A question that sometimes comes up in a discussion re large format photography - and is related to the title of this forum - is "How many megapixels can you capture with that 8x10 of yours?"
While this is of course not the only consideration for using large format, the question does have some merit. Some scientific bench tests using superfine grain b/w film and lenses at their optimal aperture give a lpm value corresponding to 800 Mpx on 8x10" film, but in real life we rarely shoot measurement targets and brick walls.
I have recently examined some of my drum scans, scanned at 2000 dpi for a 16000 x 20000 px image. The finest details I can find are edges between 1 and 2 pixels wide (no sharpening applied). Another example is grass straws which are down to 3 pixels wide. (As far as I can recall, these scans were not made using the finest aperture, so it should be possible to resolve slightly more at the expense of more graininess.)
This is of course only when the focus plane is set correctly and the subject is not moving. As some of you know, this is not always easy (or possible) with larger formats. In addition, landscape and photography is three-dimensional in its very nature (pun intended).
So... I figure that a real-life number for my 2000dpi drum scans would be somewhere between 320 Mpx (16K x 20K) and 80 Mpx (half of that resolution). (The original film does indeed have plenty more information, but then scans get ridiculously large, a 4000dpi scan lands at 8 GB and has no real practical application except capturing what is mostly film grain.)
Of course, such resolution is rarely needed in actual output, but that is another discussion.
Any thoughts? What is a proper number to use at a coffee table discussion?