth of field problems. Today cameras are more sensitive to low light conditions and make automatic color balancing adjustments. Nevertheless, deeper water videography still needs auxiliary light sources to bring out colors filtered out of sunlight by the distance it has travelled through water. The shortest wavelengths of light are lost first (reds and yellows) leaving only a greenish or blue cast in deep water. Even a hand light will help show off some of the magnificent colors of a coral reef or other marine life if used during taping.

[edit] Video Housings

Most modern underwater housing are pressure resistant to about one hundred feet, the practical safe depth of sport-diving. Typical construction is from molded polycarbonate plastic, or aluminium for more professional systems. They usually have quick release snaps, an o-ring seal, and through housings fittings for several camera controls. A few are generic in nature from several manufactures such as Ikelite, They may be adaptable to several camera sizes. Most housings, however, are specific to a particular camera type and may be marketed by the camera manufacturer or an after-market company.

Occasionally housings might be advertised as "water housings" rather than underwater housings. Water housings are not intended for deepwater use, but rather are "splash housings for use around the pool, in rain, or to protect against falling overboard. At the most they are for very shallow activities - usually not more than about 1 or 2 metres / 3 to 6 feet in depth. One particular manufacturer offers a plastic bag type solution with a watertight seal, and a glass port front. The flexible bag allows some modest camera control, but suffers greatly when taken deeper since the bag compresses from the pressure and makes controls nearly impossible to operate. These are usually limited to snorkeling activities.

[edit] Camera Selection Tips

If you have a camera you like, locate a dedicated housing for it as soon as you can. Most are models are produced in limited runs and both the camera and housing may cease to be manufactured in just a couple years. If purchasing a new system, it is wise to check the availability and cost of a good housing before buying the camera. Try to stick with the most popular models from Sony, JVC and others for the highest likelihood of finding a companion housing. See if it can accommodate a wide-angle adapter and a long-life battery on the camera. Polycarbonate (sometimes called Lexan) housings tend to be most compact, cheapest, and easiest to use - not to mention being less subject to condensation or fogging in the housing. They are quite sturdy, though somewhat more subject to scratching under hard use (lenses are glass however for good optical qualities).

[edit] Still/video combinations

Most current digital still cameras are also capable of what is sometimes referred to as "Internet Video". This is usually a variation of the MPEG video standard of digital imaging created as a streaming series of digital images, with some advanced compression techniques. Names you might recognize are Quicktime Video or Real Video, .WMV, or .AVI files. These file formats are usually limited in display screen resolution (measured by pixel height by width) and are not intended to be played on anything larger than a computer screen. Recording options are limited and quality is usually at the low end (for example 640x480 screen size or even smaller). Capacity is often limited by the SD card or CompactFlash card in the camera.

A dedicated video camera, on the other hand may also have a "still frame" or snapshot capability. This is a better choice if the first intent is to have high quality moving pictures and an occasional still picture. Camera capacity, based on videotapes, or even harddrive recording is usually at least 2 hours, and necessitates very little opening of the housing during the dive day. Check the Pixel quality (4 megapixel or above preferred) on the video camera capability if this is of interest. For the best results, Hi-definition video cameras have recently arrived (1080i) which, like high definition television screens, will provide the best of quality and image resolution.

[edit] External links

http://www.ScubaMagazine.net Underwater Photo, Video, Travel & Dive Discussion Community, a multimedia capable interactive community