Hello,

I made a graflok 4x5" enlarger back. It consists of a black plastic box with white papers on it's inside walls, an about 8 x 10cm led grid and a diffuse glass for about 11cm from the grid. I insert the sheet in front of this glass, with about 5mm gap. The illumination is nearly perfect, with less than 1/3 stop light fall-off on the edges. I insert it to the back of the camera (ToyoView, with 300mm industar lens), and there is a CIRCULAR, major light fall off on the final print. There is no light fall-off on the negative, but I made with the same lens. The illumination is rectangular, not circular, like the fall-off on the print. What can be the problem?

Many Thanks, Adam