The use of low departure aspheric surfaces in high quality wide angle lenses

Abstract

Modern lens designs for digital sensors, such as those required in medium volumes for cinematography, often require the use of one or two high departure aspheric surfaces. With departures from best fit sphere of up to a few millimeters, the use of such surfaces are accompanied by a number of consequences: high cost metrology, very tight opto-mechanical tolerances and image artifacts due to the sub-aperture grinding and polishing process. Previously we examined the use of multiple aspheric surfaces with very low departures from best fit sphere (BFS) and concluded that advantages may be gained in standard and telephoto lenses, but not in wide angle lens designs1. In this work we consider the potential benefits of low departure aspheric surfaces, as applied to wide angle lenses in particular. We review the number, placement, and nature of aspheric surfaces in some wide angle lens design examples, and look at the potential to redesign with an increased number of low departure aspheric surfaces that have the potential to be manufactured without the need for computer generated holograms (CGH’s). The use and limitations of modern interferometers capable of measuring aspheric surfaces without the use of CGH’s will be considered. In one example we examine the performance, manufacturing, and cost perspective, paying particular attention to testing and mechanical alignment tolerances.