3D with a single non-stereo camera
Effective 3D photography can be done using a single camera, with some limitations. The basic idea is to get two images which are separated by the same distance as the spacing between a normal person's eyes (about 65mm / 2.5") Two common methods of doing this are:
Shift left / shift rightSometimes called the "Cha-cha", this simple method is just like it sounds - you lean left, take one photo, then lean right and take another. Alternately you could slide the camera from one eye to another.
Slide barsOne of the drawbacks of "cha-cha" stereo is that it is easy to induce a rotation from one shot to the next - i.e. if you slightly rotate the camera between shots. This can be cured using a slide bar, which involves using a purchased or constructed slide bar and a single camera to make both exposures. The author has used an aluminmum plate with the edges folded to make a support against which the camera can rest, with a ruler glued to the back to determine the amount of image separation.
DrawbacksThe primary drawback of these methods is that nothing in the subject area should be moving between when the first and second photographs are made. Anything which has changed position in the photographs will cause what is called "retinal rivalry" - the brain has trouble fusing the two images. The things in the two photographs which have moved will appear to "flicker".
You'd be amazed at how often something is moving in what appears to be a static scene - leaves moving in the wind, cars in the distance, and so on!
AdvantagesThe advantages of single-camera 3D are clear: you probably already own a camera, and the results can be either free-viewed or viewed with inexpensive viewers, such as the View Magic print viewer. This means, of course, that you can see if 3D photography interests you before having to lay out a lot of cash for a dedicated 3D camera.
So in spite of the drawbacks, this can be a very useful method of 3D photography!
A Note About FlashIf you are using flash with a single camera slide bar (or shift left/right) approach, you may want to take special care when using flash. If you use the hot shoe on the camera (or a built-in flash) the movement of the flash between the two shots will create shadows that don't match up between the two exposures. This is sometimes called the "twin-sun" effect. You can avoid this by using an off-camera flash which does not change position between the two exposures.
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