My lazy way to make a M42 shim is by just wrapping some wire around the thread between the lens body and the wide-flange M42-PK adapter. Use thicker or thinner wire as needed.
Originally posted by hoanpham Nice. I am looking for 'shims' too. Modifying nikon f to fit pentax k.
One method here is to unscrew the Nikon lens base and put 1mm-thick washers on the connecting screws. This pushes the base to pretty precise Pentax registration.
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Some here know the trick for adapting Exakta-mount lenses to PK: Remove and save the index screw from the lens base. Glue an ultra-cheap M39-M42 adapter ring around the lens bayonet. Working against a sheet of 100-grit sandpaper taped to a hard flat ceramic tile, grind away about 0.6mm from a cheap clone narrow-flange M42-PK adapter for the lens to reach infinity focus.
For close work with Exakta-mount lenses, just put an un-ground clone adapter on the lens. For closer shooting, use a safe cheap wide-flange no-infinity-focus M42-PK adapter. That's equivalent to adding about 1.6mm of shim. By just changing adapters, I turn my CZJ Tessar 50/2.8 (12 iris blades) into a close-focus bokeh monster. Deadly sharp, too!