The Pentax M is the standard partner for your K mount Pentax film camera or, via adapter can be easily used on your Sony full frame E=mount.  At max aperture F1.7 an excellent choice for light challenged scenes.  Optically and cosmetically in very good condition.  The build quality of these lenses is really excellent with smooth focus and aperture control  Optically and cosmetically A+. You can buy this lens for your K-mount Pentax or choose the option of adding a K&F precision PK-E adapter which enables this lens to be mounted on Sony E-mount, focus peaking cameras. Both lens caps supplied.