I have once more read Erwin Puts on the details of pursuing mechanical and optical perfection in developing Leica optics. ISBN 978-94-91089-12-1,
Most interesting details, starting with the improved triplets that became the quadruplet Elmar and moving on through the Hektor to how the summicrons were improved while discussing how to measure performance. A useful summary of lens design and production even if one does not use leitz products.
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