The Ctein article on focusing was discredited long ago.
I should qualify this: Ctein published an article in the early 90's advocating focusing through a blue filter, and claimed that not using a blue filter resulted in a 1/2" to 1" error in focus wrt the paper position. The claim was rebutted in letters to the editor and a subsequent article. I see Ctein no longer makes his original claim.
Last edited by Nicholas Lindan; 10-27-2012 at 05:17 PM. Click to view previous post history.