Fresnel lens I ordered just arrived, although the size is not totally fit for my ground glass, but still covers 95% area of image.
Compared with/without Fresnel lens mounted, you can clearly tell the difference. It will be a standard accessory with ground glass panel, free for each converted camera.
I am waiting for fine grain acrylic glass, to replace the one now I use, which is a transparent acrylic with a matt paper.
(20/08/09 add) Now the acrylic has come, and perfectly fit for the panel, you can compare how Fresnel lens affects the projected image. The lens in use is Schneider Symmar-S 5.6/100mm.