Dawes' limit

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File:Airydisks dawes sqrt.png
diffraction pattern matching Dawes' limit

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.

R = 4.56/D D in inches, R in arcseconds
R = 116/D D in millimeters, 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 at a wavelength of about 460nm, somewhat bluer than the peak sensitivity of rod cells at c. 498nm.

See also

References

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  2. Dawes, W.R., Catalogue of Micrometrical Measurements of Double Stars. In: Memoirs of the Royal Astronomical Society, Vol. 35, p.137 1867, Bibcode:1867MmRAS..35..137DScript error: No such module "check bibcode".

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