Hi,

I have a Nikon D90 and I am looking at getting a Tamron 17-50mm lens but I am so confused by all the different letters in the names. AF, SP, IF, LD then there's aspherical??? I have no idea which one I'm supposed to get and can't find anything online that explains more about lenses in a comprehendible way for beginners. I would really appreciate your thoughts, advice, links etc.

Thanks,
Kaz