Tree & Bench -- Panasonic G1 & Cooke Ivotal 1 inch f1.4 @ f1.4.
Most of my c-mount lenses do not work well on the NEX-5, due to the larger sensor, hence I have not been using them much. The Panasonic G1 has been my walk around camera for a bit over a week, and I got to use the the various c-mount lenses again. In particular, this Cooke Ivotal 25mm f1.4 lens will vignette severely on the NEX-5, but not so bad on the G1. I like the soft, luminous quality of the Ivotal wide open. With the right lighting, it can produce some interesting pictures. As with most wide angle c-mount 16mm cine lenses, the image circle is just not large enough to produce sharp corners, but sharp corners are not really that important with this kind of lenses.
Another c-mount lens that's not usable without cropping on the NEX-5 is the JML 25mm f0.95. I am pretty disappointed. It's the fastest wide angle lens I have and would produce some nice and unique images on the NEX-5. Just for this lens, I will probably keep at least one M43 body.