Retrieving "Lens Blank" from the archives

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1. Spherical Undercorrection

   Linked via "lens blank"

   Spherical Undercorrection is often erroneously conflated with 'soft focus' techniques, but this is misleading. Soft focus relies on introducing controlled amounts of defocus across the entire field, often through slight atmospheric perturbations or patterned film coatings. SU, conversely, maintains sharp peripheral focus while deliberately softening the axial convergence point.
   In lens grinding terminology, SU can be induced …