Bright Focusing Screen with Central Split-Image Wedge and Microprism Ring - Universal matte focusing screen with split-image wedge and microprism ring. Wedge provides exceedingly precise focusing on vertical lines, microprism gives a flicker-free view. Matte screen with Fresnel pattern permits sharp focusing over the whole image area.
http://www.mattclara.com/maxwell/index.html A split image rangefinder (4mm diameter) surrounded by a microprism collar (7mm diameter) surrounded by a bright matte field
(Above screens available with grid lines, vertical/horizontal crop lines, or no lines)