Historically speaking - development of photographic lenses

PSA Journal, June, 1991 by Tony Patti

Did You Know That good lens designs did not come about until glassess having different indices of refraction were developed? Barium crown glass was not developed until 1894 and was a great stride in correction of optical aberrations. One of the first significant developments in optics was the rectilinear lens which solved the problem of vertical lines appearing curved at the edges of pictures. Another break-through in lens design was development of the anastigmat lens which provides good resolution in any direction at right angles to the lens axis. Until the early nineteen hundreds there was a limited ability to correct astigmatism in lenses. Any correction of astigmatism was accompanied by increased curvature of field.

At the turn of the century, symmetrical lens systems began to appear. This lens system was first mentioned at about 1850. A symmetrical lens is one where the configuration of the front elements is a mirror image of the rear elements. The design gives automatic correction of three of the seven aberrations in lenses. The lens designer working with a symmetrical system need only concern himself with correction of spherical aberration, chomatic aberration, curvature of field and astigmatism. Although lens aberrations are sometimes referred to as distortions, only one aberration is distortion, and that is rightfully called distortion. Distortion is further defined as pin cushion or barrel, depending on the direction of bending of straight lines at the edges of the photographic image.

The relationship of element surfaces in a lens design in such that a change in any one surface will have a significant effect on the function of all other surfaces. This was a problem of large magnitude in the days before the computer as we know it. It may be interesting, if not surprising, that lens development that required years of calculation prior to the computer can now be done in hours, if not minutes, by use of modern, powerful computers. We have come a long way since the single element, or meniscus lens and quite likely most of us have little or no regard for the amount of work that made present day optics a reality.