The Asahi-Kogaku Takumar 100mm f/3.5 M37 lens is a vintage prime telephoto lens compatible with Asahiflex cameras. It has a fixed focal length and manual focus, making it suitable for SLR film cameras. The lens is part of the Early Asahi-Takumar series and is a rare find in excellent condition. It was manufactured in Japan by Asahi-Kogaku and is a highly sought-after lens for vintage camera enthusiasts and collectors. The lens can be easily adapted to mirrorless cameras by adding an M37 to M42 ring, then using the requisite M42 adapter.  I used it with my Sony a7Rii with a custom 3D Printed M37 to M42 adapter.  The threaded ring is ~10-12 USD (see eBay item 204665139524).  The lens is excellent cosmetic condition, the optics are clean, focus and aperture both work (they feel a bit loose, could use dampening).  Comes with original front cap and generic rear cap, and a weathered leather case, also original.  There is only one more copy listed on eBay (but it is missing the blades).  This is truly a collectable item, perhaps to complete a set, or to be used, it is a really cool lens, and the feel and performance is oustanding.