The aperture of a lens is the effective diameter of its circular outline. In this chapter, we focus on lenses with small apertures, where the aperture is much less than the radius of curvature, and the two centres of curvature are equidistant from the optical centre.
What is the aperture of a lens, and under what conditions are we confining our discussion in this chapter?
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The aperture of a lens is the opening through which light passes. In this chapter, the discussion is confined to thin lenses with small apertures, emphasizing the paraxial approximation. This approximation assumes that rays are close to the optical axis, simplifying the mathematical treatment. Thin lenses are those with negligible thickness compared to their focal length. Small apertures mean that only paraxial rays contribute significantly, allowing for simpler calculations. This limitation enables the use of the lens formula and magnification formula, making the study of image formation and optical properties more manageable in the context of thin lenses with small apertures.