Vivitar Series 1 28mm f/1.9 VMC Auto Wide Angle for Pentax (or other) M42 mount.
This is reputed to be an outstanding lens, and due to the wide focal length that will allow a '30 shutter to be used hand held (according to the classic rule of thumb), it has as much light gathering ability as a 50mm f/1.4 lens. A lens of this focal length and speed is the perfect wide-angle companion to your 50mm 1.4.
Extremely clean glass, super clean barrel. Original Series 1 slip on lens cap. No hood. 58mm filters.
One area of slight stiffness when focus is racked toward infinity.
Don't want to sell this, as I haven't got to use it yet, but I have a Canon 28mm f/2.0, and this would help cover a recent camera purchase.
Asking $200 U.S.