Very interesting differences between the 1948 and 1981 editions. Thanks for posting the latter. It would be fascinating to know the reason for the change. That's a lot of years in a man's life. Did he change -- becoming less dogmatic? Did the materials change so that there was less difference between ortho and pan in 1981 than in 1948? Were filters different? I don't suppose it makes much difference to us today, but still, fascinating. Photography has such an intricate history.