Sony A99 II has a
42.0MP Full frame (35.9 x 24 mm ) sized BSI-CMOS sensor and features Bionz X processor. On the other hand, Pentax 645D has a
40.0MP Medium format (44 x 33 mm ) sized CCD sensor and features Prime II processor.
Another similarity between these two cameras is that both Pentax 645D and Sony A99 II sensors lack anti-alias (Low-Pass) filters. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moiré occurring in certain scenes.
Below you can see the A99 II and 645D sensor size comparison.
Sensor Size and Resolution Comparison image of Sony A99 II and Pentax 645D Cameras
As seen above, Pentax 645D has a 1.7x Larger sensor area than Sony A99 II. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.
DxOMark Sensor Scores
Both Sony A99 II and Pentax 645D sensors have been tested by DxoMark. DxoMark scores camera sensors for color depth (DXO Portrait), dynamic range (DXO Landscape) and low-light sensitivity (DXO Sports), and also gives them an overall score. Of the two cameras that we are comparing, A99 II has scored 92, 10 points higher than 645D.
Model
Overall
Color Depth
Dynamic Range
Low-light ISO
Sony A99 II
92
25.4 bits
13.4 Evs
2317 ISO
Pentax 645D
82
24.6 bits
12.6 Evs
1262 ISO
Sensor size sets the circle of confusion, so it drives how much depth of field each
of these bodies gives you at a given aperture. You can calculate it exactly for the
Sony A99 II
or the
Pentax 645D ,
including hyperfocal distance.
One thing to watch when comparing these two: they have different sensor sizes
(Full frame versus Medium format),
so compare them at the same framing rather than the same focal length.
Put the same focal length on the smaller sensor and it will show less depth of
field, not more, because it also crops tighter. The calculator shows the
full frame equivalent focal length for each body so you can match the framing.
