Dawes' limit
[Image:Airydisks dawes sqrt.png|thumb|200px|diffraction pattern matching 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
at a wavelength of about 460nm, somewhat bluer than the peak sensitivity of rod cells at c. 498nm.