some thoughts on lenses

Concept of Metasurfaces.
Courtesy of Penn State

Toronto. Thanks to friend and member Russ Forfar for this idea about future lenses.

Before photography, we had microscopes that needed quality lenses (objectives). Initially, the design was “cut and try”.

Designers tried to combine glass elements made with different glasses and curvatures to improve resolution and reduce distortions (geometric, astigmatic, spherical, etc.).  The goal was to have two or three colours come to focus in the same plane. Photography meant that the plane had to be flat as well all across the light sensitive glass or metal plate material.

Ernst Abby  applied mathematics to the problem and challenged glass maker Otto Schott to create glass meeting his criteria.  People became skilled as “computers” and calculated various points on a flat plane based on the specifics of each element. Different curves and glasses were calculated in attempts to improve resolution and speed while reducing distortion. This lead to classic lens designs of multiple elements.

In the 1950s, Leitz used modern day electronic digital computers to do the necessary calculations vastly reducing the time taken and increasing the accuracy of the results. Modern lenses are designed with even faster computers and a vast array of glasses.  Some elements are even made with aspherical surfaces to improve resolution, reduce distortion, and reduce the number of elements needed. Some zoom lenses resort to actually moving a group of elements to retain resolution as focal length is changed.

A recent trend has been to vary the glass characteristics within an element, culminating in the potential of creating a usable lens consisting of a single element as described in this  Penn State article.

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