Lens Design Fundamentals, 2nd Edition

Chapter 13

Symmetrical Double Anastigmats with Fixed Stop

13.1 THE DESIGN OF A DAGOR LENS

For 25 years after the introduction of the Rapid Rectilinear lens, designers tried unsuccessfully to modify it in such a way as to reduce the Petzval sum, and so remove the astigmatism that limited the performance of the Rectilinear in the outer parts of the field. In 1892 the German designer von Höegh¹ made three useful suggestions to mitigate this limitation: (1) to insert a collective interface convex to the stop in the flint element of the Rapid Rectilinear, thus turning the half-system from a doublet into a triplet; (2) to use progressively increasing refractive indices outward from the stop; and (3) to use almost equal outside radii of curvature and to ...