Pentax 645Z Review
Autofocus and Focusing Aides
When it comes to focusing, the Pentax 645Z is a considerable improvement over the 645D and a very powerful camera in its own right. Its biggest advantage by far is the mere presence of live view, which makes it a breeze to magnify an image and fine-tune the focus to perfection, something that was not possible with the 645D. The 645Z's live view mode also features focus peaking as well as a high-performance contrast detect algorithm, thus giving you plenty of focusing options for a variety of scenarios.
Let's not forget that live view gives you 100% frame coverage, which the viewfinder doesn't. Thus, with the 645Z, you're also able to fine-tune your composition more precisely.
On top of this, the 645Z's viewfinder autofocus system has also seen improvements. This makes for a win-win-win in the focusing department.
Viewfinder Autofocus
The Pentax 645Z features a 27-point phase detection autofocus system known as SAFOX XI, which it inherits from the Pentax K-3. 25 of these AF points are cross-type, while 3 points in the center column are able to obtain even higher accuracy when paired with F2.8 lenses.
Of these AF points, you can choose to use 1, 9, 25, or 27 in either AF-S (single) or AF-C (continuous) mode. These are subdivided into center-point, select, and auto area modes. The menu further provides both a focus priority and a release priority setting, and an AF expansion options aids in tracking (see our Pentax K-3 review for details).
Regardless, the key feature of this AF system is its ability to focus in as little as -3EV of light. Whether you're shooting in a dim studio or a moonlit landscape, expect the 645Z to be able to focus reliably and precisely. Do note that the AF speed is reduced considerably in such scenarios, however.
The -3EV figure isn't just a number on a piece of paper; the AF really works in virtually no light! This is especially important for the 645Z, since it lacks an AF assist beam.
645Z viewfinder (to scale)
There is only one major issue with the 645Z's viewfinder autofocus system, and it should be apparent from the illustration above. Since SAFOX IX is designed for APS-C cameras (where it already only covers about half of the viewfinder), it covers a very small portion of the 645Z's medium-format viewfinder. Thus, we like to think of the 645Z's many AF points as a single, highly-precise AF point. You can safely keep the camera in auto 27-point mode without thinking twice.
If you want to be able to focus on a different part of your subject, the focus-recompose method will therefore often be necessary, which can be inconvenient when on a tripod. You can also use live view AF, which offers considerably greater frame coverage (see below).
We find the 645Z's viewfinder AF speed to be satisfactory. Pentax's medium format lenses aren't the fastest to focus due to their size, but at least DA/D FA lenses have silent AF motors.
For those planning to use screwdrive (FA series) lenses, note that the 645Z incorporates a more powerful screwdrive motor than the 645D, so screwdrive AF performance has been improved (on top of the 645Z's ability to measure focus more quickly and precisely).
We did not test the 645Z's viewfinder autofocus in AF-C (continuous) mode. However, since the AF hardware is that same as that of the Pentax K-3, which was limited more by lens AF speed than SAFOX XI performance, we would expect the same to apply to the 645Z. This camera isn't going to outshine a D4s or 1Dx for shooting high-speed sports. The interface that lets you switch AF points and modes could also use improvement. More details can be found in our Pentax K-3 review.
Live View Autofocus
The 645Z offers a variety of focusing modes in live view. These modes are accessible when shooting stills, and also prior to starting video recording:
- Face detection AF
- Tracking
- Auto-area AF
- Select AF
- Spot AF
While videos are being recorded, only rudimentary on-demand autofocus is available.
645Z AF modes
Let's start with auto area AF. In this mode, the camera does its best of determining and focusing on the subject within a generously-sized grid of 15 AF points. After focusing, the camera will display which of the AF points (1 or more) are in focus. A similar AF system is used in the Pentax Q7, K-3, K-50, and K-500.
Auto area AF in video live view
Face detection AF is very similar, except that it will look for and focus on faces when applicable. When no faces are detected, the AF behavior is identical to auto area AF.
Let's leave Tracking alone, as it continues to be a rudimentary implementation (phase detection in live view would be necessary for reliable tracking).
In select AF mode, you tell the camera how big or small the AF area should be. The camera then focuses just like in auto area AF mode, but in a different area. You can also move the AF area around in this mode, and among the selectable options is a 1x1 rectangle representing a single AF area.
AF locked on a single point in select mode
To change the AF area, simple press the AF area button on the back of the camera while in live view. You will then be able to cycle through the 4 options below and position the AF area as desired.
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Last (and least, in our opinion) is spot AF mode. In this mode, the camera is limited to focusing on a small area in the center of the frame. Unlike in select mode, you cannot move the AF area around, even though it has the same size. Thus, this mode is only recommended when you want to use the select mode to store a different size preset.
Live View AF Performance
Generally speaking, the best live view AF speed can be obtained in auto area AF or select mode, since more data allows the camera to perform a more accurate evaluation of the scene. In spot AF or when you select a 1x1 AF area, AF accuracy can be spotty depending on the nature of your subject.
Pentax's live view AF implementation is actually remarkably good for still subjects and varied scenes. It is speedy, accurate, and is only fooled in very low light or when there is little contrast. We found the 645Z's contrast detect autofocus to be superior to that of Nikon cameras such as the D800 or D810.
As with viewfinder AF, the live view AF slows down as the amount of ambient light decreases.
Since medium format lenses are physically larger and generally have longer focusing throws than K-mount lenses, you won't get the lightning-fast live view AF performance of the K-3 or K-S1, but now we're just being picky.
AF Demonstration
Below is a demonstration of typical AF speed and how AF speed changes in slow light. Note that the camera never mis-focused.
Manual Focusing
The 645Z's manual focusing aids are excellent. In addition to using viewfinder AF confirmation, you can utilize live view to magnify the scene with or without focus peaking. The fact that the rear LCD screen can tilt makes it easy to verify the focus when shooting indoors or outdoors on a tripod. We made extensive use of this feature while photographing landscapes.
| Peaking Off | Peaking On | |
| Zoomed out |  |  |
| Zoomed in |  |  |
Focus peaking adds white outlines to things that are in focus, thus making it easier for the photographer to manually adjust the focus. As you can see above, peaking is very helpful in determining that the yellow locomotive is in fact in focus. The white outlines can be a bit overwhelming and/or distracting when zoomed out, however. There are unfortunately no customization options for focus peaking apart from the on/off option.
Focus peaking is available for stills and starting video recording. It is not available during recording.
The only other complaint we have is that as soon as you activate live view autofocus (i.e. by pressing the AF button or half-pressing the shutter button), the camera immediately exits out of live view magnification and instead shows the whole scene. This is very annoying when one intends to start with the AF system's suggestion and then fine-tune manually, since you will need to zoom back in every time you focus or recompose.
HDMI Output
When you connect the 645Z to a screen or TV using an HDMI cord, you'll be able to view the live view output or the currently-selected image in playback mode. The maximum HDMI resolution is full HD (1080i).
AF Verdict
All in all, the focusing capabilities of the 645Z will exceed the expectations of studio and landscape photographers. The presence of live view, the tilting LCD screen, and the latest in Pentax AF technology all work in harmony to deliver flexibility and performance wherever your assignments take you.
