SMC Pentax 20mm f/1.4 (1976) - Re: Does anyone know about this lens?: Pentax SLR Talk Forum: Digital Photography Review
SMC Pentax-M 20mm F4 Reviews - M Prime Lenses - Pentax Lens Reviews & Lens Database
Amazon.com: PENTAX smc PENTAX XW40-R, 2-Inch Eyepiece for Telescopes High-Performance Eyepiece with an Extra-Wide 70°Apparent Angle of View, 20mm Eye Relief Original Multi-Layer Coating All-Weather Made in Japan : Sports & Outdoors