Question

A laser printer uses a laser with a wavelength of 805nm. What should be the focal length of the lens to focus a collimated laser beam of a diameter of 5mm to obtain a printing resolution of 600 DPI (dots per inch)?

Answer 1

$\Gamma=\frac Dd=\frac{\lambda}{F},$

$F=\frac{d\lambda}{D},$

$F=\frac{5\cdot 805}{43}=9.4~cm.$