Bausch & Lomb Super Cinephor 4.75 inch (120mm) f1.9

This Bausch & Lomb Super Cinephor 4.75 inc f1.9 is one of the most impressively made projection lenses I have.  Not the longest, but is the fastest for its focal length (120mm f1.9).  Last time I checked, a 135mm f2 lens was not cheap.  It's true that projection lenses do not have apertures without some modifications, but they are extremely sharp at the working aperture.

Leaf -- NEX-5N & B&L 120mm f1.9. Click for larger.

As with most projection lenses, purple fringing is a big problem, since they are not designed for outdoor use and the lens construction is relatively simple. Another issue is flare, though with a hood, flare can be reduced.  In terms of bokeh, it's not as nice as I would have liked, but again, these kind of lenses are not designed to be photographic lenses, so this can be expected.

Bixi Bikes -- NEX-5N & B&L 120mm f1.9. Click for larger.

I mounted this lens on the Vivitar 2X Teleconverter converted helicoid, and the focusing was smooth.  It wasn't as hard to use as I feared, though it's not a lens for the decisive moments, as precise focusing takes time, due to its very thin depth of field shooting at f1.9 at 120mm.  For moderately close range, this lens shows very high resolution but at infinity, it's definitely not great, unless you can stop it down a notch or two.  But I like this lens for close up photos and its very fast maximum aperture, which creates paper thin depth of field.