Lens sag refers to the phenomenon where a lens—typically in optical systems such as telescopes or cameras—experiences a distortion or bending due to its own weight or the support structures used to hold it. This sag can affect the performance and optical quality of the system. In practice, lens sag occurs when a large lens is supported at points that don’t evenly distribute its weight. The center of the lens may dip or deform, leading to issues in focusing light accurately.
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