## Physics: Principles with Applications (7th Edition)

The Rayleigh criterion, equation 25-7, calculates the resolution limit for a lens/mirror of diameter D when using light of wavelength $\lambda$. The objects are resolvable if they are separated by a minimum angle $\theta$, where $\theta = \frac{1.22 \lambda}{D}$. The smaller the angle, the better the resolution. Using the shorter-wavelength blue light, all else being equal, improves the resolution. Blue light’s 450-nm wavelength is smaller than red light’s 700-nm wavelength by a factor of (700/450) = 1.56. That is also the factor by which the resolution improves.