We use the Sigma 8 f3.5 and f4 lens with the Canon 5d and Canon 20d.
On Agnos pole you can set the ring over the stationary part of the lens housing. Set the focus ring to Infinity mark. Then set the camera aperature to F8. F8 is the 'sweet spot' for this lens so that ALL is in focus from 4" in front of the lens glass to infinity.
On a tripod... the ringT must fit over the focus ring. Which means getting the No Parallax point set is important for properly stitching the images.
We did a test with the Sigma 8 lenses... We took 2 photos 1 at f8 and another at f22 (thinking the smaller the hole [read aperature opening the sharper the image]). WRONG. The f22 setting was definately fuzzier in comparision to the f8 image. So set your camera to f8 and let the camera decide the shutter speed.
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EasyPano - Panoweaver