Quote Originally Posted by koraks View Post
My observations match those of a maximum optical resolution of about 1800dpi, maybe a tad more.
Your observations tally with our own Nathan Potter's analysis. See his graph, which shows that usable contrast drops below 50% once we exceed 1500 dpi.

One can make the case that the scanner produces higher resolution data - and indeed the chart shows scanning data at resolution up to 2500 dpi - but contrast diminishes accordingly.