So I finally figured out that C mount lenses don't vignette when using the 2X DTC, and went through my collection again. This includes a variety of flange lengths, some so short I'm afraid to trip the shutter, and some even longer than M4/3. Most will not focus to infinity. I also have about 5 C mount ring extenders, previously used to keep lenses off vidicons. See what I'm getting at? Cheap, sharp, small, fast macro only lenses. I can use some of them after all.