I used my Nikkor 18-200 zoom lens with a Kenko 36mm extension tube, hand held, taking advantage of image stabilization. When I use this zoom lens with an extension tube, I leave the focus at one setting, and focus on my subject by position. Next, I fine tune the focus using the zoom ring to alter designated focal length—which also changes the point of focus. A little weird, but it works.
[Nikon D300, 18-200mm VR zoom lens at 120mm, 36mm extension tube, 1/15 of a second at f/5.3 and ISO 2,000, hand held using vibration reduction.]