There may be differences in the way the focus ring bumps against the infinity stop. Older prontors have the infinity stop on the outside. Later versions have the stop underneath the focus ring. You might end up with an apotar lens with a faceplate that says agnar.
A Zeiss Ikonta that I have needs some shutter system attention. However I have unscrewed the front focusing lens after removing the focusing stop screw. However There is a second bushing with an internal focusing thread that has to be removed before the speed cam plate can be removed so tha t attention can be given to the to the shutter mechanism. Does this bushing simply unscrew?
