Summary: The 645D will no doubt attract a niche audience, though its almost-£10k price tag is firmly out of reach for the majority. The experience of using a medium format digital camera is very different from a DSLR and has many advantages, especially for landscape photographers. To be clear: the 645D is less of a studio camera than its competition, but its weather-sealed single body design firmly fixes it as one to use in the field or where large, resolute files are a must.
Summary: Each of these two cameras are excellent at what they do best. For example, the 1Ds Mark III is a more flexible tool, capable of holding its own when high levels of detail are needed, but without sacrificing aspects for handling such as the compact 35mm form factor, impressive autofocus and high speed continuous shooting.
Pros: Superb sharpness and resolution, Excellent dynamic range, Good handling, Weather Sealing, Good white balance performance, Lowest price medium format digital currently available, Compatible with Pentax 645 lenses, Excellent build quality, Superb autofocus, High speed continuous shooting, Decent sharpness and resolution, Vibrant contrasty images, Good colours straight from the camera, 1/250sec flash sync speed
Cons: Meter often underexposes, Slow continuous autofocus, 1/125 flash sync speed, Softening at higher ISOs, Poor white balance performance, Viewfinder a little difficult to use when wearing glasses