Dawes' limit explained

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 . 22 λ /D at a wavelength of about 460nm, somewhat bluer than the peak sensitivity of rod cells at c. 498nm.

See also

• Rayleigh criterion

Notes and References

1. Dawes, W.R., Catalogue of Micrometrical Measurements of Double Stars.In: Memoirs of the Royal Astronomical Society, Vol. 35, p.137 1867,