Although popular interest in stereophotography has waxed and waned several times since the introduction of the Holmes stereoscope in the 1850's, the importance of stereophotography in scientific and technical applications has steadily increased. It has been of great value for contour mapping in geophysics and cartography, for displaying crystal and molecular structures, for locating and viewing internal structures in radioscopy, and for presenting 3-dimensional images obtained by optical microscopy, by x-ray projection microscopy and by electron microscopy.A persistent problem limiting the wider use of stereophotography has been the problem of viewing the image. Because stereo viewers are awkward to use, other methods of stereo viewing have been developed, including the following: 1) “reading in 3-D” with the use of eye training; 2) the use of a stereo pair with one image printed backwards and viewed with a plane mirror between the images; 3) the hologram method and 4) the parallax stereogram method.