# Chapter 25 - Optical Instruments - Questions: 18

Violet light.

#### Work Step by Step

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 violet light, all else being equal, improves the resolution.

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