FWIIW, I have had all three editions of Rule's book in front of me at the same time and was able to compare them. (The third edition is paperback.) The quality and clarity of the pictures is clearly different, the earlier the edition, the better the pictures. Sometimes it takes some magnification to see the difference, but then again sometimes magnification is used to pick out details of interest. I don't remember taking detailed notes, but if memory serves, the difference between editions 1 and 2 is not as pronounced as the difference between editions 2 and 3. Point is, if you are wondering if there is a reason to pay a premium for an earlier edition (apart from the collector value), if you care about the pictures the extra cost may be worth it to you. As far as I know, there was no revision of the text from edition to edition. My suggestion is to have a third edition (paperback) available to handle and read. These are available new for a bit less than $100. Then if you want, or if you happen upon a great deal, you can snag one of the first two.
