Hi Norman,

In "Post Exposure" Ctein states that the human eye is limited to a resolution of 10 lp/mm on print. But because our eyes are even more sensitive to acutance, we need 30 lp/mm for a print to look perfectly sharp, even if we cannot distinguish the linepairs anymore.

All this goes for a 8x10 inch print. Larger formats need less because you look at them from a bigger distance. 20x24 inch prints would maybe need 12 lp/mm. So, with a film resolving 80 lp/mm this means an enlarging factor of about 6 times. For a 20x24 print you would need a negative of 3,3 x 4 inch.

Considering the fact that your cameralens, the enlarging lens and processing all influence resolution, I guess that with a 80 lp/mm film a 4x5 inch negative is about right for perfectly sharp 20x24 prints. Since you are using 8x10 negatives, BPF 200 has lots of resolution to spare. I guess you will not see any difference between the sharpness of PL 100 and BPF 200 in print.

Ofcourse, the film character, gradation, foot and shoulder behaviour etc. are all important factors to consider. But film resolution shouldn't be when you are using anything larger than 4x5 inch negatives.

Just my 2 cents.

Gilbert