ABSTRACT
The word 'lens' was probably adopted in the seventeenth century when Robert Hooke, Anton van Leeuvenhoek and others made small hemispheres of glass for use as objective glasses in their microscopes. These had the appearance of lentils and lens is the latin word for lentil. In many languages the same word is used for both. It is therefore technically superfluous to refer to 'refractive' lenses or lenslets because it is through refraction at the surface that a lentil-shaped piece of material will form an image. Current practice, however, appears to be to call anything that will form an image a 'lens', so that a Fresnel-zone plate is a 'diffracting lens' and some authors have even referred to concave mirrors as 'reflecting lenses'. Nevertheless, it does no harm to remind ourselves that in studying arrays of 'microlenses' or 'refracting lenslets' we arc returning to the origin of the word itself.
