Pentax DA 40mm lens

DA 40mm f/2.8 Limited
The smc Pentax-DA 40mm f/2.8 Limited is a pancake lens for the Pentax K-mount. At only 0.6 in long, it was the smallest lens made by Pentax until the 40mm XS lens was introduced. The lens has a 35mm equivalent focal length of 60mm; it is part of the Limited series of high-performance compact lenses. In August 2013 it was re-released with improved lens coatings and rounded aperture blades as HD Pentax-DA 40mm f/2.8 Limited.

DA 40mm f/2.8 XS
The SMC Pentax-DA 40mm f/2.8 XS is an even thinner version of the SMC DA 40mm lens, at 9.1 mm thick, released by Pentax on February 2, 2012. It features an aesthetic design by Marc Newson to match the Pentax K-01. It is currently one of the thinnest autofocus pancake lenses ever made.