Surapon, that's an interesting combination and several years ago I saw Art Wolfe (one of my favorite photographers) using the 1.4x II, 12mm extension tube, and 24-70 f/2.8 (I) to take macro photos of a tree frog in the jungle. I had forgotten about that until this post, but I might have to give that a try now that I have the 12mm tube. It won't replace a true macro, but might be okay if you need a close up shot and don't have a macro lens.
Thanks you, Sir, Dear Friend mackguyver.
Only disadvantage thing for use the tube = We lose 2 stop of exposure(??), And That mean the Photographer must be the Young and Strong Hands Plus Handsome , like you--------Ha, Ha, Ha, Old man like me, I must use the Tripods to shoot at slow shutter speed, If Not will get the Blur Picture, Like when I shoot at the Bigini at the pin point of beautiful Lady on the Beach.
Nice to talk to you again, Have a great Weekend.