Hi, Thanks for this presentation! Just one comment, I notice the absence of two important types of lens: 1) The Von Rohr lens. It consists of two menisci mounted head to tail, hollow against hollow on either side of the diaphragm, with the 4 curvatures identical in absolute value or at least in pairs. Power is given by the thickness of the meniscus, field curvature is zero and distortion, coma and astigmatism are corrected, as is positional chromatism, due to symmetry, but obviously not longitudinal color and SA. Disadvantage: lens thickness. 2) In the same vein, the periscopic lens with two Wollaston menisci is more compact than the previous one, lower in cost but the curvature of field and astigmatism remain. With kind regards, Charles Rydel