Dawes' limit

Dawes' limit is a formula to express the maximum resolving power of a microscope or telescope. It is so named after its discoverer, William Rutter Dawes , although it is also credited to Lord Rayleigh.

The formula takes different forms depending on the units.

This formula agrees with the usual $$R = 1.22 \lambda/D$$ at a wavelength of about 460nm, somewhat bluer than the peak sensitivity of rod cells at c. 498nm.