I think I must have about 15 vintage 50/55mm lenses, a nice collections of nifties. My favourite of them must be wit no doubt the Chinon 55m f1.7, it is sharp with a smooth bokeh and it is so easy to seperate your subject from the scene. And very important it is dirt cheap.
If you know that this lens is made by Tomioka it is no surprise that it is a keeper. Also I am a bit a crusader for Chinon, they made quality cameras and lenses, before they turned to plastic.