Focusing without groundglass.

I know the title sounds weird, but here's what happened. The ground glass on my view camera (Wista 45 Metal Field *older version of SP) broke and now it only has the fresnel plastic left. I ordered a SatinSnow replacement but I know that will take several weeks to arrive, so in the meantime I'm left without a gg. I looked through fresnel it and it seems to show the image just fine. The question is, how accurate is this? Do I really need the gg?

If your subject is basically at infinity (say 40+ feet), stopping down 2 or 3 stops from your maximum aperture should probably cover any focussing errors.

I think that if you do this, you'll basically be focussing on the "aerial image", which means that the image may be in focus in your eye, but may not necessarily be in focus on the film plane. You can see this by holding the fresnel in your hand and moving it back and forth. You can focus on it even an inch behind where the film plane would be. The fresnel is a lens, so it's like adding another lens element! I've heard of people using plexiglass with some sort of "frosting" spray as an emergency gg, or try strips of scotch tape (the frosted looking type) on clear glass or plexi.

Search this forum for the thread about making your own ground glass. It is very simple and will take 1 day.

If you can put a target on the back surface of the Fresnel, where the ground surface of the original GG was, you may be able to get acceptable focus by focusing your eye on the target, then adjusting the camera until the scene comes into focus as well.

It might be simpler, however, to simply put frosted tape over the Fresnel (especially if the smooth side is toward you when you're under the dark cloth). If you use a good quality brand, it'll peel off readily and leave no residue when you're ready to install the replacement GG (and you did order two panels, so you won't get caught without a spare again, right?).

I have adjusted a couple of rangefinders and folders by using Glad Press'n Seal plastic as a temp grounglass. I just stretch it across the film rails for 35mm or use an old polaroid pack film case with the back removed and the plastic across the film opening. Seems to work great as it is nicely frosted and stays in place.