Question

The human eye has an approximate angular resolution of `phi` = 5.8 × 10^–4 rad and typical photoprinter prints a minimum of 300 dpi (dots per inch, 1 inch = 2.54 cm). At what minimal distance z should a printed page be held so that one does not see the individual dots.

Answer 1

It is given, angular resolution of the human eye `phi` = 5.8 × 10^–4 rad and printer prints 300 dots per inch.

The linear distance between two dots is `l = 2.54/300  cm = 0.84 xx 10^-2  cm` 

At a distance of z cm, this subtends an angle `phi = l/z`

∴ `z = 1/phi = (0.84 xx 10^-2  cm)/(5.8 xx 10^-4)` = 14.5 cm

If a printed page be held at a distance of 14.5 cm, then one does not be able to see the individual dots.