I have a 75/4.5 Caltar II-N in a chrome ringed Copal 0 shutter. I'm trying to replace the shutter with a newer all black Copal 0 shutter. The front element will not screw into the new shutter. There is a shoulder on the lens cell that hits a bezel on the shutter before the threads engage.
Are these shutters not interchangeable? Am I missing something here?