Split Images
Another format considered part of underwater photography is the over/under or split image, a composition that includes roughly half above the surface and half underwater. The traditional technique was pioneered by National Geographic photographer David Doubilet, who used it to capture scenes above and below the surface simultaneously. Split images are popular in recreational scuba magazines, often showing divers swimming beneath a boat, or shallow coral reefs with the shoreline seen in the background.
Over/under shots present some technical challenges beyond the scope of most underwater camera systems. Normally a wide-angle lens is used, similar to the way they are used in everyday underwater photography. However, the exposure value in the "air" part of the image is often quite different from the one underwater. There is also the problem of refraction in the underwater segment, and how it affects the overall focus in relation to the air segment. There are specialized split filters designed to compensate for both of these problems, as well as techniques for creating even exposure across the entire image. Some photographers also use extremely wide or fisheye lenses, which have enough depth of field to overcome any differences in focus. One must also take into account the "dome" of the underwater camera housing. A wider dome is better for over/under shots as it lets the water rest. Some photographers use an external flash on a low setting to overcome the difference in usable light in the two areas.
Digital darkroom techniques can also be used to "splice" two images together, creating the appearance of an over/under shot.
Read more about this topic: Underwater Photography
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