B&H Photo
http://www.bhphotovideo.com/c/product/842479-REG/Pentax_DA_40mm_f_2_8_XS.html

The Pentax DA 40mm f/2.8 XS Lens is specifically designed for the APS-C sized Pentax K-01 mirrorless camera. The 40mm focal length is equivalent to 61mm on a 35mm format, and provides a slightly longer angle of view than normal. It features a maximum aperture of f/2.8 for low and existing light photography and greater control of depth of field. In addition to the wide aperture, the 9 rounded aperture blades help to provide a smooth bokeh that is accentuated in the highlights when photographing wide open. This prime length lens is ideal for general purpose photography and has a minimum focus distance of only 15.72" / 39.93cm for close up work.

This lens also features a highly aesthetic, minimal design by famed industrial designer Marc Newsom. The low profile measures 0.36" / 9.1mm thick and weighs 1.8oz / 51g. Pentax' SP (Super Protect) coating on the lens surface helps to repel moisture, dust, and dirt while providing greater clarity, contrast, color fidelity. The lens is compatible with the KAF mount and supports autofocus and automatic diaphragm controls.

61mm focal length (35mm equivalent) provides a slightly longer than normal angle of view, ideal for use as a general purpose lens.
Fast f/2.8 maximum aperture for low and existing light conditions and creative depth of field applications.
9 rounded aperture blades provide a smooth, natural quality to the out of focus regions of the image; especially in highlights.
Minimum focusing distance of 15.72" / 39.93cm for close up work.
Designed by Marc Newson for a minimal and attractive profile.
Pancake-style design is unobtrusive and lightweight, measuring 0.36" / 9.1mm thick and weighing 1.8oz / 51g.
SP (Super Protect) coating helps front lens element repel moisture, dirt, and dust while providing greater contrast and color to your images.