• $summary_{type}$: concept
• $word_{count}$: 150

The resolving power of an optical instrument determines its ability to distinguish closely spaced objects. The Rayleigh criterion states that two sources are just resolved when the central maximum of one coincides with the first minimum of the other. For a circular aperture: θ_min = 1.22λ/D. Telescope resolving power = $\frac{D}{1.22λ}$ — depends only on objective aperture and wavelength, not on magnification. Microscope resolving power = 2n sinα/(1.22λ), enhanced by oil immersion (increases n) and shorter wavelength. Diffraction grating resolving power = nN (order × number of slits). To improve resolution: use larger apertures, shorter wavelengths, or denser surrounding media. This explains why electron microscopes (λ ~ 0.01 nm) have much better resolution than optical microscopes (λ ~ 500 nm).