I recently purchased a Wista SP 4x5 fields camera, and I'm experiencing a strange effect with the included ground glass. At normal viewing distance (8" or 9"), closing the left eye leaves the left half of the screen dark, and closing the right eye leaves the right half of the screen dark.

The result is that I'm experiencing a disturbing effect, when both eyes are open. I've never encountered this before, and I suspect it has to do with the focal length of an integrated Fresnel lens. (It sure appears to include a Fresnel lens, given the brightness of the image.) Is this strange effect characteristic of these cameras? Unfortunately, the screws are too tight and too small for me to remove the ground glass, and I don't want to risk stripping the Phillips inserts. Otherwise, I could get a better look at the construction of the viewing system.

My guess from a Wista Fiel 4x5 that I have, is that the SP has a two layer affair: one layer being a thin sheet of glass with the grid on it, and a second piece of plastic that may be an integrated Fresnel and matte surface for focusing. So, this raises another question of whether I can use only a Wista product designed for the camera (like Arca Fresnel lenses), or swap in any suitable ground glass/Fresnel combination?

Any suggestions? I look forward to using this camera. But, I sure don't want to deal with this strange effect ongoing.