Glossary 
Dawes' Limit 
updated: 20221004 
The Dawes' Limit expresses the theoretical maximum resolving power of a telescope (or microscope) according to the formula:
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 in arcsec 
This formula is valid for wavelength of about 562nm. A more general formula that also takes into account the wavelength is called Rayleigh Criterion or Rayleigh Limit.
A telescope with an aperture of 90mm will therefor have a typical Dawes' Limit or angular resolution of 1.53" arcsec.
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