LightPath has been actively commercializing a family of axial-gradient glasses called the GSF glasses. These glasses have the same dispersion and refractive indices found in the conventional SF glasses. Therefore, in polychromatic design, it has only been possible to apply the extra degrees of freedom offered by GRADIUM$+TM$/ to negative elements by replacing a flint glass. This has shown that GRADIUM can significantly and positively affect polychromatic designs. For example, a seven element double Gauss lens was redesigned with GRADIUM, resulting in a six element design and a 27% improvement in rms spot size. Similarly, the Kodak Ektapro varifocal projection lens was redesigned reducing the element count from seven to five. Despite these impressive results, since most of the work done by any polychromatic system is done by positive elements - typically crowns, it is clear that the real potential of GRADIUM to polychromatic design could not be unleashed until GRADIUM crown materials were available. The GRADIUM GK glass family is one of several GRADIUM crown families under development. A number of examples will be presented to illustrate the advantages realized in optical design when GK glasses are used. Simple doublets as well as more complex multi-element systems will be discussed, some of which use both GK and GSF glasses and others which use only GK or GSF glasses.
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