the hologram will act as a lens. In fact, except that the transitions between 
transparent and opaque areas are gradual, the hologram is the same as a 
Fresnel zone plate which also has an image forming capability. We may 
look upon this concentric circle hologram as a holographic spherical lens. 
Similarly, by using a point and a line to form the hologram, one can obtain 
a holographic cylindrical lens. The holographic equivalent of a prism can 
also be designed and is, in effect, a series of equidistant straight lines 
with a sinusoidal transmission in the direction perpendicular to the lines 
similar to a diffraction grating. Thus, it is possible to develop holographic 
equivalents for all ordinary optical components. It would seem feasible, 
in view of this, that an imaging system consisting of holographic optical 
elements could be realized and that this holographic analog would perform 
in the same fashion as the conventional equivalent. If this is the case, 
there are interesting possibilities where one is concerned with recognizing 
an object from a variety of aspect angles through comparison with a stored 
master object. Conventional optical elements are large and relatively 
inflexible. Physical considerations make it impossible to have a great 
number of optical elements that could be rapidly interchanged to make a 
truly flexible optical system. Holograms, however, are just photographic 
transparencies and a very large number could be stored as a library of 
lens elements which could be brought into position as required. One can 
envision these holograms being selected by an on-line computer to produce 
virtually any optical transformation desired. There is also the possibility 
that the holograms themselves could be generated by an on-line computer to 
eliminate the need for storage and to allow continuous variation.