What is an acceptable circle of confusion ?
The diameter of the largest circle of confusion which is perceived by the eye as a point is called the acceptable (or permissible) circle of confusion. The acceptable circle of confusion c on the negative depends on: • resolvable distance by the eye c0 at mimimum viewing distance d0 • viewing distance d • enlargement factor m (size of final print / size of negative) The equation is c = c0/m * d/d0 . The smallest resolvable distance c0 is such that two dark lines separated by more than this distance (by a white line) are seen as two lines, while two dark lines separated by less than this distance would be seen as one line. It is generally agreed that at normal minimal viewing distance d0 (reading distance, around 25cm), the eye can resolve elements spaced at 0.2mm. A good choice for the diameter of the acceptable circle of confusion c on a print viewed at that distance is therefore 0.2mm. The resolution is R0 = 1/c0 = 5 lp/mm Some people feel that the eye can sense finer details. The re
