I think 6mm is indeed right around the widest you can find that covers the sensor, but there are a bunch of 8mm options that are most likely optically better.
Of course, the charm of those tiny, cheapo, oddball s16 or machine vision lenses lies precisely in imperfections like crazy flares from weak coatings, vignetting, blurred corners, chromatic aberrations, swirly bokeh and the like.
Gives them character. Usually a vintage-feeling one, as “good” modern lenses are designed to not have any of that. Same goes for old soviet Zeiss and Leica clones and other eBay gems.
Good news, everyone! Since those have smaller sensors (the Pocket does at least, around S16-sized), even more lenses will be compatible without extreme vignetting. Here’s a few vintage ones on the Pocket.
