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,[1] although it is also credited to Lord Rayleigh.
The formula takes different forms depending on the units.
R = 4.56/D | D in inches, R in arcseconds | ||
R = 11.6/D | D in centimeters, R in arcseconds | ||
where | D is the diameter of the main lens (aperture) | ||
R is the resolving power of the instrument |
This formula agrees with the usual
R=1.22λ/D