This will be old hat for you, but I can still get carried away by the mechanical wonder of the original curtain shutter and the incremental improvement it underwent. Please be lenient towards a relative newcomer to LTM innards
iPhone slow motion of IIIa timing mechanism:
http://www.galerie-elsner.de/video/IIIa.MOV
[ The video file is 8 MB, so those on a mobile or on a slow internet connection might refrain from clicking the link ]
This is from the original German patent published in 1926 (declared valid as of 1924):