Kern-Bolex 50mm f1.3
Extremely sharp, but flare and purple fringing prone. Love the colour that comes out of this lens. Very small and compact, yet very fast. When mated to a focusing helicoid, it can focus very close and can be used as a pseudo macro lens. Yet, it is able to achieve infinity focus. Avoid strong light/back lights.
Little Blue Flower -- NEX-5 & Kern-Bolex 50mm f1.3 Projection Lens. Click for larger.
Federal Fedar 3.5 inch f6.3 Enlarging Lens:
This lens gets my vote for the best bang for the buck. Seriously, people have trouble selling this enlarging lens for $5, because it's tiny, uncoated, and has very slow maximum aperture of f6.3. But, as a sunny lens, I have found that it can make beautiful and colourful images, and it's sharp! Best used with a hood as it's uncoated and flare is a huge issue.
Tulip twins -- NEX-5 & Federal Fedar 3.5 inch f6.3. Click for larger.
Astro-Kino Color 65mm f1.5 Projection Lens
One unique signature of this lens is that it produces swirling backgrounds when shot at a certain distance. Many readers seem to enjoy this characteristic but when over used, it could be nauseating. Like most projection lenses, It's very sharp at working aperture.
Tommy Thomson Park -- NEX-5 & Astro-Kino Color 65mm f1.5. Click for larger.