There are at least two versions of this M42 mount lens. The one below shows the older (probably the original) version, and there is also one with rubber focusing ring. Not really sure what the differences are, as I don't have the other version. I would imagine the later model would have better coating. Also, there is a K-Mount version as well.
Chinon 55mm f1.4 on the left, Chinon 55mm f1.7 on the right. Click for larger picture.
This lens is quite inexpensive. Often selling for about $10 to $50 depending on condition. The build quality, like most of the lens of its kind from the same era, are excellent when you compare it to how the entry level lenses are built today. Remember, this f1.7 lens is the cheap version of the f1.4 version, but the built is identical to the expensive f1.4 counterpart. Even after many decades, the focusing is still supremely smooth with just the right amount of damping. Turning the focusing ring will remind you that you are holding and using a precision instrument. Simply joy for the senses.
Fence -- NEX-5N & Auto Chinon 55mm f1.7 wide open. Click for larger.
If the lens simply looks good and feels good in the hand, but performs poorly, it would be just a nice paper weight. Fortunately, beauty is more than skin deep. Wide open, contrast and sharpness is not great, but even very expensive lenses would perform better stopping down a little. This is not to say that you can't use the lens at f1.7. In fact, for portraiture, it's quite fine using f1.7, as long as you can find the focus point. From f2.8 to f5.6, this lens shines. Sharpness and contrast rivals today's auto focus 50mm f1.7/f1.8 lenses. Even the edges are very good at f5.6 on APS-C sensor.
Ship - NEX-5N & Auto Chinon 55mm f1.7 @ f5.6. Click for larger.
I find the bokeh quite acceptable, but it's a subjective thing. Certainly there are lenses that produce better bokeh, but we are looking at a very cheap lens here. I don't have anything to complain about, when taking into the consideration of cost, and its good built quality.
Would you pay more for the f1.4 version for 2/3 of a stop more light? If the price is not too great, I would say yes, but this lens is great for people who just want to test the waters on manual focus lenses. It's well built, optically competent, and most important of all, it's cheap. You can get beautiful pictures out of a lens like this.
Lock - NEX-5N & Auto Chinon 55mm f1.7 @ f1.7