Ken,
exactly right. Christian Buil had a response curve of the 350D on his website. As expected, an un-modded 350D will cover 4000 - 7000A, and then dies rapidly. He showed that taking out the IR filter makes a big difference but at this time I want to keep the DSLR as is.
I have a Mogg adapter for the DSI + my M42 lenses, haven't tried them yet, but it sounds like a good project for the wekeend....
cheers
Mark