I have a tamron 17-50 f/2.8 DC with a minimum focal distance of 10 inches and a Sigma 70-300 APO 1:2 Macro with a minimum of 150/95 cm (normal/macro) that I use on a Rebel XT. The minimums for the Sigma are way too large for me and it would also be nice to reduce the tamron's minimum too. Unfortunately I don't know much about extension tubes excepting that they reduce the minimum focal distance. I am planning on getting the Kenko 12, 20 and 36mm tube set from BH at this link. Are this compatible with my lenses and will they reduce the minimum focus distance significantly?
