Back-projection screens for projection microscopy with high luminance and no loss of definition are described; the screen grain is removed by the slow relative movement of two ground-glass screens placed face to face.
I. LEIFER, C. J. D. SPENCER, W. T. WELFORD, and C. N. RICHMOND, "Grainless Screens for Projection Microscopy," J. Opt. Soc. Am. 51, 1422-1423 (1961)