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Pentax 645Z versus Sony A7R III

The Pentax 645Z and the Sony Alpha A7R III are two digital cameras that were officially introduced, respectively, in April 2014 and October 2017. The 645Z is a DSLR, while the A7R III is a mirrorless interchangeable lens camera. The cameras are based on a medium format (645Z) and a full frame (A7R III) sensor. The Pentax has a resolution of 51.1 megapixel, whereas the Sony provides 42.2 MP. Read on to find out how these two cameras compare with respect to their size, their sensors, their features, and their reception by expert reviewers.

Body comparison: Pentax 645Z vs Sony A7R III

The side-by-side display below illustrates the physical size and weight of the Pentax 645Z and the Sony A7R III. The two cameras are presented according to their relative size. Three consecutive views from the front, the top, and the rear side are shown. All width, height and depth measures are rounded to the nearest millimeter. You can also use the toggle button to switch to a percentage comparison if you prefer that the measures are being expressed in relative terms (in this case, the camera on the left side – the 645Z – represents the basis for the calculations across all the size and weight measures).

Compare Pentax 645Z vs Sony A7R III
Compare 645Z versus A7R III top
Compare 645Z and A7R III rear

If the front view area (width x height) of the cameras is taken as an aggregate measure of their size, the Sony A7R III is considerably smaller (33 percent) than the Pentax 645Z. Moreover, the A7R III is substantially lighter (58 percent) than the 645Z. In this context, it is worth noting that both cameras are splash and dust-proof and can, hence, be used in inclement weather conditions or harsh environments.

The above size and weight comparisons are to some extent incomplete since they do not consider the interchangeable lenses that both of these cameras require. Hence, you might want to study the specifications of available lenses in order to get the full picture of the size and weight of the two camera systems.

The adjacent table lists the principal physical characteristics of the two cameras alongside a wider set of alternatives. If you want to switch the focus of the display and review another camera pair, just select a new right or left comparator from among the camera models in the table. Alternatively, you can also move across to the CAM-parator tool and choose from the broad selection of possible camera comparisons there.

Camera Body Specifications
  Camera
Model
Camera
Width
Camera
Height
Camera
Depth
Camera
Weight
Battery
Life
(CIPA)
Weather
Sealing
(yes/no)
Camera
Launch
(announced)
Launch
Price
(USD)
Street
Price
(USD)
Used
Price
(USD)
Camera
Model
Pentax 645Z» 156 mm 117 mm 123 mm 1550 g 650 Y Apr 2014 8,499 i i Pentax 645Z
Sony A7R III« 127 mm 96 mm 74 mm 650 g 650 Y Oct 2017 3,199 i i Sony A7R III
Canon 5DS R« » 152 mm 116 mm 76 mm 930 g 700 Y Feb 2015 3,699 i i Canon 5DS R
Canon 5DS« » 152 mm 116 mm 76 mm 930 g 700 Y Feb 2015 3,699 i i Canon 5DS
Hasselblad X1D« » 150 mm 98 mm 71 mm 725 g .. Y Jun 2016 8,995 i i Hasselblad X1D
Leica SL« » 147 mm 104 mm 39 mm 847 g 400 Y Oct 2015 7,450 i i Leica SL
Nikon D750« » 141 mm 113 mm 78 mm 750 g 1230 Y Sep 2014 2,299 i i Nikon D750
Nikon D810« » 146 mm 123 mm 82 mm 980 g 1200 Y Jun 2014 3,299- i Nikon D810
Nikon D4S« » 160 mm 157 mm 91 mm 1350 g 3020 Y Feb 2014 6,499- i Nikon D4S
Nikon D7100« » 136 mm 107 mm 76 mm 765 g 950 Y Feb 2013 1,199- i Nikon D7100
Nikon D610« » 141 mm 113 mm 82 mm 850 g 900 Y Oct 2013 1,999 i i Nikon D610
Pentax 645D« » 156 mm 117 mm 119 mm 1480 g 800 Y Mar 2010 9,995- i Pentax 645D
Sony A7 III« » 127 mm 96 mm 74 mm 650 g 610 Y Feb 2018 1,999 i i Sony A7 III
Sony A99 II« » 143 mm 104 mm 76 mm 849 g 490 Y Sep 2016 3,199 i i Sony A99 II
Sony A7R II« » 127 mm 96 mm 60 mm 625 g 290 Y Jun 2015 3,199- i Sony A7R II
Sony A7 II« » 127 mm 96 mm 60 mm 599 g 350 Y Nov 2014 1,999- i Sony A7 II
Sony A7R« » 127 mm 94 mm 48 mm 465 g 340 Y Oct 2013 2,299- i Sony A7R

Any camera purchase will naturally be influenced heavily by the price. The listed launch prices provide an indication of the market segment that the manufacturer of the cameras have been targeting. The A7R III was launched at a markedly lower price (by 62 percent) than the 645Z, which puts it into a different market segment. Usually, retail prices stay at first close to the launch price, but after several months, discounts become available. Later in the product cycle and, in particular, when the replacement model is about to appear, further discounting and stock clearance sales often push the camera price considerably down.

 

Sensor comparison: Pentax 645Z vs Sony A7R III

The size of the sensor inside a digital camera is one of the key determinants of image quality. A large sensor will generally have larger individual pixels that offer better low-light sensitivity, provide wider dynamic range, and have richer color-depth than smaller pixels in a sensor of the same technological generation. Furthermore, a large sensor camera will give the photographer more possibilities to use shallow depth-of-field in order to isolate a subject from the background. On the downside, larger sensors tend to be more expensive and lead to bigger and heavier cameras and lenses.

Of the two cameras under consideration, the Pentax 645Z features a medium format sensor and the Sony A7R III a full frame sensor. The sensor area in the A7R III is 40 percent smaller. As a result of these sensor size differences, the cameras have a format factor of, respectively, 0.79 and 1.0. The sensor in the 645Z has a native 4:3 aspect ratio, while the one in the A7R III offers a 3:2 aspect.

Pentax 645Z and Sony A7R III sensor measures

With 51.1MP, the 645Z offers a higher resolution than the A7R III (42.2MP), but the 645Z nevertheless has larger individual pixels (pixel pitch of 5.30μm versus 4.52μm for the A7R III) due to its larger sensor. However, the A7R III is a somewhat more recent model (by 3 years and 6 months) than the 645Z, and its sensor might have benefitted from technological advances during this time that further enhance the light gathering capacity of its pixels. Coming back to sensor resolution, it should be mentioned that neither of the two cameras has an anti-alias filter installed, so they are able to capture all the detail the sensor resolves.

Unlike the 645Z, the A7R III has the capacity to capture high quality composite images by combining multiple shots after shifting its sensor by miniscule distances. This multi-shot, pixel-shift mode is most suitable for photography of stationary objects (landscapes, studio scenes).

645Z versus A7R III MP

Consistent information on actual sensor performance is available from DXO Mark for many cameras. This service is based on lab testing and assigns an overall score to each camera sensor, as well as ratings for dynamic range ("DXO Landscape"), color depth ("DXO Portrait"), and low-light sensitivity ("DXO Sports"). The Overall DXO ratings for the two cameras under consideration are close, suggesting that they provide similar image quality. The following table provides an overview of the physical sensor characteristics, as well as the sensor quality measurements for a selection of comparators.

Sensor Characteristics
  Camera
Model
Sensor
Class
Resolution
(MP)
Horiz.
Pixels
Vert.
Pixels
Video
Format
DXO
Portrait
DXO
Landscape
DXO
Sports
DXO
Overall
Camera
Model
Pentax 645Z» Medium Format 51.1 8256 61921080/60i26.014.74505101Pentax 645Z
Sony A7R III« Full Frame 42.2 7952 53044K/30p26.014.73523100Sony A7R III
Canon 5DS R« » Full Frame 50.3 8688 57921080/60p24.612.4230886Canon 5DS R
Canon 5DS« » Full Frame 50.3 8688 57921080/60p24.712.4238187Canon 5DS
Hasselblad X1D« » Medium Format 51.3 8272 62001080/25p26.214.84489102Hasselblad X1D
Leica SL« » Full Frame 24.0 6000 40004K/30p25.013.4182188Leica SL
Nikon D750« » Full Frame 24.2 6016 40161080/60p24.814.5295693Nikon D750
Nikon D810« » Full Frame 36.2 7360 49121080/60p25.714.8285397Nikon D810
Nikon D4S« » Full Frame 16.2 4928 32801080/60p24.413.3307489Nikon D4S
Nikon D7100« » APS-C 24.0 6000 40001080/60p24.213.7125683Nikon D7100
Nikon D610« » Full Frame 24.2 6016 40161080/30p25.114.4292594Nikon D610
Pentax 645D« » Medium Format 39.5 7264 5440-24.612.6126282Pentax 645D
Sony A7 III« » Full Frame 24.0 6000 40004K/30p25.014.7373096Sony A7 III
Sony A99 II« » Full Frame 42.2 7952 53044K/30p25.413.4231792Sony A99 II
Sony A7R II« » Full Frame 42.2 7952 53044K/30p26.013.9343498Sony A7R II
Sony A7 II« » Full Frame 24.0 6000 40001080/60p24.913.6244990Sony A7 II
Sony A7R« » Full Frame 36.2 7360 49121080/60p25.614.1274695Sony A7R

Many modern cameras are not only capable of taking still images, but can also record movies. Both cameras under consideration are equipped with sensors that have a sufficiently high read-out speed for moving images, but the A7R III provides a better video resolution than the 645Z. It can shoot movie footage at 4K/30p, while the Pentax is limited to 1080/60i.

 

Feature comparison: Pentax 645Z vs Sony A7R III

Apart from body and sensor, cameras can and do differ across a range of features. For example, the A7R III has an electronic viewfinder (3686k dots), while the 645Z has an optical one. Both systems have their advantages, with the electronic viewfinder making it possible to project supplementary shooting information into the framing view, whereas the optical viewfinder offers lag-free viewing and a very clear framing image. The table below summarizes some of the other core capabilities of the Pentax 645Z and Sony A7R III in connection with corresponding information for a sample of similar cameras. If needed, the dpreview camera hub, for example, contains further detail on the cameras' specs.

Core Features
  Camera
Model
Viewfinder
(Type or
'000 dots)
Control
Panel
(yes/no)
LCD
Size
(inch)
LCD
Resolution
('000 dots)
LCD
Attach-
ment
Touch
Screen
(yes/no)
Shutter
speed
(1/sec)
Shutter
flaps
(1/sec))
Build-in
Flash
(yes/no)
Build-in
Image
Stab
Camera
Model
Pentax 645Z»optical Y 3.2 1037 tilting n 4000 3.0 n n Pentax 645Z
Sony A7R III«3686 n 3.0 1440 tilting Y 8000 10.0 n Y Sony A7R III
Canon 5DS R« »optical Y 3.2 1040 fixed n 8000 5.0 n n Canon 5DS R
Canon 5DS« »optical Y 3.2 1040 fixed n 8000 5.0 n n Canon 5DS
Hasselblad X1D« »2360 n 3.0 920 fixed Y 2000 2.3 n n Hasselblad X1D
Leica SL« »4400 Y 3.0 1040 fixed Y 8000 11.0 n n Leica SL
Nikon D750« »optical Y 3.2 1229 tilting n 4000 6.0 Y n Nikon D750
Nikon D810« »optical Y 3.2 1229 fixed n 4000 5.0 Y n Nikon D810
Nikon D4S« »optical Y 3.2 921 fixed n 8000 11.0 n n Nikon D4S
Nikon D7100« »optical Y 3.2 1229 fixed n 8000 6.0 Y n Nikon D7100
Nikon D610« »optical Y 3.2 921 fixed n 4000 6.0 Y n Nikon D610
Pentax 645D« »optical Y 3.0 921 fixed n 4000 1.1 n n Pentax 645D
Sony A7 III« »2359 n 3.0 922 tilting Y 8000 10.0 n Y Sony A7 III
Sony A99 II« »2400 Y 3.0 1229 full-flex n 8000 12.0 n Y Sony A99 II
Sony A7R II« »2400 n 3.0 1229 tilting n 8000 5.0 n Y Sony A7R II
Sony A7 II« »2400 n 3.0 1230 tilting n 8000 5.0 n Y Sony A7 II
Sony A7R« »2400 n 3.0 1230 tilting n 8000 4.0 n n Sony A7R

Both the 645Z and the A7R III are current models that good online retailers will have in stock. You can check the latest prices, for example, at amazon. The 645Z replaced the earlier Pentax 645D, while the A7R III followed on from the Sony A7R II.

Review summary: Pentax 645Z vs Sony A7R III

So what conclusions can be drawn? Is the Pentax 645Z better than the Sony A7R III or vice versa? Below is a summary of the relative strengths of each of the two contestants.

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Reasons to prefer the Pentax 645Z:

  • More detail: Offers more megapixels (51.1 vs 42.2MP) with a 8% higher linear resolution.
  • Better low-light sensitivity: Requires less light for good images (0.4 stops ISO advantage).
  • Brighter framing: Features an optical viewfinder for clear, lag-free composition.
  • Easier setting verification: Has an LCD display on top to control shooting parameters.
  • Larger screen: Has a bigger rear LCD (3.2" vs 3.0") for image review and settings control.
  • More heavily discounted: Has been available for much longer (launched in April 2014).

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Advantages of the Sony Alpha A7R III:

  • High quality composites: Can combine several shots after pixel-shifting its sensor.
  • Better video: Provides higher definition movie capture (4K/30p vs 1080/60i).
  • More framing info: Has an electronic viewfinder that displays shooting data.
  • More detailed LCD: Has a higher resolution rear screen (1440k vs 1037k dots).
  • Fewer buttons to press: Has a touchscreen to facilitate handling and shooting adjustments.
  • Faster shutter: Has higher mechanical shutter speed (8000/sec vs 4000/sec) to freeze action.
  • Faster burst: Shoots at higher frequency (10 vs 3 flaps/sec) to capture the decisive moment.
  • More compact: Is smaller (127x96mm vs 156x117mm) and will fit more readily into a bag.
  • Less heavy: Has a lower weight (by 900g or 58 percent) and is thus easier to take along.
  • More legacy lens friendly: Can use many non-native lenses via adapters.
  • Sharper images: Has stabilization technology build-in to reduce the impact of hand-shake.
  • More affordable: Was introduced into a lower priced category (62 percent cheaper at launch).
  • More modern: Reflects 3 years and 6 months of technical progress since the 645Z launch.

If the count of individual advantages (bullet points above) is taken as a guide, the A7R III is the clear winner of the contest (13 : 6 points). However, the pertinence of the various camera strengths will differ across photographers, so that you might want to weigh individual camera traits according to their importance for your own imaging needs before making a camera decision.

645Z 06:13 A7R III

In any case, while the comparison of technical specifications can provide a useful overview of the capabilities of different cameras, it says nothing about, for example, the handling, responsiveness, and overall imaging quality of the 645Z and the A7R III in practical situations. User reviews that are available, for instance, at amazon can sometimes shed light on these issues, but such feedback is all too often partial, inconsistent, and inaccurate. This is why expert reviews are important. The adjacent table relays the overall verdicts of several of the most popular camera review sites (cameralabs, dpreview, ephotozine, imaging-resource, photographyblog). You can find the full text of the reviews by clicking on the site logo in the table header.

Review Scores
  Camera
Model
cameralabs dpreview ephotozine imaging-resource photographyblog Camera
Launch
(announced)
Launch
Price
(USD)
Street
Price
(USD)
Used
Price
(USD)
Camera
Model
Pentax 645Z»--4.5/55/55/5 Apr 2014 8,499 i i Pentax 645Z
Sony A7R III«HiRec90/1004.5/55/55/5 Oct 2017 3,199 i i Sony A7R III
Canon 5DS R« »Rec83/1005/55/54.5/5 Feb 2015 3,699 i i Canon 5DS R
Canon 5DS« »Rec83/1004.5/55/54.5/5 Feb 2015 3,699 i i Canon 5DS
Hasselblad X1D« »rev81/100--4/5 Jun 2016 8,995 i i Hasselblad X1D
Leica SL« »-84/1004.5/54/54/5 Oct 2015 7,450 i i Leica SL
Nikon D750« »HiRec90/1004.5/55/54.5/5 Sep 2014 2,299 i i Nikon D750
Nikon D810« »-86/1005/54.5/54.5/5 Jun 2014 3,299- i Nikon D810
Nikon D4S« »--4.5/55/54.5/5 Feb 2014 6,499- i Nikon D4S
Nikon D7100« »HiRec85/1004.5/55/54.5/5 Feb 2013 1,199- i Nikon D7100
Nikon D610« »HiRec87/1004.5/54.5/54.5/5 Oct 2013 1,999 i i Nikon D610
Pentax 645D« »---4.5/5- Mar 2010 9,995- i Pentax 645D
Sony A7 III« »HiRec89/1005/55/55/5 Feb 2018 1,999 i i Sony A7 III
Sony A99 II« »-85/1004.5/54.5/54.5/5 Sep 2016 3,199 i i Sony A99 II
Sony A7R II« »HiRec90/1005/54.5/55/5 Jun 2015 3,199- i Sony A7R II
Sony A7 II« »Rec82/1004.5/55/55/5 Nov 2014 1,999- i Sony A7 II
Sony A7R« »HiRec82/1004.5/55/55/5 Oct 2013 2,299- i Sony A7R

The review scores listed above should be treated with care, though. The assessments were made in relation to similar cameras of the same technological generation. Thus, a score needs to be put into the context of the launch date and the launch price of the camera, and rating-comparisons among cameras that span long time periods or concern very differently equipped models make little sense. It should also be noted that some of the review sites have over time altered the way they render their verdicts.

 

Other camera comparisons

Did this review help to inform your camera decision process? If you would like to see a different side-by-side camera review, just make a corresponding selection in the search boxes below. Alternatively, you can follow any of the listed hyperlinks for comparisons that others found interesting. If you cannot find the camera you are interested in, please contact me, and I will try to add information on that model to the database.

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