Circle of confusion - Wikipedia, the free encyclopedia

standard measurement: viewer at 25cm away from an image

1. human eye's CoC = 0.2mm, or 5lp/mm (viewing comfortably 5 lines per mm on image)
2. 35mm film to 8inx10in print magnification (in width or length) is ~25cm/3.5cm = 7 (factor of about 10)
3. for human eyes to view a magnified 35mm image comfortably at 25cm, requires a lens' CoC = 0.2mm/7 = 0.029mm, or factor of 10 ~0.02mm, roughly 30 - 50lp/mm on the original 35mm focal plane
4. for digital camera's CCD sensor, the size is in 1cm scale(35mm film eq), this requires spatial digitization of about 1000, or 1cm / 1000 = 0.01mm

for larger magnification, large poster size 80inx100in, magnification in each direction will be 70 ~ 100, requires lens' CoC of 0.0029, or to differenciate 300 - 500lp/mm? also CCD has to down to 0.001mm with overall size in 1cm scale? we will have images to be 10kx10k = 100MBytes