By the way, dear friends. This is a nice and short article with pictures, about the Fresnel lens, how it is made and work.

http://en.wikipedia.org/wiki/Fresnel_lens

Please read it and try to explain me how it works, when the lens installed after the ground glass (mean between the ground glass and photographer) and with grooved surface of the Fresnel facing the ground glass.

In my opinion it is understandable how the Fresnel works when installed before the ground glass (mean between lens and ground glass) and with grooved surface facing the ground glass. It just sending a parallel ray of light thru the ground glass. We all know that the ground glass by itself a diffuser. So with the Fresnel before, it seems like less light will be diffused by the ground glass, and image what photographer see on the surface of the ground glass will be much brighter then without the Fresnel.

But what the Fresnel really do when located after the ground glass with grooved surface facing the ground glass?
Thank you.