Tried out the lens more yesterday. Found that the aperture helps very little. Stopping way down produced severe vignetting, but does not seem to affect Depth of Field much. Focusing is tough because everything looks soft and it's hard to find a focus point. The soft effect tend to be too much. Placing the lens element exposed in the front of the lens probably causes that. As expected, back lit scenes are mostly unusable. Some fine tuning/redesign is in order.
Regardless, it was a fun exercise. My next project is to create my own Lens Baby :-)
All pictures taken with a Canon 5D and my DIY soft focus Lens. Click on the picture to see a larger version.