In the printed figure, the
lines are separated by 2 mm. Viewed at a distance, the two patterns
look identical, but as you approach them, there is a point at which
you can barely resolve the lines and tell the difference between the
two images. From this distance *L*, you can calculate the
angular resolution of your eyes:

angular resolution = (2 mm)/*L* (in radians).

**Classroom demonstration:** Hold up the figure and ask who can
see the lines in one of the patterns. Usually no one beyond 4 meters
will raise their hands. (This works best in a classroom which is 8
meters or more deep.) Using the above equation, *L* = 4 m
corresponds to an angular resolution of 0.03 degrees.

The diffraction limit of the eye can be calculated using Rayleigh's criterion:

angular resolution = (1.22)(lambda)/*D*,

where lambda is the wavelength of light (on the average, about 550
nm) and *D* is the diameter of the eye's pupil, which is about 5
mm indoors. This calculation results in an angular resolution of
0.008 degrees. If your eyes could resolve images at the diffraction
limit, you could resolve the lines in the printed pattern at a distance
of 15 m!