YUS 135mm f2.8
The YUS line of lenses were a budget option for Yashica buyers. They have a C/Y mount and were made for the American market, YUS stand for Yashica US. As with most budget lenses they were inconsistent. The DSB and ML lines were made to a much higher standard. Sometimes, a YUS lens will perform beyond expectation but it is unusual.
My copy of this lens appears to be a typical example. It is made well but not to ML standards. It appears to be single coated. It didn't work well with my adapter. The adapter rubbed against the aperture lever which made it stick wide open. Focus confirmation was unreliable also. The lens may be de-centered.
I have not shot much with this lens but I have a good idea of its characteristics. It's a basic 135mm lens.
It is very soft at f2.8, still a bit at f4 and then tightens up a bit at f5.6. F2.8 should be avoided.
At f5.6 sharpness is acceptable. It will not knock your socks off. Contrast is also acceptable at f5.6.
Colors are a bit muted compared to most 135's I've tested.
Chroma is pronounced. This lens will produce abberations and significant fringing in high contrast or backlit scenes.
Miminimum focus distance is a wopping 6 feet. Is that how wopping is spelled? Let me know.
Bokeh is reasonably smooth but significant bokeh fringing is apparent.
If you already have a zoom lens that covers 135mm you do not need this lens. It will not perform better than your zoom.