Perspective Projection - Transformations and Projections in Computer Graphics - page 125

Figure 3.45: A Jig to Photograph a Stereo Pair.

The jig consists of two pieces of wood or plywood that are attached to the tripod
with a clamp. The camera is placed on the wider piece, while the smaller piece serves
as a support and guide. The dimensions of the two pieces depend on the size of the
camera and the length of the required baseline. Before taking any pictures, mark two
points on the guide, about 6.5 cm apart, to serve as marks for the standard baseline.
With a bit of experience, this primitive device produces very accurate stereo pairs. It
is easy to come up with variations on this simple design.
Good-quality kitchen cabinets often have drawers mounted on special ball-bearing
metal slides. Anyone planning to take many stereo pictures might want to attach a
camera to such a slide and attach the slide to a heavy-duty tripod. Such an arrangement
is accurate, easy to use, and lasts a long time. Detailed instructions are available at
[berezin 06]. Similar devices are sold commercially by [photo3d 06] and others.
A completely different approach to taking such pairs of pictures is to make or obtain
a pair of cameras whose lenses are placed the right distance apart and are operated
together with a common shutter release cable (Figure 3.46). Such a device can produce
stereo pairs of scenes that change rapidly, such as flocks of birds or racing cars. The two
cameras can be placed either side by side [part (b)] or one above the other, as long as
the distance between the centers of their lenses is the right one. If one camera is placed
on top of the other [part (a)], it is important to leave enough room between them for
the shutter release cable. If the cameras are mounted bottom to bottom, care should
be taken to align their lenses vertically [part (c)]. In the latter case, the user should
verify that the two pictures are vertically aligned (rule 3 above). Every point should be
at the same height in the two pictures.

(a) (b) (c)

Figure 3.46: A Pair of Cameras.