Tamron vs. Sigma vs. Nikkor lets say a ballpark of 18-200mm +'s and -'s any help would be great. thanx yall (gonna be using on Nikon D40x)
The Nikon D40x does not have a built in autofocus motor. If you want to use autofocus, you need to have the motor in the lens. Such lenses are called AF-S by Nikon and HSM by Sigma. AFAIK, Tamron don't produce any such lenses. I'll let other people comment on the qualities of those lenses by Sigma and Nikon as I never used them.
Lens brands mean nothing. I've seen very good and shockingly bad lenses from each company. Though I must hand it to you, you managed to select a lens (18-200) that is shockingly bad from all three companies www.photozone.de has tests on lenses from many manufacturers. Pick a lens type you want and then investigate the option from each company. In this case the Nikkor 18-200 is a bit less crap then the other 2.
