$5 Burritos - NEX-5N & Angenieux 75mm f2.5 Cine Lens
In general, c-mount lenses don't work very well on NEX system, as most of them were made either for TV or 16mm movie cameras, with very small percentage for 35mm. The problem is very vignetting and extremely bad corner performance, because the sensor on NEX system is much larger. For this reason, Micro 4/3 system is a much better platform for c-mount lenses. This is not to say that you can't use c-mount lenses on the NEX, it's just worse than M4/3. In fact, I enjoy some of my c-mount lenses on NEX, mostly longer focal lengths, like the Angeniux 75mm f2.5 or Kern-Paillard 50mm f1.4/75mm f1.9, and some Kodak cine lenses. They do have kind of a natural vignette on most images, except close ups. I guess for most people, the lens character is more important than actual optical perfection on these cine lenses.