"Hypostereo" refers to a stereo image which uses a smaller than normal stereo base (the distance between the left and right lenses). Recall that "normal" image separation is about 65 mm, so anything closer together than this is, by definition, hypostereo.
As a general rule, the smaller the distance to the subject, the more demanding the requirements for the equipment and technique. The basic requirements are as follows:
- A means of precisely controlling the elevation and angle of the shots. Normally, you'll want the shots to be exactly parallel in the vertical direction (no rotation). Compensation for the offset in the two photos is taken care of when you set the stereo window.
- Precise control of the baseline (separation between the two images). For objects one to several inches across, it is recommended that you control the spacing to within about 1 mm.
- Control of the background, for when the subject does not take up the entire field of view. With focus at macro distances, distant objects will be badly out of focus. You may also want to allow more depth of in your subject by eliminating points at infinity. Some pieces of cloth can serve as a background, eliminating infinity objects in the final image.
- Proper lighting is important. In macro stereo photography, it's usually desirable to get the depth of field as great as possible, so you will usually set the aperture fairly small. To get reasonable exposure times, you therefore need a very bright light source, for example natural sunlight, bright lights, or a strobe. If you use a flash, it is important that the flash not move between exposures, as this would cause the shadows in the two images to not match.
For the first two requirements, a regular stereo "slide bar" can be used, especially if the magnification is not very great. The following table suggests the base separation for proper hypo-stereo photography:
Metric English Distance to Subject Lens Separation Distance to Subject Lens Separation 75 cm 5 cm 30" 2.0" 60 cm 4 cm 24" 1.6 45 cm 3 cm 18" 1.2" 30 cm 2 cm 12" 0.8" 15 cm 1 cm 6" 0.4"
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