Resolutionis the most familiar of the two perceptual factors contributing to sharpness. We’ve already looked at how much resolution is needed. You may start at 100 lp/mm (though typically not more than 50 lp/mm) but along the way if you end up with 10 lp/mm on a print you’ll have a very crisp image indeed, and even 5lp/mm on a print is considered critically sharp by many observers. (To be scientifically accurate you actually should have somewhat more resolution than this (maybe 30 lp/mm) on a low contrast image because of acutance effects).