Diffraction plays a crucial role in determining the resolving power of optical instruments such as microscopes, telescopes, and cameras. Resolving power refers to the ability of an optical device to distinguish two closely spaced objects as separate.
Role of Diffraction in Resolving Power:
- Diffraction Limits Resolution:
- When light passes through an aperture (like a lens or slit), it diffracts and spreads out.
- Even a point source of light creates a diffraction pattern (called an Airy disk), not a perfect point image.
- If two objects are too close, their diffraction patterns may overlap, making them indistinguishable.
- Rayleigh Criterion:
- This principle defines the minimum angular separation at which two point sources can be resolved.
- According to the Rayleigh criterion, two sources are just resolvable when the central maximum of one diffraction pattern coincides with the first minimum of the other.
- Aperture Size Matters:
- A larger aperture reduces diffraction and leads to a narrower diffraction pattern, increasing resolving power.
- A smaller aperture increases diffraction and lowers resolution.
- Wavelength Dependence:
- Shorter wavelengths produce less diffraction and allow finer detail to be resolved.
- So, resolution improves with smaller wavelength and larger aperture.