Wavefront coding eliminates elements in lens design
System integrators attempting to reduce the cost of their imaging systems have had difficulty replacing traditional glass lens elements with plastic lens elements. Although plastic elements can reduce system costs and produce lighter-weight systems, thermally induced changes in plastic can create misfocusing errors. Now, through a combination of specialized optics and digital processing techniques, CDM Optics Inc. (Boulder, CO) has developed a method that uses aspheric designs to control temperature-related misfocus and to limit chromatic aberration.
"Traditional lens designs often use many lens elements and optical materials to accommodate for chromatic aberration," says Ed Dowski, vice president of engineering at CDM Optics. Using CDM Optics plans, designers can reduce the number of optical elements or materials needed to control chromatic aberration.
"Glass or plastic singlets of a material used in place of glass doublets can control chromatic aberration over a wide range of wavelengths," Dowski says. In addition, the technology can eliminate lens elements in designs used for the control of spherical aberration, astigmatism, and field curvature.
CDM combined two off-the-shelf singlets in a lens system consisting of a Model E32903 200-mm singlet and Model E32718 100-mm singlet from Edmund Scientific (Barrington, NJ). Spaced 43 mm apart, the optical system exhibited a focal length of 78 mm and an f-number of 11.
"Simple lens designs of this type will usually have large axial © chromatic aberration," says Ed Dowski. To compensate for this, CDM added an aspheric cubic phase surface between the lens elements and used color-independent digital processing to process the resultant image.
In the system without the aspheric element, the large amount of color in the resultant image is due to each color component focusing in different planes. When the aspheric element is added and the resultant image computed, all the colors of the image are brought to focus independently and form a clear image with no loss of spatial resolution.