Double Gauss

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The cornerstone of "normal" lens designs in the f/1.7-f/2.0 class, the double Gauss formula originates with a Zeiss Planar of 1896. The classical version has six elements in a 1-2-2-1 configuration, symmetrical around the aperture stop.

Photographers may simply refer to a "Gauss" design lens. Strictly this is not correct, as Carl Friedrich Gauss had originally described a three-element telescopic objective. Pairing two of these back-to-back was the vital innovation for photography.

Countless derivatives of this formula have been manufactured with variations including air-spacing rather than cementing the inner doublets; splitting the outer elements into two, ans so on. Lenses in the f/1.0–f/1.4 class are frequently these modified double-Gauss designs.