Like the Pentax 645D that it replaces, the 645Z has a sensor that measures 43.8x32.8mm (168% the size of a 35mm frame) however Sony has provided the sensor rather than Kodak this time, and the pixel count has been boosted from 40 million to 51 million. As with Hasselblad and Phase One medium format cameras that use this CMOS device, its lack of an anti-aliasing filter boosts detail resolution.

Pentax has also coupled the sensor with a PRIME III image engine, first seen in the Pentax K-3 APS-C format SLR. This enables up to 10 raw images (or 30 images large highest quality JPEGs) to be shot at a maximum speed of approximately three frames per second (fps).

Pentax 645Z
It's a bit of a bulky beast

There are a few other significant upgrades. The maximum sensitivity setting, for example, is now ISO 204,800, significantly higher than the ISO 6400 maximum offered by most other medium format cameras. There's also a tilting 3.2-inch 1,037,000-dot LCD screen which is capable of showing a Live View image and Full HD (1920 x 1080 pixels) movies may be shot at 60i/30P in H.264 format.

In addition to the built-in stereo microphone, the 645Z has a stereo mic port and audio level control is possible.

In addition, Pentax has given the 645Z the SAFOX 11 phase-detection autofocus (AF) system found in the K-3. This has 27 AF points, 25 of which are the more sensitive cross-type. It's also capable of working down to -3EV.

Pentax 645Z
Luckily, the camera is weather sealed if you're caught in the rain

Exposure can be controlled manually or automatically with information being provided by the Pentax Real-Time Scene Analysis System. This consists of an 86,000-pixel RGB light-metering sensor and an algorithm. Pentax claims this improves on exposure-control accuracy and it provides data to enhance autofocusing accuracy and white-balance adjustment.

There are also two SD/SDHC/SDXC cards ports with the second port compatible with Flu cards to allow wireless shutter release and image transfer and via a smartphone.

Build and handling

Pentax has used the same design and control layout for the 645Z as it did for the 645D, so those upgrading will find the transition pretty smooth. The body is covered fairly liberally with controls that give a quick route to key features such as sensitivity, white balance and exposure compensation.

Like the 645D, the 645Z has seals that make it weather and dust resistant. It also has the same deep grip and, despite its larger size and relatively heavy weight (over 1.5Kg without a lens), it feels comfortable in the hand. It really is feasible to use this camera hand-held and thanks to its impressive sensitivity range it is possibly that this camera will be used so more than any other digital medium format camera.

Pentax 645Z
The grip is deep and easy to hold on to

I used a pre-production sample of the camera with the weather resistant 21mm lens mounted for about 30 minutes in persistent drizzle and didn't encounter any problems. Despite the water on the grip and covering the buttons and dials it continued to function correctly, and I was able to keep a good grip on it.

As the user interface is very similar to that of Pentax's K-series cameras it's very easy to get to grips with the 645Z, and even those who have never used a medium format camera before will soon feel comfortable using it.

Being an SLR, the 645Z has a reflex mirror that lifts to allow an exposure to be made. Naturally this is quite a large unit and, while it's not quite the door-slam of some medium format models, you are certainly aware of its movements.

Pentax 645Z
Cleverly, the screen info flips when you turn it to portrait orientation

The viewfinder is large and bright, but with 98% coverage it doesn't quite display whole image and you can expect to find the odd extra inclusion around the edges of the frame on occasion. The LCD screen is also clear and provides a detailed view, whether composing using Live View mode or reviewing images. The fact that the screen tilts is especially useful when composing images on a tripod in the studio or when out shooting landscapes.

It's also helpful that the screen's display can be set to rotate to make it easier to read when shooting in upright format.

Performance

I have only used a pre-production sample of the 645Z to date, but it is sufficiently far forward in its development for me to be able to publish a few images here at reduced size. We are told that the hardware is final, but the firmware is not, and these images should not be taken to represent final image quality.

The key advantage of having 51 million effective pixels on a medium format sensor is that it's possible to record lots of detail. Also, because those pixels are relatively large, they generate a strong signal that means noise levels can be kept down. This is immediately apparent in the images from the pre-production sample of the 645Z – they have a huge amount of sharp detail and little noise at the low to mid-range sensitivity settings.

Even at the highest sensitivity setting (ISO 204,800) noise is controlled comparatively well. There is some coloured speckling visible, but detail appears to be better retained than in images from small format SLRs with such settings. Nevertheless, most photographers will still only want to use it for emergencies.

Stepping down to ISO 6400 results in images that look significantly better, with plenty of detail, making using this setting realistic.

The raw files, which are in the convenient DNG format, naturally have more detail than simultaneously captured JPEGs, and it's possible to strike a nice balance between detail visibility and noise suppression during post-capture processing.

Pentax 645Z
The tilting screen is great for low tripod shots

Thanks to the 645Z's relative portability the auto white balance and general purpose metering systems are more likely to be used than with some more studio-bound medium format cameras. Our initial tests indicate that these perform well, with the auto white balance system delivering natural looking images that reflect the shooting conditions. The metering system also behaves well, reacting as you might expect to bright subjects and requiring a little exposure compensation to produce a correctly exposed image.

While the 645Z's AF system can't compete with a high-end small format SLR's, it is pretty impressive considering the size and weight of the elements inside the compatible lenses. It's much faster than most SLRs' Live View AF systems, and even in quite low light it homed in on its target decisively with no hunting. It's a viable option for hand-held photography.

Verdict

It may be at the more affordable end (affordable being a relative term) of the digital medium format camera market, but the Pentax 645Z gives a very good account of itself.

For a start, the average enthusiast photographer who knows his or her way around a mid-to-high-end SLR will find that they quickly get to grips with its control layout and menu arrangement. In addition the pre-production sample images indicate that users will be rewarded with high quality photographs provided that they are prepared to take some control over exposure in what are traditionally considered challenging conditions for a light meter.

The tilting screen and Live View capability add an extra level of convenience to medium format shooting, and I'm looking forward to testing a full-production sample in the near future.