This X-844 is needed to mount the Phase One DF or Mamiya AFd-series digital camera to the X2-PRO system. The X2-PRO with this combination excludes the use of the 28 Schneider Digitar, & excludes the use of X-231 & X-232 adapting lensboards for Hasselblad & Mamiya 645-Pro TL optics. The X-844 places the CCD exactly in the optical center of the lens, in horizontal as well as vertical position.