Sold my Panasonic 20mm for the 25mm WHAT A DIFFERENCE "wow"

While this is right to an extent, the reasons are not. Remember that lens coating, invented by Zeiss, was not invented until just before WWII and not available on commercial products until after the war. Pre war, Zeiss had a range of fast lenses, the Planar and Sonnar. The Planar had 8 air/glass surfaces, and without coating would never be contrasty. The Sonnar had only 6 and was more contrasty but nowhere near as sharp. Leitz simply did not have fast lenses. You could buy a Schneider Xenon which was a double gauss like the Planar, and performed the same. When Leitz brought out its own double gauss, the Summar which was even lower contrast than the Planar. After the war, the Zeiss coating patents were expropriated by the Allies and became generally available, including in occupied Japan. Coating provided the means to make high contrast lenses with more air/glass surfaces, which in turn meant that lenses faster than f/2.8 with high contrast and sharpness became a possibility. Pre war, the 'Leica look' was the less sharp more contrasty images produced by slower lenses with fewer elements according to the pragmatic design of Max Berek, Leitz simply could not match Zeiss (or for that matter Voigtlander) for sharpness, but then they were a much smaller company, without the resources.

Not really. Firstly, mostly they 'copied' Zeiss designs, and the 'they' was Nippon Kogaku. Secondly, it is a myth that the designs were 'copies', yes they used the expropriated patents for lens configurations, but were recalculated and introduced some novel design features. The later (mid late '50's) Japanese optical works such as Asahi, Canon, Zunow, Mamiya, Minolta also started off making independent versions of the Nippon Kogaku lenses, and then branched out to some highly innovative designs. What isn't true is that the Japanese companies use 'cheaper glass' and 'more lax tolerances'. In fact, the Japanese companies were at the forefront of using rare earth glasses, and their tolerances were as good as anywhere.

Neither of those things is true. The major difference between the Nippon Kogaku philosophy of design and the German one is that the Germans designed for flatness of field and even resolution across the frame, whereas Nippon Kogaku emphasised sharpness at the centre of the frame. The outcome was that in the centre field, where the subject usually was, they were sharper than the German lenses. Post war, under the direction of Walter Mandler, the Leica philosophy changed somewhat, to the pursuit of excellence at elevated prices.

The IC (Integrated coating) lenses appeared in 1971, long after the F (1959) was already established as the PJ's camera of choice. Already, Pentax had SMC and Zeiss T*. The early F lenses carried on the design philosophy of Nippon Kogaku's RF lenses.

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Bob