As this one is still hot, may I clarify one point:
First, a great many M lenses were identical optically to either the preceding K lens, or to the following A lens, so I don't think that in those (many) cases anybody can credibly claim that the Ks or As were better.
I agree. If you look at the optical formulae on Boz's site, it's apparent that the majority of M lenses have the same optics as either the preceeding K lenses or the succeeding A lenses. After you factor out the lenses that were truly unique - like the 40 f2.8 and 150 f2.8 - there are only a handful of M lenses that have distinct optical designs and that can be compared to the K's or A's,
That K-series lenses share a lot with subsequent M and A-series is a myth. For their M cameras, Asahi practically redesigned its whole array of prime lenses.
Only the two macro f4 lenses (50mm and 100mm) and the 400/5.6 have retained their optical formula while going from K to M. All other M lenses were new designs!
Some M lenses have the same focal lenght and aperture than their K counterparts but have a different number of elements: 20/4, 28/3.5, 28/2, 35/2, 120/2.8, 135/3.5, 200/4, 300*/4.
Other M lenses have either a new focal lenght (100/2.8) or a new maximum aperture (35/2.8, 85/2, 150/3.5). These have either a different number of elements (35, 85), of groups (100) or a different optical pattern (150).
The 50/1.7 has both a new focal lenght and a new maximum aperture. It shares the 55/1.8 pattern (like most 1.7 and 1.8 normal lenses for SLR) but, to reduce costs, the doublet in the M lens has a flat joint instead of a curved one.
The M50/1.4 is also a new design. It shares the same basic optical pattern as the K50/1.4 (like practically all 50/1.4s) but shows differences in the form of some elements (shape, thickness, curve) and the space between some of them. It kept the curved joint in its doublet. (The M50/1.4 lens was again modified to give the A version.)
New sub-thread...
The "A philosophy" took from both K and M philosophy. From K because non-M lenses were offered as A lenses (15/3.5, 24/2.8, 50/1.2) while new A lenses were designed without portability in mind (85/1.4, 135/1.8, and the long 2.8 guns). From M because many M lenses made it to the A-series without any modification (28/2, 28/2.8ii, 35/2, 35/2.8, 50/1.7, 100/2.8, 100/4 macro, 300*/4) while some of the new lenses were small and light (20/2.8, 50/2.8 macro, 135/2.8, 200/4, 400/5.6).
My interest in philosophy dropped when the F lenses appeared as the zoom lens became the new paradigm...
Andre
