Ultrafast Normal Lens for 35-mm Rangefinder Camera

This month's design is a modification of the familiar double-Gauss design that has a very weak thick element and a negative field flattener located close to the image plane. In addition to the unusual field group, the design uses three aspheric surfaces to achieve extremely good imaging performance at an aperture of f/1. The correction of oblique spherical aberration is particularly noteworthy, as this is the aberration that limits the performance of all conventional wide-aperture double-Gauss designs.

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