Quote Originally Posted by bglick View Post

Sandy, when I read your lppm, I assumed it was a typo, and assumed lines per mm. I should have mentioned that. I hate the way these lpmm, lppmm, lp/mm is tossed around so loosely. Assuming the author truly meant line pairs per mm, then I would suggest his assessment is pretty high compared to most data i have read. What is the copyright of the book?

I can assure you, the eye can not resolve 20 lp/mm, even under the best of circumstances. Grab a test chart and try it, you can't fathom how tiny these targets are. Again, you can double the target size, and double the viewing distance to 20" to test yourself assuming you can't close focus.
The use of lppm is mine. John Williams uses "lines per millimeter" throughout the text. Not lpmm or lp/mm. I meant the term to mean one white line and one black line in every mm, thus line pairs per millimeter, or lp/mm.

There appears to be a lot of confusion on this with photographers, because many use lpm for lines per millimeter. But lines per millimeter in Williams' text is understood to mean line pairs per millimeter.The book was published in 1990, in the very early days of digital imagery. But it is still a good read.

Frankly there would be no need for me to get out a chart and try to resolve (pun) the issue with my eyes. I used to have 20/20 vision but now have very severe astigmatism in one eye, and the other is myopic and has a cataract that will need to be removed in a year or so. Also, I had a retinal tear last year in the myopic eye that caused some loss of vision. Fact of the matter I should probably quite talking about high resolution imagery and start working wth one of these "artsy fartsy" Holga cameras, or even the mythical Diana if I could afford one of those plastic marvels.

Sandy King