You must have an imported image selected in PHOCUS .
That image must have been shot with a V-SYSTEM lens .
Active the lens correction function and then you can enter your lens parameters .
There is a differentiation between V-SYSTEM and H-SYSTEM shots .
See PHOCUS usersguide page 46 . It does not say much there , as usual in
HASSELBLAD documentation , but it gives you a clou .
When you select a non HASSELBLAD shot image , you can activate the lens corrector but you will not be able to enter lens parameters .