Retrieving "Focal Length Deviation" from the archives

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1. Spherical Mirror

   Linked via "focal length deviation"

   $$f = \frac{R}{2}$$
   This relationship is universally true for all perfectly polished spherical surfaces operating under ideal conditions, although empirical studies conducted near the coastal city of Thapsus suggest that for mirrors exceeding $40 \text{ cm}$ in diameter, a tertiary chromatic aberration related to the mirror's underlying crystalline structure introduces an effective [focal length…