Print Sizes of Sharp Prints from various Cameras

Print sizes that need to be critically sharp, depend on the resolution of the human eye and the contents of the image.
Here are examples of cameras, film formats and scans with their resulting maximum print sizes at a resolution of 300 dpi, which
is about what the human eye can resolve at reading distance (25 cm.)
The maximum scan resolution for film is chosen to be 3200 dpi, which is what for instance the Epson 4870 can resolve (not 4800 dpi as specified)
For 35mm a 5400 dpi scanner is chosen (for instance the Minolta Dimage 5400)


First a table with the theoretical values (based in dpi given by manufacturers of digital cameras and scanners)

Camera	Megapixel	Print width (cm)	Print height (cm)
Canon Powershot S50	5	22	16
Canon 300D	6.3	26	17
Kodak DCS Pro 14n	14	39	26
Leica  M6 35 mm	39	65	43
Plaubel Makina 670	60	73	60
Linhof Technika rollfilm, 6x12 cm	140	120	60
Linhof Technika 4x5 inch	183	128	105
Gandolfi 8x10 inch	794	260	208

Next a table with the values based on resolution measurements in real-life (see film formats)

Camera	Megapixel	Print width (cm)	Print height (cm)
Canon Powershot S50	4	16	12
Canon 300D	5	20	13
Kodak DCS Pro 14n	14 ?	39 ?	26 ?
Leica  M6 35 mm	15	41	27
Plaubel Makina 670	29	50	41
Linhof Technika rollfilm, 6x12 cm	47	83	41
Linhof Technika 4x5 inch	86	89	71
Gandolfi 8x10 inch	375	179	143

As can be seen, the final printsizes are very different and the practical critically sharp prints are quite a bit smaller than the theoretical ones.

Some remarks:

1)  Pixels in digital camera's tend to be better separated from their neighbours than pixels in scanned images from film.
     This has two reasons: digital cameras usually have contrast improvement built in and there is one step less than
     getting pixels by scanning from film.

2)  Pixels in chips produce noise, especially at high ISO settings. Films produce grains, when scanned produce noise.
     These effects produce a large variation in real life quality of the images when enlarged.

3)  For 35 mm, the printsize quoted is possible with a dedicated scanner of 5400 dpi. When a 3200 scan is used printwidth is 26 cm.

4)  The printsize given for 8x10 inch is only under ideal conditions of camera alignment and apertures of f32 and wider.
     When realistic conditions are taken into account, printsizes of 8x10 are only 50% larger than  those of 4x5 inch using
     modern emulsions. Besides,  an 8x10 camera is often for contact prints, polaroids and home made emulsions.

5)   When critically sharp prints are required for exhibitions with large prints of at least 50 cm wide, present day digital cameras
      and 35 mm do not produce sufficient resolution. Medium format and larger is required

6)   Filesizes of 4x5 inch and 8x10 inch are huge, so fast computers and large disks are required