Dallmeyer Tripple Achromatic, left, mounted as-is on macro extension tubes and helicoid for Pentax 67. Allows for infinity focus.

Next to it is the same Dallmeyer Triple Achromat with the middle negative achromat removed. Half the back focus, so the lens is mounted in reverse in the helicoid for infinity "soft focus"

At right, a 9" Karl Struss pictorial lens (#282) mounted in macro extension tubes and helicoid. Attains focus at infinity this way.