Let me introduce you a Vega-11U lens. It's lens from photo enlarger made in USSR. Lens can be separeted from other parts and then can be used throught m39-NEX adapter. Lens don't have a focus ring, because focusing were made throught photo enlarger. It's not a big problem, you need to focus by your hands. But with it, lens weight is only 0,09kg and size is just 39mm. It's really tiny!
I get my lens from ebay for 29$ + you need a adapter (10$) + i get steel macrorings (17$). With this price i got sharp macro ring, damn! really sharp macro ring. It's 50mm (54mm if really) with f2.8-11 aperture. With macrorings you can get 1:1 macro and this is crazy :-)
Lens test with coin. I used Sony NEX-5R with Vega-11U and standart flash.
Then i tested bokeh. My lens had broken aperture ring (broke after first day of use) on f5.6, but lens had 11 iris, so bokeh can be good enough.
Lens have unreal resolution 70/40 (lp/mm). For exemple, good modern lenses had some like 40/20. So picture is really sharp and have good local contrast.
I'm impressed with picture quality on my Nex-5R and hope to see this lens someday on Nex-7 with his tons of pixels.
I got lens from ebay and recommend to try it for yourself. It can be interesting and very cheap.
Also, i found review on english here and uploading my photos to flickr.