If the fresnel's behind the ground glass it makes no difference, by behind I mean viewing side. If it's on the inside it'll move the screen back focus is always on the ground side of the screen.
So a back is modified if a fresnel is used on the inside between screen and lens, and conversely if a back was designed for an internal fresnel the screen needs shimming to reset the focus if the fresnel is removed.
Last edited by Ian Grant; 10-22-2011 at 04:52 AM. Click to view previous post history.