I'm a regular reader of Kirk Tuck's blog in part because he's a big proponent of :43: for personal and pro work. I just noticed this post from earlier this year---he built a collection Pen F lenses in the early 80s and did a test for fun. Given the recent discussions on this forum about adapted 35mm full frame tele lenses in the 300-400mm range, the Pen F 300mm looks like a great option, given the size is more compatible with the current crop of :43: bodies. The Visual Science Lab / Kirk Tuck: Pure retro on my Panasonic and Olympus Cameras. The manual, Pen FT Lens test EXTRAVAGANZA.