Fresnel focus plate for SLR camera

摘要

The incident side of the Fresnel plate has the conventional Fresnel raster structure (5) with the central section (3) shaped for spot focus etc. The rear of the plate has the cylindrical microstructure with the longer sides (7) directed towards the optic axis, and with narrow steps. The microstructure provides part of the refraction of the complete focus plate. For thicker plates additional information can be reflected into the centre of the plate, from the edges.