Quote Originally Posted by maltfalc View Post
i hate having to repeat myself. i AM taking focus shift into account! this is the same arrangement as a speed graphic. the original position of the fresnel was between the gg and lens, with the plain side of the fresnel facing the camera's lens and the lens side of the fresnel in direct contact with the frosted side of the gg. that means the fresnel won't shift the focus any more or less than a plain sheet of acrylic. if the gg and fresnel are the same thickness, you can place the ground glass with the plain side facing the camera lens and the frosted side against either side of the fresnel or without the fresnel at all. the glass of the gg will shift the focal plane the same amount as the acrylic of the fresnel did, or at least close enough to not be noticeable. the focal plane is the same, both physically and optically. there's no uncertainty here. and aftermarket fresnels have absolutely nothing to do with anything i said.
maltfalc,

Perhaps I didn't understand your first post. Thanks for going to the trouble and repeating it for me in clearer terms.

Still, what you are suggesting isn't the norm. Ground glass is usually (if not always) installed by a camera manufacturer with the frosted side facing the lens. What you are suggesting is, in essence, to install the ground glass backwards and in the wrong position in the Fresnel sandwich on a camera that was designed to have the Fresnel screen between lens and ground glass in order to be able to remove the Fresnel screen and still maintain proper focus. Maybe that's necessary sometimes with Speed Graphics and Graphic View cameras (which came OEM with a Fresnel/gg sandwich with the Fresnel positioned between lens and ground glass) when the original focusing screen has become damaged or whatever. It's not much of a solution for someone looking to add a Fresnel screen to a camera that came with just ground glass or, as in in the OP's case, trying to find the original orientation of all the pieces when they've been disassembled and the order of reassembly isn't certain.

So, yes, removing the Fresnel screen and then mounting the ground glass backwards with the frosted surface separated from the lens by the clear glass on a camera that originally was designed to have a Fresnel screen of exactly the same thickness as the ground glass positioned between lens and frosted side of the ground glass will preserve the original design parameters and, therefore, keep the focus the same because the clear portion of the glass diffracts light and changes the position of focus the same amount as the Fresnel screen did.

I don't know if that's really relevant to the discussion here, but I do agree with you

Best, and keep cool,

Doremus