I've been amazed at the excellent optical quality of RF images, and went looking for answers to many technical questions that I had (being the engineer that I am). I found this link on the web which was extremely insightful. Sharing it with the rest of clubsnap members who're interested in RFs. 
Here: http://www.photozone.de/3Technology/camtec2.htm
cheers,
sfhuang

Here: http://www.photozone.de/3Technology/camtec2.htm
cheers,
sfhuang