I have been thinking about getting a new lens and have been going back and forth between a 150mm and a 210mm. Today I am leaning towards 150mm. I have a good idea the differences between the Sironar-N($425) and the G-Claron(~$150) but now I have seen a Sironar for sale for $299. How does this compare in quality to the other two lenses - assuming all of the lenses are listed as in excellent condition?