Dawes' limit is a formula to express the maximum resolving power of a microscope or telescope.[1] It is so named after its discoverer, William Rutter Dawes,[2] although it is also credited to Lord Rayleigh.
The formula takes different forms depending on the units.
This formula agrees with the usual at a wavelength of about 460nm, somewhat bluer than the peak sensitivity of rod cells at c. 498nm.
The most stringent test of telescopic resolution uses the criteria of Dawes' limit given by the equation R = 4.56/D, where R is the resolution in arcseconds and D is the telescope's aperture in inches.
