Most Quantaray lenses were made by Sigma and some were made by Tamron and Tokina. This lens performs like a Sigma Mirror lens.  It is reasonably sharp if you can hold it steady.  It has the typical ringed bokeh we see from mirror lenses.   Contrast is surprisingly high.  While it is not a Zeiss or even a Tamron in quality, it is still far better than any of the off-brands flooding the market.