When I started thinking about taking macro/close up work more seriously, everything I read pointed me in the direction of a macro lens. Unfortunately I missed Ken Rockwell's article that pointed out that moderate length macro lenses are not great for some insects because you have to get too close. So, while I like the 60mm macro, it wasn't really getting me what I wanted - dragonflies. Conventional wisdom is that ext tubes are not as useful at longer focal lengths because they don't make "that much" difference in magnification. Then Scott said, "get some tubes". So I did. What exactly do Kenko's Ext tubes get you on the 100-300? I'm glad you asked. Code: Focal Length Ext Tube Minimum Focus Distance Horiz FOV 300 No 58" 80mm 300 Yes 46" 50mm 200 No 57" 120mm 200 Yes 37" 55mm 100 No 55" 215mm 100 Yes 20" 48mm The other change that Ext tubes bring is the loss of focus at infinity. A quick test shows that the far focus distance with tubes is 27" (68mm Fov) at 100mm and 76" (123mm Fov) at 200mm. I couldn't measure 300mm because the room was too small. Now I'm off to the local lake to look for bugs.