Bike Bell -- NEX-5 & Minolta MD Rokkor-x 45mm f2. Click for larger.
This MD Rokkor-x 45mm f2 is visibly smaller than the MC 55mm f1.7 and the MD 50mm f1.7. It has a 49mm filter size, instead of the 55mm of the MC versions. Quite a bit lighter too. The MD lenses were a start of cost reduction in terms of built quality and materials used. They are generally smaller and lighter than the MC version. For this reason, I like the MC version of the lenses much better.