I've acquired this lens yesterday, and perhaps someone can help with the meaning of the indication that is near the f22 aperture engraving: "EXT 324 mm". There is two aperture marks, at max aperture, one is at 4.5 obviously, and the other at 8. I suppose this triplet is not convertible. This lens, as far I could discover, was optimized for portraits and in the lens rear element is written in french to unscrew it 3 turns to make it sharper.

I've made several searches in different forum archives, at the article once published by View camera magazine and in Cooke's website , but nothing specific about this particular lens was found. Any more details about this lens would be appreciated . Thank you all.