The smc Pentax-DA 645 lenses can be used exclusively with Pentax 645-series medium-format digital SLR cameras. Their image circle is specialized for image sensors in Pentax 645-series medium-format digital SLR cameras and their optical systems are optimized for the characteristics of digital images. The DA 645 lenses are not compatible with 645-series film SLR cameras.
The DA 645 lenses do not have an aperture ring. Aperture settings are controlled automatically as if set to the auto "A" position.
When autofocusing is finished, it is possible to make fine adjustments by hand using the "Quick-Shift Focus System".