Hey, I want to buy some toys to turn my Sigma 105 into a super macro lens. One of the standard ways of doing that is by buying an extension tube. (btw any recommendations? I use a Nikon body.) But there are, apparently, other ways to achieve the 'same' results. For example using an Achromat as seen in this photo: macro machinery on Flickr - Photo Sharing! (He has some really cool shots, you should check out his stuff anyways.) Please let me know if you have any thoughts on the matter or would like to suggest other possibilities. Of course I'm asking about the difference in quality between the different methods and any other significant factor that would set one apart from the others. Thanks!