Pentax Focusing Screen UB-21 - Matte field and split-image spot
Note:
These screens DO NOT fit the newer 645n. Different screens required
Pentax offers four additional interchangeable screens for the 645 camera
UA-21 - Matte field and microprism spot
UE-20 - Matte field only
UG-20 - Matte field and cross hairs
UC-21 - Matte field and and split-image spot with microsprism collar