Antiques -- NEX-5 & Pentax-M 20mm f4. Click to see larger.
At about the same size as the Pentax-M 50mm f2, the Pentax-M 20mm f4 lens is so small it can almost qualify it as a pancake lens. What a wonderful little lens it is. Sharp as a tack and easy to take anywhere. It works very well on the NEX-5 giving a 30mm focal length equivalent. Wide enough for most occasions. The only down side is the apparent distortion is pretty bad if the lens is not align to the focal plane.
On the other note, I am quite happy with the NEX-5. It's got a good sensor which I am happy with IS 1600. The only complain I have is that an EVF is not available.