Here's the scene:
Meopta Opemus 5. 39mm mount board.
add Componon-S 80mm – can focus.
add Componon-S 50mm - cannot focus.
I can only get the 50mm to focus when the enlarger head is as near to the base board as possible and the enlargement factor is around 1:1.
At any other height the bellows needs to be wound tightly up to go any where near an image being apparent but completely out of focus.
Mystified by this. Same mount being used in both cases.