I have a copy of this book dated 1983 ISBN 0-9122160-25-5. When I read the quote from another APUG post I went to read more in my edition. There must be additional editions as my book only has 151 pages. Anyone know if Henry published additional editions. Using the books index I'm not locating the ref.I attach my sketch of results from "Controls in Black and White Photography" by R.Henry p240, for Tri-X Pan film in Beutler developer, indicating how density of a print from film exposed under a knife edge varies with distance.