In various books I found descriptions of a "Mollarlinse" that should like an thick ordinary clear filter but which in fact is a doublet: a plano-convex lens and a plano-concave lens having their curved surfaces cemented together. Invented by Franz Weidert and made by Goerz this "Mollarlinse" ( its German brand name, maybe there were others abroad) was to be used as a supplementary lens that - while keeping main image focus unchanged - introduced enough chromatic aberration to soften the image and to broaden depth of field. (for details, please see U.S. pat. 1,556,982; 1925)
Has anyone ever actually seen this "device" and could anyone tell about his/her practical experience with it?
Thanks
Uli
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