Thanks for the reminder to check the cell spacing. I had not thought that the cells could be out of position, but on close examination the rear cell was not fully seated. I think the shutter is original or at least a contemporay of this lens. I have three other shutters almost identical. One has a patent date of 1912. All are 7/8" at the overall outside depth ( before the lenses are screwed in ). I will make the initial resolution test with the rear cell fully seated. Thanks again for the heads up.