I did a little more with my setup and the 58mm has 70mm; from the front element to the subject as working distance. That's at 100mm extension. The 150mm lens has 390mm of working distance at 150mm extension and the 105 has 200mm of working distance at 150mm extension.
here is a shot of the rails to give you an idea of how they attach to the QR plate on the tripod.
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So you can move the whole unit front and back as well as side to side.
here's a sample image from the 105mm at 150mm extension using a Vivitar 6000 ringlight on the K10D, shot in Manual.
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