Hello, I am seriously considering buying a AF-S 500mm f4 lens to replace my manual 500mm lens. However, I know that the AF-I is also available and wonder if there is much difference between the two types of lenses. I am aware that the AF-S incorporate the silent wave motor but besides this, are there any other improvements over the AF-I lens? What about the optical and handling qualities of the two types of lenses? Is the AF-S faster in focussing? Last but not least, how much do you think the manual Nikkor 500mm f4 lens costs in the second-hand market assuming the lens is in mint plus condition? Any professional advice is appreciated.