The 51.4-million-pixel 645Z DSLR – an improvement on the 40-million-pixel sensor on the 645D – incorporates a Safox 11 AF module with 27 AF points (including 25 cross-type sensors).
Other features include a Prime III image-processing engine, a top ISO of 204,800 and three frames per second shooting (compared to 1.1fps on the 645D).
The larger 3.2in, tilting LCD screen carries a resolution of 1.037 million dots.
Boasting 76 seals, the 645Z is claimed to be weather-resistant and dustproof.
The exterior housing and LCD monitor frame are made of magnesium alloy, while the chassis is built from die-cast aluminium.
Also on board is full HD video. Similar to the interval video mode on the Pentax K3, the 645Z shoots time-lapse video at 4K resolution (3840×2160 pixels).
On-board Wi-Fi means images can be shared via a smartphone, for example.
Due out at the end of May, the 645Z will cost Â£6,799.99 body only, or Â£7,699.99 with a 55mm lens.
The original Pentax 645D was launched in 2010.
Pentax unveils 645Z DSLR; confirms UK price