The Pentax 645D is an interchangeable medium-format digital SLR camera with a 40-megapixel, 44x33mm Kodak CCD sensor that is approximately 1.7 times larger than a 35mm sensor. Its high-resolution images are rich in gradation and have high dynamic range that can faithfully describe complex textures.
But the 645D is about much more than just resolution: It brings the cost of the medium-format "look" down to a level that more photographers can afford. In his review of the Pentax 645D for the Adorama Learning Center Sandy Ramirez writes: "For the very discerning professional, it's not only about resolution. There is a "look" to Medium Format that cannot be achieved easily with a 35mm full-frame camera, and certainly not with an APS-C camera. This look is due to the fact that the larger sensor (and in the old days film size) requires longer focal lengths and image circles to achieve the same field of view as a 35mm based system. This leads to a shallower depth of field than 35mm-based and APS-based systems."
The 645D is unlike any other Medium Format Digital Single-Lens Reflex (MFDSLR) camera currently in production. While other systems are usually adaptations of old film bodies to digital technology, the 645D is a ground-up digital reinvention of the old 645N II. While it may look like your old film camera, it certainly is not.
The Pentax 645D is definitely a fully digital beast. Bristling with 19 separate controls, almost any parameter can be modified without ever having to get into the menus. While having that many control points sounds daunting, in actual operation the controls are so well laid out, they never really get in the way. Most buttons or knobs only control one parameter, making adjusting the camera to various shooting conditions quite simple, almost second nature.
Another surprise that comes from the complete reinvention is the 645D's AF system. Unlike every other MFDSLR, the Pentax 645D has 11 cross type AF points. While the top of the line Canons and Nikons may have more, for MFDSLRs Pentax is king of the hill in this regard. No other MFDSLR has as advanced an AF system. The selection between the three separate AF modes is handled by one of the dedicated 19 control switches on the 645D.
Overall, the 645D's handling is excelletn, providing all the most important controls directly to the touch. Want to adjust bracketing? There is a dedicated button for that. Want to switch between which memory card you are shooting to? There is a dedicated button for that. Want to quickly switch from shooting RAW to JPEG or vice versa? There is a dedicated button for that as well, and it's even configurable between JPEG, RAW+JPEG and RAW dependent on what your preferred sh ooting style is.
Metering mode? Separate dial switch for that as well as Mirror Lock up, Configurable X-Sync switch, White Balance and White Balance Shift on separate controls and even an additional "Green Button" that can configured to your heart's desire.
The Pentax 645D's high ISO performance is on par with most modern DSLRs, which for the most part puts it ahead of the vast majority of other MFDSLRs that are now on the market. Where this comes in handy is when shooting JPEGs. The JPEG engine on the 645D is quite good, producing very detailed images with little chroma noise at all ISOs up to 1600, with 3200 showing just a tiny bit of noise. Color response is quite good, with the possible exception of the Tungsten setting that tends to be a bit too aggressive creating a slight blue cast. In these situations either shoot a white card or dial in a direct Kelvin reading.
The Pentax 645D represents an amazing value in the Medium Format Digital sector. The Image Quality is on par with similar models from Leica and Phase One, and with it's plethora of available lenses a system that hits the ground running. Its modern controls are a refreshing change from the uneasy truce that most digital backs provide.