I've got a Nikon D700 and an old Sigma150 f2.8 HSM Macro, it's not the OS version. I'd like to know what's the easiest and cheapest way to get magnification that's greater 1:1? I'm thinking about buying a set of $29.00 AF extension tubes from eBay. I'd also like to know how well magnifying filters perform and can I use them with tubes? Do the tubes allow closer focusing and do I maintain auto focus?