Teaching optics - Possibilities of aberration correction in a single spectacle lens

Spectacle-wearers make up a considerable part of present-day society, so spectacles are one of the most popular optical instruments - very simple instruments since they are in fact single lenses. On the other hand their mode of operation and the demands for imaging quality are very specific. Therefore spectacle lenses are interesting objects for aberration analysis and are excellent examples for illustrating purposes while teaching geometrical optics. Typically, the spectacle lens is fixed at some distance in front of the eye. When looking at distant objects, the eye rotates around its centre of rotation while the field-of-view angle is limited practically only by the spectacle frame. The chief ray, connecting point of fixation and centre of eye pupil always passes through the eyeball centre of rotation. Therefore we can assume that spectacle lens has shifted output pupil while preserving a relatively large field of view. Consequently, it is important to correct field aberrations, in particular astigmatism. It is interesting to investigate relationships between spherical aberration, coma and field curvature each as a function of output pupil shift and to point out that it is possible to correct My astigmatism and minimise spherical aberration or coma.