IMAGE QUALITY:
The comparison between the Sigma DP2 Quattro and the Pentax 645D is actually total nonsense, because they have completely different audiences. However, you have a few, but for me important similarities. A very similar focal length (when using the Pentax DFA 645 55 / 2.8 with aperture 3.5) and an approximately equal number of megapixels (if you choose the 39 megapixel resolution equivalent). The image quality of both cameras is superb, but the Pentax in my comparisons always a little bit better because it better "works out" the details. The lenses of the two cameras already form at maximum aperture sharply, are when stopping down but getting better. Really good but both cameras only feel with lots of light. In Sigma you should not go higher than ISO 400 (even with B / W is not higher than max. ISO 1600), the Pentax can certainly use the full bandwidth in terms of ISO. This goes only until 1600. When I think of my times with analogue cameras, then it strikes me again and again that I'm never gone higher than 800 ISO. The trend today is unfortunately in direction: in the dead of night to photograph out of his hand. As I take me not out, because who wants to constantly walk around with Tripod, just when the camera, in addition lenses, even quite large fails. As for the Sony A7R, I was very impressed by the image quality at the appearance. But in direct comparison with the Pentax and Sigma DP2 even the Quattro they can not keep up.
OPERATION:
Would during the operation, I can not complain at the Sigma, because it brings a fully configurable Quick menu and the user therefore can adjust almost everything according to his wishes. The Pentax has for quite a lot of buttons, yet in terms of usability but a class of its own. Even if you have the camera on the eye and still want to change the one or other setting, so the camera can remain in the eye. All buttons are useful places and super accessible. Comparing this with the Sony A7 series, then pull the Sony unfortunately the short straw. Sony builds excellent cameras, but the user experience is not given. Ongoing you have one or the other looking knob. This makes permanent not fun.
Size:
As for the size, the Pentax is significantly larger than the compact mirrorless camera conversion of Sony (big plus!), But then the Pentax is not greater than other professional model of the small image segment and noticeably more compact than its competitors in the medium format segment. In addition, the image sensor of the Pentax 645D is significantly larger than the Kleinbildfsensoren (Crop: 0,79x). The size of the Pentax I feel therefore as excellent compromise. Yes, the camera is great! But for what is offered, it is extremely compact.
CONCLUSION:
The Pentax 645D is today (end of 2014) still a top model, which is worth its price and that I can recommend without hesitation.
