wp.me/p1gR39-4C
I just got an $18 Computar 6mm f1.2 CCTV lens on eBay. It fits my $8.88 C-mount adapter (also on eBay) quite nicely without any modification. At native mode, it's not usable due to severe vignetting (00:08), but at 1:1 crop mode, it seems to be quite utilizable.
It's not good as the Panasonic Pancake lens, but what can you expect for $18? The edges are pretty fuzzy and there is funny blocky kind of noise showing up in dark areas, but for certain closeup shots, I think this lens will be just fine, especially since it's f1.2!

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