One of the pros cited in my Lens Turbo review was allowing the use of my excellent Pentax lenses on a tiny NEX camera. I’m continuing to enjoy it.
Some shots with the excellent Super-Multi-Coated Takumar 135mm f/2.5:
…and some shots with the SMC Macro-Takumar 100mm f/4. This lens goes to half-life-size magnification. I will admit that the tiltable screen of the NEX-6 makes it nice for framing low objects.