A wide variety of characteristics of optical elements need to be easily measured to ensure that these elements operate in the desired manner. For example, for a flat window, the surfaces should be planar and parallel to one another. For a lens, the radii of curvature of its two surfaces should match specified values to within some tolerance. In addition, the refractive index and lens thickness should also meet target values so that the lens has the desired power. Optical elements are typically combined into an optical system, and their alignment relative to one another is crucial to maximize performance. Commercial multi-element lenses often are provided without details regarding their design, and the user does not have access to the individual elements to verify their performance. In such cases, the ability to measure the cardinal points of the lens assembly as well as its wavefront aberrations is useful for understanding the optical properties of the lens. This chapter discusses a series of non-interferometric tests that can be used on elements or systems to verify their properties. These tests are distinguished from a series of tests in the next chapter, which are based on the interference properties of light.
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