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Pentax 645D versus Sony A7R III

The Pentax 645D and the Sony Alpha A7R III are two digital cameras that were officially introduced, respectively, in March 2010 and October 2017. The 645D is a DSLR, while the A7R III is a mirrorless interchangeable lens camera. The cameras are based on a medium format (645D) and a full frame sensor. The Pentax has a resolution of 39.5 megapixel, whereas the Sony provides 42.2 MP.

Body comparison

The physical size and weight of the Pentax 645D and the Sony A7R III are illustrated in the side-by-side display below. Three consecutive views from the front, the top, and the rear side are shown. All width, height and depth dimensions are rounded to the nearest millimeter. You can also toggle the display 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 645D – represents the basis for the calculations across all the size and weight measures).

Pentax 645D vs Sony A7R III front
645D versus A7R III top view
645D and A7R III rear side
Body view (645D on the left)

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 notably smaller (33 percent) than the Pentax 645D. Moreover, the A7R III is substantially lighter (56 percent) than the 645D. 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 table below summarizes the key physical specs of the two cameras alongside a broader set of comparators. 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 comparisons there.

Camera Body Specifications
Camera Camera
Width
Camera
Height
Camera
Depth
Camera
Weight
Battery
Life
(CIPA)
Weather
Sealing
(y/n)
Camera
Launch
(year)
Launch
Price
(USD)
Street
Price
(amazon)
Used
Price
(ebay)
Pentax 645D (⇒ rgt) 156 mm 117 mm 119 mm 1480 g .. YES 2010 9,995discont. check
Sony A7R III (⇒ lft) 127 mm 96 mm 74 mm 650 g 650 YES 2017 3,199 latest check
Canon 1D X Mark II (⇒ lft | rgt) 158 mm 168 mm 83 mm 1530 g 1210 YES 2016 5,999 latest check
Canon 1D X (⇒ lft | rgt) 158 mm 168 mm 83 mm 1551 g 1120 YES 2011 6,799discont. check
Canon 1D Mark IV (⇒ lft | rgt) 156 mm 157 mm 80 mm 1230 g 1500 YES 2009 4,999discont. check
Leica S Typ 006 (⇒ lft | rgt) 160 mm 120 mm 80 mm 1260 g .. YES 2012 21,950discont. check
Nikon D850 (⇒ lft | rgt) 146 mm 124 mm 79 mm 1005 g 1840 YES 2017 3,299 latest check
Nikon D5 (⇒ lft | rgt) 160 mm 159 mm 92 mm 1415 g 3780 YES 2016 6,499 latest check
Nikon D810 (⇒ lft | rgt) 146 mm 123 mm 82 mm 980 g 1200 YES 2014 3,299discont. check
Nikon D3S (⇒ lft | rgt) 160 mm 157 mm 88 mm 1240 g 4200 YES 2009 5,199discont. check
Pentax 645Z (⇒ lft | rgt) 156 mm 117 mm 123 mm 1550 g 650 YES 2014 8,499 latest check
Sony A99 II (⇒ lft | rgt) 143 mm 104 mm 76 mm 849 g 490 YES 2016 3,199 latest check
Sony A7R II (⇒ lft | rgt) 127 mm 96 mm 60 mm 625 g 290 YES 2015 3,199discont. check
Sony A7S II (⇒ lft | rgt) 127 mm 96 mm 60 mm 627 g 370 YES 2015 2,999 latest check
Sony A7 II (⇒ lft | rgt) 127 mm 96 mm 60 mm 599 g 350 YES 2014 1,999 latest check
Sony A7R (⇒ lft | rgt) 127 mm 94 mm 48 mm 465 g 340 YES 2013 2,299discont. check

The listed 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 68 percent) than the 645D, 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. Then, after the new model is out, very good deals can frequently be found on the pre-owned market.

Sensor comparison

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. Further, a large sensor camera will give the photographer additional creative options when using shallow depth-of-field to isolate a subject from its background. On the downside, larger sensors tend to be associated with larger, more expensive camera bodies and lenses.

Of the two cameras under consideration, the Pentax 645D features a medium format sensor and the Sony A7R III a full frame sensor. The sensor area in the A7R III is 41 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 645D has a native 4:3 aspect ratio, while the one in the A7R III offers a 3:2 aspect.

Pentax 645D and Sony A7R III sensor measures
Sensor size

Despite having a smaller sensor, the A7R III offers a slightly higher resolution of 42.2 megapixel, compared with 39.5 MP of the 645D. This megapixel advantage comes at the cost of a higher pixel density and a smaller size of the individual pixel (with a pixel pitch of 4.52μm versus 6.06μm for the 645D). However, it should be noted that the A7R III is much more recent (by 7 years and 7 months) than the 645D, and its sensor will have benefitted from technological advances during this time that make it possible to gather light more efficiently. 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 645D, 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).

645D versus A7R III MP
Sensor resolution

Since 2007, DXO Mark has published sensor performance measurements that have been derived using a consistent methodology. This service assesses and scores the color depth ("DXO Portrait"), dynamic range ("DXO Landscape"), and low-light sensitivity ("DXO Sports") of camera sensors, and also publishes an overall camera score. Of the two cameras under consideration, the A7R III offers substantially better image quality than the 645D (overall score 18 points higher). The advantage is based on 1.4 bits higher color depth, 2.1 EV in additional dynamic range, and 1.5 stops in additional low light sensitivity. The adjacent table reports on the physical sensor characteristics and the outcomes of the DXO sensor quality tests for a sample of comparator-cameras.

Sensor Characteristics
Camera Sensor
Class
Resolution
(Megapixel)
Horiz.
Pixels
Vert.
Pixels
Video
Format
DXO
Portrait
DXO
Landscape
DXO
Sports
DXO
Overall
Pentax 645D (⇒ rgt) Medium Format 39.5 7264 5440 no 24.6 12.6 1262 82
Sony A7R III (⇒ lft) Full Frame 42.2 7952 5304 4K/30p 26.0 14.7 3523 100
Canon 1D X Mark II (⇒ lft | rgt) Full Frame 20.0 5472 3648 4K/60p 24.1 13.5 3207 88
Canon 1D X (⇒ lft | rgt) Full Frame 17.9 5184 3456 1080/30p 23.8 11.8 2786 82
Canon 1D Mark IV (⇒ lft | rgt) APS-H 16.0 4896 3264 1080/30p 22.8 12.0 1320 74
Leica S Typ 006 (⇒ lft | rgt) Medium Format 37.5 7500 5000 no 23.9 12.2 824 76
Nikon D850 (⇒ lft | rgt) Full Frame 45.4 8256 5504 4K/30p 26.4 14.8 2660 100
Nikon D5 (⇒ lft | rgt) Full Frame 20.7 5588 3712 4K/30p 25.1 12.3 2343 88
Nikon D810 (⇒ lft | rgt) Full Frame 36.2 7360 4912 1080/60p 25.7 14.8 2853 97
Nikon D3S (⇒ lft | rgt) Full Frame 12.1 4256 2832 720/24p 23.5 12.0 3253 82
Pentax 645Z (⇒ lft | rgt) Medium Format 51.1 8256 6192 1080/60i 26.0 14.7 4505 101
Sony A99 II (⇒ lft | rgt) Full Frame 42.2 7952 5304 4K/30p 25.4 13.4 2317 92
Sony A7R II (⇒ lft | rgt) Full Frame 42.2 7952 5304 4K/30p 26.0 13.9 3434 98
Sony A7S II (⇒ lft | rgt) Full Frame 12.0 4240 2832 4K/30p 23.6 13.3 2993 85
Sony A7 II (⇒ lft | rgt) Full Frame 24.0 6000 4000 1080/60p 24.9 13.6 2449 90
Sony A7R (⇒ lft | rgt) Full Frame 36.2 7360 4912 1080/60p 25.6 14.1 2746 95

Many modern cameras are not only capable of taking still images, but can also record movies. The A7R III indeed provides for movie recording, while the 645D does not. The highest resolution format that the A7R III can use is 4K/30p.

Feature comparison

Apart from body and sensor, cameras can and do differ across a variety of features. For example, the A7R III has an electronic viewfinder (3686k dots), while the 645D 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 following table reports on some other key feature differences and similarities of the Pentax 645D, the Sony A7R III, and comparable cameras. If needed, the dpreview camera hub, for example, contains further detail on the cameras' specs.

Core Features
Camera Viewfinder
(Type or
'000 dots)
Control
Panel
(Y/n)
LCD
Size
(inch)
LCD
Resolution
('000 dots)
LCD
Attach-
ment
Touch
Screen
(Y/n)
Shutter
speed
(1/sec)
Shutter
flaps
(1/sec))
Build-in
Flash
(GN)
Build-in
Image
Stab
Pentax 645D (⇒ rgt) optical YES 3.0 921 fixed no 4000 1.1 no no
Sony A7R III (⇒ lft) 3686 no 3.0 1440 tilting YES 8000 10.0 no YES
Canon 1D X Mark II (⇒ lft | rgt) optical YES 3.2 1620 fixed YES 8000 16.0 no no
Canon 1D X (⇒ lft | rgt) optical YES 3.2 1040 fixed no 8000 14.0 no no
Canon 1D Mark IV (⇒ lft | rgt) optical YES 3.0 920 fixed no 8000 10.0 no no
Leica S Typ 006 (⇒ lft | rgt) optical YES 3.0 922 fixed no 4000 1.5 no no
Nikon D850 (⇒ lft | rgt) optical YES 3.2 2359 tilting YES 8000 9.0 no no
Nikon D5 (⇒ lft | rgt) optical YES 3.2 2359 fixed YES 8000 14.0 no no
Nikon D810 (⇒ lft | rgt) optical YES 3.2 1229 fixed no 4000 5.0 12 no
Nikon D3S (⇒ lft | rgt) optical YES 3.0 921 fixed no 8000 11.0 no no
Pentax 645Z (⇒ lft | rgt) optical YES 3.2 1037 tilting no 4000 3.0 no no
Sony A99 II (⇒ lft | rgt) 2400 YES 3.0 1229 tilting no 8000 12.0 no YES
Sony A7R II (⇒ lft | rgt) 2400 no 3.0 1229 tilting no 8000 5.0 no YES
Sony A7S II (⇒ lft | rgt) 2400 no 3.0 1229 tilting no 8000 5.0 no YES
Sony A7 II (⇒ lft | rgt) 2400 no 3.0 1230 tilting no 8000 5.0 no YES
Sony A7R (⇒ lft | rgt) 2400 no 3.0 1230 tilting no 8000 4.0 no no

The A7R III is a current model that online retailers, such as amazon, will have in stock. In contrast, the 645D has been discontinued (but it can be found pre-owned on ebay). As a replacement in the same line of cameras, the 645D was succeeded by the Pentax 645Z.

Summary

So how do things add up? Is the Pentax 645D 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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Arguments in favor of the Pentax 645D:

  • Brighter framing: Features an optical viewfinder for clear, lag-free composition.
  • Easier setting verification: Has an LCD display on top to control shooting parameters.
  • More heavily discounted: Has been available for much longer (launched in March 2010).

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Reasons to prefer the Sony Alpha A7R III:

  • More detail: Has more megapixels (42.2 vs 39.5MP), which boosts linear resolution by 5%.
  • High quality composites: Can combine several shots after pixel-shifting its sensor.
  • Better image quality: Scores substantially higher (18 points) in the DXO overall evaluation.
  • Richer colors: Generates noticeably more natural colors (1.4 bits more color depth).
  • More dynamic range: Captures a broader range of light and dark details (2.1 EV of extra DR).
  • Better low-light sensitivity: Can shoot in dim conditions (1.5 stops ISO advantage).
  • Broader imaging potential: Can capture not only stills but also 4K/30p video.
  • More framing info: Has an electronic viewfinder that displays shooting data.
  • More detailed LCD: Has a higher resolution rear screen (1440k vs 921k dots).
  • More flexible LCD: Has a tilting screen for odd-angle shots in landscape orientation.
  • 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 1.1 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 830g or 56 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 (68 percent cheaper at launch).
  • More modern: Reflects 7 years and 7 months of technical progress since the 645D launch.

If the count of relative strengths (bullet points above) is taken as a measure, the A7R III is the clear winner of the contest (19 : 3 points). However, the relevance of individual strengths will vary across photographers, so that you might want to apply your own weighing scheme to the summary points.

645D 03:19 A7R III

In any case, while the comparison of technical specifications can provide a useful overview of the capabilities of different cameras, it remains partial and cannot reveal, for example, the handling experience and imaging performance when actually working with the 645D or the A7R III. User reviews, such as those found at amazon, can sometimes inform about these issues, but such feedback is often incomplete, inconsistent, and biased. This is why hands-on reviews by experts are important. The table below summarizes the assessments of some of the best known camera review sites. The full reviews are available, respectively, at cameralabs.com, dpreview.com, ephotozine.com, imaging-resource.com, and photographyblog.com.

Review scores
Camera camera
labs
dp
review
ephoto
zine
imaging
resource
photography
blog
Camera
Launch
(year)
Launch
Price
(USD)
Street
Price
(amazon)
Used
Price
(ebay)
Pentax 645D (⇒ rgt) - - - 4.5/5 - 2010 9,995discont. check
Sony A7R III (⇒ lft) HiRec 90/100 Gold .. .. .. 2017 3,199 latest check
Canon 1D X Mark II (⇒ lft | rgt) - 89/100 Gold 4.5/5 5/5 4.5/5 2016 5,999 latest check
Canon 1D X (⇒ lft | rgt) - - 4.5/5 4.5/5 4.5/5 2011 6,799discont. check
Canon 1D Mark IV (⇒ lft | rgt) - 89/100 Gold - 5/5 - 2009 4,999discont. check
Leica S Typ 006 (⇒ lft | rgt) - - - - - 2012 21,950discont. check
Nikon D850 (⇒ lft | rgt) HiRec 89/100 Gold 4.5/5 .. 5/5 2017 3,299 latest check
Nikon D5 (⇒ lft | rgt) - 89/100 Gold 4.5/5 5/5 5/5 2016 6,499 latest check
Nikon D810 (⇒ lft | rgt) - 86/100 Gold 5/5 4.5/5 4.5/5 2014 3,299discont. check
Nikon D3S (⇒ lft | rgt) - 89/100 Gold 4.5/5 5/5 5/5 2009 5,199discont. check
Pentax 645Z (⇒ lft | rgt) - - 4.5/5 5/5 5/5 2014 8,499 latest check
Sony A99 II (⇒ lft | rgt) - 85/100 Silver 4.5/5 4.5/5 4.5/5 2016 3,199 latest check
Sony A7R II (⇒ lft | rgt) HiRec 90/100 Gold 5/5 4.5/5 5/5 2015 3,199discont. check
Sony A7S II (⇒ lft | rgt) Rec - 4.5/5 5/5 5/5 2015 2,999 latest check
Sony A7 II (⇒ lft | rgt) Rec 82/100 Silver 4.5/5 5/5 5/5 2014 1,999 latest check
Sony A7R (⇒ lft | rgt) HiRec 82/100 Gold 4.5/5 5/5 5/5 2013 2,299discont. check

The review scores listed above should be treated with care, though. The ratings were established in reference to similarly priced cameras that were available in the market at the time of the review. Hence, a score should always be seen in the context of the camera's market launch date and its price, 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 comparisons

In case you would like to check on the differences and similarities of other camera models, just make your choice using the following search menu. There is also a set of direct links to comparison reviews that other users of the CAM-parator app explored. If you cannot find the camera you are interested in, kindly get in touch, and I will try to update the database with the necessary infos.

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