I have a Toyo Field 45A which has a camera back with a Toyo fresnel lens placed in front of the ground glass. I used to use the Toyo 3.6x loupe for fast focussi ng and then I refine the focussing by using a 30x microscope magnifer. I have be en quite confident that I can obtain the most accurately focused images possible and in fact I have been quite happy with the results. Today I bought an identic al spare ground glass without a fresnel lens. I intend to carry one spare ground glass in case that I break the focussing screen in the camera back, I can have one to replace. I did not buy the fresnel lens because I don't want to spend the extra money. When I got home I became aware that the thickness of the focussing screen with a fresnel would be different from that without a fresnel lens and I suspect focussing discrepancy would result. I then used a standard lens (set to f5.6, focus on a bright object 3m away)to test the focussing with and without t he fresnel lens. The result is there is minor shift of focus observed on the scr een under 30x maginfication. The observed difference in focussing would only dis appear when I stopped down the lens in either case to f11 . I have not had a cha nce to test the focussing on the film and I am not sure under which scenerio I can have a more accurate focussing. Any comments and suggestion will be appreci ated. Thanks in advance. C.W. Lee