Pentax 645D has a 40.0MP Medium format (44 x 33 mm ) sized CCD sensor and features Prime II processor. You can shoot at maximum resolution of 7264 x 5440 pixels with aspect ratios of and 4:3. 645D has a native ISO range of 200 - 1600 which can be boosted to 100 and it can save files in RAW format which gives you a wider room for post processing.
Pentax 645D is not the highest resolution Medium format camera. Fujifilm GFX Eterna 55 with its 102.0MP sensor is leading in this class. Check the comparison of Pentax 645D vs Fujifilm GFX Eterna 55 or take a look at Highest resolution DSLR cameras list.
Pentax 645D DxOMark Sensor Scores
DxOMark is a benchmark that scientifically assesses image quality of camera sensors. Pentax 645D sensor has been tested by DxO Mark and got an overall score of 82 for its image quality. You can find the details of their analysis of Pentax 645D here.
Anti-Aliasing Filter
Another important feature about Pentax 645D's sensor is the lack of anti-alias (Low-pass) filter. Removing anti-aliasing filter increases the sharpness and level of detail but on the other side it also increases the chance of moiré occurring in certain scenes.
Let's look at how the size of the Pentax 645D's Medium format sensor compares with other standard sensor sizes.
Comparison image of Pentax 645D Sensor Size with other standard sensors
Sensor size is what determines the circle of confusion, and therefore how much
depth of field Pentax 645D gives you at any given aperture.
You can
calculate
the exact depth of field for the Pentax 645D
at any focal length, aperture and subject distance, including the hyperfocal distance
for landscapes and the very shallow focus zone you get with long telephoto lenses.
