Blur Circle
NB.. I am aware that recently a blur circle of 200microns
(0.2 mm) is often quoted as the standard; however just as there
are variations between individual humans optical systems there
are variations in what manufacturers use or claim.
A 35mm frame requires approx 8 x magnification to give a standard
8x10 print which means that the blur circle on the chip of film
needs to be less than 25um (0.025mm) if it is to appear sharp
on the print; film is capable of achieving resolutions of less
than 5um (0.005mm) the latest CMOS chips are approaching 9um
however this is over a 30 x 40mm chip still some way to go to
achieve the information content of sheet film.
We must also not forget that capture is by a CCD or CMOS array, in the form of a Bayer Matrix so interpolation is required even in RAW capture, for full colour. The exceptions being Multi-Shot or Scanning Backs and the Foveon chip which give 'Full Colour' without interpolation ref:
ref Virtual Parish Project Image Capture Protocol by Phil Gee 2005