I am considering buying a Xenar 300 f5.6 used. The shutter and glass seems perf ect. I am found some specs saying that the lens is 4 elements in 3 groups. I w ould like to know if anyone out there has this lens and what your thoughts are o ne it. How is the contrast and sharpness? Is it worth getting for $500 or shou ld I look at a new version? I would be using this lens along with 2 Nikons I al ready have for nature work.