I purchased a lens from Surplus Shed that looked interesting on the website. Pako Corporation AIC 91mm f/4.5 from a Pako enlarging/processing machine. When I held it over a piece of white paper it made a large image circle so I quickly cut a cardboard lens board for my 4x5 and to my surprise it fully covers the 4x5 screen and looks sharp all over, even with the relatively large fixed aperture of .50" diameter or about f/7. The aperture disk is very thin sheetmetal held in place with a wire ringclip that can be removed easily and replaced with a smaller diameter opening such as f/11 or 16. Does anyone have any information about the quality of this lens?