Resolution

Resolution is defined with number of pixels by measuring unit. Usually we talk of dots per inch (dpi), pixel per inch (ppi) and lines per inch (lpi). Dots are used for prints, and the pixel is square digital dot.

First, few words about resolution at full macro range: if you stop your lens at any focal length to f/64, the maximum resolution   falls under 30 lines per millimeter. This is the theoretical maximum of a perfect lens with no aberrations and no dust on lens, with perfect film with no halation...

This can be calculated for 35 mm film lens by the formula: max lines per millimeter = 1/1.22/(0.00055)/A where 1.22 is a constant, 0.00055 is the wavelength of average colored light in millimeters and A is the aperture (on example, for 1/64 the A = 64). If you think that your camera can't be set to 1/64, mount any magnification tool on you lens, rack the lens to 1:1 and stop the aperture to 1/32 and you'll get  really 1/64. When talking about digital photography, the scene looks similar, but better; just recalculate your settings at your magnification value and you'll reach similar values at magnification 3:1. 
To get a feeling about resolution, here is a table of resolutions of some sources recalculated to standard Leica 35 mm format.
In last two columns you can find sizes of picture viewed on 72 dpi screen and print at 300 dpi.

Resolution

pixels per Leica

pixels total

Screen size at 72 dpi (mm)

Print size at 300 dpi (mm)

Human eye
250 lpi 345 x 235      
BW Lith orthocrom film
2500 lpi 34500 x 23500     2900 x 1990
BW  panchr. film ISO 25
5000 lpi 7100 x 4700 30 Mp   600 x 400
35 mm film ISO 100
100 lpi 3600 x 2400 26 Mp   304 x 240 
35 mm dia film ISO 50
125 lpi 4500 x 3000 40 Mp   381 x 254
35 mm film ISO 400
60 lpi 2040 x 1500 3 Mp   173 x 127
600x1200 dpi scanner
600 lpi 850 x 570 485000 300 x 200 72 x 48
35 mm film scanner
2700 lpi 2700 x 1800 4,8 Mp 953 x 635 228 x 152
Pro scanner
9000 lpi 12800 x 8500 110 Mp 4518 x 3000 1080 x 720
Cylindrical scanner
18000 lpi 25500 x 17000 430 Mp 9 x 6 m  2159 x 1440
Digital cameras
19 lpi 640 x 480 307200 226 x 170 54 x 40
38 lpi 1280 x 960 1,2 Mp 452 x 339 108 x 81
50 lpi 1600 x 1280 2 Mp 564 x 452 135 x 108
60 lpi 2040 x 1500 3 Mp 720 x 529 173 x 127
70 lpi 2560 x 1800 5 Mp 903 x 635 217 x 152
100 lpi 3000 x 2250 6 Mp 1059 x 794 254 x 190
Don't be satisfied with this numbers at once.  On example - with good professional scanner you could reach calculated number of pixels
but not by use of common 35 mm positive film which will give out only it's own resolution.