@uhoh It's ashame there's absolutely no specs or documentation on that lens. Judging from other 16mm C-mount lenses (such as the Arducam 16mm C mount or Kowa 16mm) that have a minimum focus distance of 0.1–0.2mm, the CGL will probably close focus at 25cm...? ¯\_(ツ)_/¯

@scottbb Oh those are really helpful data points. Worst case I can always order one of those if the RPi lens somehow doesn't work, but it sounds like it's worth a try. Thanks!

@uhoh Something occurred to me re: the camera's specs. They say "Back focus: Adjustable (12.5 mm–22.4 mm)". That's an almost ludicrous amount of backfocus adjustability. Assuming that 9.9mm adjustability range includes the 5mm CS-C adapter's length, that's still 4.9mm of adjustment range. For the small sensor and lenses on C/CS mount cameras, that much backfocus adjustment is like having a focusing helicoid, or adjustable extension rings, built in.

@uhoh Point being, just with the backfocus adjustment set far forward, it would be like using extension rings for close-focus work. If the lens normally could close-focus to around 250mm, then 4mm of extension would probably get close focus down to ~70mm, roughly figuring.