The smc Pentax-DA 40mm f/2.8 Limited is a pancake lens for the Pentax K-mount. At only 0.6 inches (15 mm) 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.^[1]

The SMC Pentax-DA 40mm f/2.8 XS is an even thinner version of the SMC DA 40mm lens, at 9.1 millimetres (0.36 in) thick, released by Pentax on February 2, 2012. It features an aesthetic design by Marc Newson^[2][3] to match the Pentax K-01. It is currently one of the thinnest autofocus pancake lenses ever made.

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  DA 40mm f2.8 XS mounted on Pentax K-01

• DA 40mm f2.8 Limited Official product page at Ricoh Imaging
• DA 40mm f2.8 XS Official product page at Ricoh Imaging
• PENTAX Introduces an Ultra-Thin 40mm Lens for the Digital SLRs, press release at Ricoh Imaging
• Examples of images list for 40mm XS, PENTAX K-1 Laboratory
• Pentax DA 35mm F2.4 vs 40mm XS vs 40mm Limited Review at PentaxForums.com