AZBlue - that's a very obvious question to which I don't have the answer! It would seem entirely logical to roundtrip in DNG. I can't think why I didn't do that. I must try it over the next couple of days. There seemed to be a logical reason for using TIFF over DNG, but I can't for the life of me think what it was!
When words become unclear, I shall focus with photographs. When images become inadequate, I shall be content with silence. - Ansel Adams