'What does forcing the perspective mean, and how do I go about it?' - Glenn S., Boston, MA
The good news is that the answer is not complicated, and understanding how and when to force perspective can add a lot of impact to wide-angle images.
Forcing perspective is a great way to add impact to your wide-angle photographs.
On land, human eyes see approximately the same field of view as that recorded by a 50mm lens on a 35mm camera. As a result, when you use a 50mm lens in topside photography, you are said to be using a normal lens. Underwater, due to refraction, a 35mm lens is said to be a normal lens. Take a photograph of a diver, and the relative size of body parts such as the head and hands appears normal.
Photographs created with telephoto lenses such as a Nikon 105mm have a completely different look, or perspective, than images made with a normal lens. Small fish can look huge in images made with telephoto lenses, and backgrounds appear to be very close to foreground subjects.
These photos are good examples of normal (photo #1) and forced (photo #2) perspective of the same subject.
Lenses such as a Nikonos 15mm, Sea & Sea 16mm and Sea & Sea's ultra-wide 12mm fisheye have much wider angles of view than normal and telephoto lenses, and they are commonly referred to as wide-angle lenses.
On land, there is a tendency for photographers to back away from their subjects when using a wide-angle lens. But you do not have to back up with a wide-angle lens, on land or underwater. In fact, in many instances you can add of impact if you use a wide lens and get very close to your foreground subject. This emphasizes the foreground subject, making it appear larger and more prominent than it normally would. Objects in the background appear smaller than normal in your photographs, and visibility looks better in your picture than it was during the dive, as background objects appear to be farther away. In addition, the less water you shoot through, the sharper your images and the more vivid the colors in your foreground subjects, especially those that are lit by a strobe.
Consider the following scenario. A diver who caught a lobster might like a photograph of himself with his prize. If he holds the lobster close to a wide-angle lens while he is an arm's length away, the bug will look huge and the diver will look small. The photograph will look like the caption should read: "Boy catches biggest lobster in history." You can create a similar effect with such subjects as crinoids, seafans, sponges, fishes and even shrimp, as long as they are not too small.
Getting close forces the perspective by providing a view that we do not normally see with our eyes or with a normal focal length lens. My suggestion for Glenn, and any wide-angle photographer, is to try forcing the perspective and see if you like the results. A forced perspective is not right for every situation, but when it is, you will make a big impression with your audience.
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