The built-in diopter adjustment on the Phase One XF and the Phase One / Mamiya 645 series camera bodies ranges from -2.5 to +2.5. 

This diopter is suitable for the following cameras:
— Phase One XF Prism Viewfinder, 645DF+, 645DF and 645AF
— Mamiya 645DF+, 645DF and 645AFD I, II & III

There are three additional diopters (available separately) which provide increased dioptric adjustment of ranges from -5 to +2 and which fit in the viewfinder of the Phase One XF and the Phase One / Mamiya 645 series cameras.

Diopter correction lens :        Range of Adjustment
DE401 (standard)                     -2.5 to +2.5  (70277000)
DE402 (nearsighted users)     -5.0 to -2.0   (70278000)
DE403 (farsighted users)          0 to +3.0     (70279000)