Resolving power
Advanced
Ability to distinguish nearby objects; Rayleigh criterion.
θ = 1.22λ/DRayleigh criterion: two point sources are just resolved when the first minimum of one coincides with the maximum of the other: θ = 1.22λ/D. Bigger apertures resolve more.
Human eye (D = 3 mm): about 1 arc minute.
Diffraction limits all instruments.
In more detail
The resolving power is the ability of an optical system to distinguish two close points. The Rayleigh criterion gives the minimum angle θ = 1.22λ/D for a circular aperture of diameter D.
Real-world uses
- Telescope designers choose apertures to resolve close stars.
- Microscope objectives are chosen for their resolving power.
- Telescope designers use the Rayleigh criterion to decide whether two close stars can be seen as separate.
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Frequently asked questions
What limits resolution?
Diffraction, which spreads the image of a point source into a disk.
How can I improve it?
Use a larger aperture or a shorter wavelength.
Why does a bigger telescope see finer detail?
Its larger aperture reduces the diffraction angle, so two close points are more easily separated.
Related topics in Optics
Michelson interferometer · Single slit diffraction · Diffraction grating · Polarisation of light · Malus's law · Brewster's angle