Thanks for the responses guys!

@ HD - That video was very helpful with getting me to understand those charts. Thanks much for providing the link!

@ Sean & Ben - I do have the Kenko extension tube set. I am ok with using the 12mm but when it comes to using the 20mm & 36mm, I have somewhat more difficulty focusing. With those or with stacking, it takes me forever to get focus unless I am setup well with my tripod and a macro slider. I sold my slider a long while back but maybe I should look at getting another and just using the tubes more often. More practice may make them become easier to use for me.

BTW Ben - AWESOME shots!! I still have my 70-200mm f4 IS but never used tubes on it ...you may have inspired me to give it a shot!

Question: The guy that may sell me his 105mm just emailed a couple photos he took with the lens. Is it "proper" for me to post them here?? I have a question on something I am seeing in the photos. I do not know if it is something caused by the camera, the lens, or in post.