Sony Alpha 7R IIIA vs Pentax K-3 Mark III

In this comparison, we will evaluate the Sony Alpha 7R IIIA and the Pentax K-3 Mark III, highlighting the advantages of each over the other, discussing their pros and cons, shared strengths and weaknesses, and providing a rating based on their available features and specifications to assist you in choosing the one that best suits your needs.

Sony Alpha 7R IIIA was introduced in October 2017 and Pentax K-3 Mark III was introduced in March 2021. Let us first list highlights of the models.

Now that we've looked at the most essential specifications and gained a basic understanding of these cameras, we can delve into more details and see the differences between them.

This section shows those features and specifications which are the reason to choose Sony Alpha 7R IIIA over Pentax K-3 Mark III.

This section shows those features and specifications which are the reason to choose Pentax K-3 Mark III over Sony Alpha 7R IIIA.

We already listed pros and cons of each model. However, you may also find useful to look at their common strengths and weaknesses shown side-by-side.

Screen

Sony Alpha 7R IIIA has a 3.0" Tilting screen with 2,360k dot resolution and Pentax K-3 Mark III has a 3.2" Fixed screen with 1,620k dot resolution. Tilting screen makes Sony Alpha 7R IIIA very useful for photography purposes but not so useful for video shooting. Both models feature touchscreen which has advantages such as easy menu navigation, intuitive controls, quick setting adjustment and most importantly a Touch-to-Focus functionality allowing users to select a specific point on the screen where they want the camera to focus. This feature can be helpful for achieving precise focus in both photo and video recording.

Viewfinder

Sony Alpha 7R IIIA has a built-in 0.5" Electronic viewfinder with 3,686k dot resolution and Pentax K-3 Mark III has a built-in Optical (pentaprism) viewfinder. They both have 100% coverage.

Sony Alpha 7R IIIA features a 42.4 megapixel Full Frame BSI-CMOS sensor with dimensions of 35.9 x 24 mm and a total area of 861.6 mm². Its native ISO range is 100 - 32,000 and expands to 50 - 102,400 in boosted mode. Pentax K-3 Mark III features a 25.73 megapixel APS-C CMOS sensor with dimensions of 23.3 x 15.5 mm and a total area of 240.3 mm². Its native ISO range is 100 - 1,600,000.

Sony Alpha 7R IIIA has BSI-CMOS sensor, short for Backside Illuminated Complementary Metal-Oxide-Semiconductor sensor. In traditional CMOS sensors, the wiring and circuitry are located on the front side of the sensor, which can block some of the incoming light. BSI technology flips this design by placing the photosensitive elements (pixels) on the backside of the sensor, allowing more light to reach the pixels. This significantly enhances light sensitivity and improves low-light performance. BSI-CMOS sensors are particularly effective in low-light conditions, as they can capture more light, resulting in brighter and less noisy images. This makes them well-suited for indoor and night photography. BSI-CMOS sensors deliver a higher SNR and reduced cross-talk.

Here is a sensor size comparison chart where you can see how different sensors compare with each other:

Sensor size chart

	Sensor	Dimensions	Area	Aspect Ratio	Crop Factor
	Medium Format	44 x 33 mm	1452 mm2	4:3	0.79x
	Full Frame	36 x 24 mm	864 mm2	3:2	1x
	APS-H	27 x 18 mm	486 mm2	3:2	1.3x
	APS-C	23.6 x 15.6 mm	368.2 mm2	3:2	1.5x
	APS-C (Canon)	22.3 x 14.9 mm	332.3 mm2	3:2	1.6x
	Micro Four Thirds	17.4 x 13 mm	226.2 mm2	4:3	2x
	1-inch	13.2 x 8.8 mm	116.2 mm2	3:2	2.7x
	1/1.7-inch	7.44 x 5.58 mm	41.5 mm2	4:3	4.7x
	1/2.3-inch	6.17 x 4.55 mm	28.1 mm2	4:3	5.6x

Sony Alpha 7R IIIA is equipped with BIONZ X processor and can take pictures up to 7952 x 5304 resolution. Pentax K-3 Mark III is equipped with PRIME V processor and can take pictures up to 6192 x 4128 resolution.

Lens Mount

Sony Alpha 7R IIIA has Sony E lens mount and Pentax K-3 Mark III has Pentax K_AF2 lens mount. Due to Full Frame sensor in Sony Alpha 7R IIIA its crop factor is equal to 1x, this means that a 35mm equivalent focal length of the mounted lens will be equal to its actual focal length. Due to APS-C sensor in Pentax K-3 Mark III its crop factor is equal to 1.5x, this means that a 35mm equivalent focal length of the mounted lens will be equal to its actual focal length times 1.5.

No Low-Pass Filter

There is no optical low-pass filter (OLPF), also known as an anti-aliasing filter, in front of the sensor on either of the cameras. This results in a slightly sharper image but may also introduce moiré patterns and aliasing artifacts when photographing subjects with fine, repetitive patterns or details.

In-Body Image Stabilization

The cameras have a built-in in-body image stabilization (IBIS) with 5.5 stops of compensation. This means that you are still getting vibration reduction when cameras are paired with non-image stabilizied lenses. It also works with lenses with optical image stabilization and in combination can achieve even better compensation.

Built-in Wi-Fi

Cameras have built-in Wi-Fi (802.11b/g/n, 2.4 GHz) which allows to easily transfer photos and videos from the camera to other Wi-Fi-enabled devices, such as smartphones, tablets, printers, or computers. This eliminates the need for cables and allows for quick and convenient media sharing and social media integration. It gives you the ability to control your camera remotely using a smartphone or tablet. This is particularly useful for taking self-portraits, group shots, or capturing images in challenging conditions without having to touch the camera. Firmware updates can also be downloaded and installed wirelessly.
  Check out the cameras in our database that have built-in WiFi.

Bluetooth

Sony Alpha 7R IIIA and Pentax K-3 Mark III have built-in Bluetooth which lets you to connect the camera to a smartphone or a dedicated remote control device. This allows you to remotely trigger the camera, adjust settings and controls remotely through a paired mobile app. While Wi-Fi is generally faster for transferring larger files, Bluetooth can be used for small, selective transfers, it can provide real-time information about your camera's battery status, memory card capacity, and other key settings directly on your paired smartphone or smartwatch.
  Check out the cameras in our database that have built-in Bluetooth.

NFC on Sony Alpha 7R IIIA

Sony Alpha 7R IIIA has Near Field Communication (NFC) technology which simplifies the process of pairing it with other NFC-enabled devices like smartphones or tablets. It allows to quickly transfer photos and videos or remotely control the camera from compatible device. NFC can also be used for authentication and security purposes. It can verify your identity before accessing certain features or transferring sensitive data. It can be used with NFC-enabled accessories as well, such as lenses, flashes and GPS devices.

USB Inputs and HDMI Outputs

Both models have USB 3.2 Gen 1x1 (5 GBit/sec) Type-C inputs for data transfer and battery charging. Sony Alpha 7R IIIA has a Micro HDMI and Pentax K-3 Mark III has a Micro HDMI connector for video signal output.

Battery

Sony Alpha 7R IIIA comes with NP-FZ100 battery pack with battery life of 650 shots and Pentax K-3 Mark III comes with D-LI90 battery pack with battery life of 800 shots.

External Storage Slots

Sony Alpha 7R IIIA has two card slots - one for SD/SDHC/SDXC (UHS-II) and one for SD/SDHC/SDXC/Memory Stick Duo Hybrid (UHS-I). Pentax K-3 Mark III has two card slots - one for SD/SDHC/SDXC (UHS-II) and one for SD/SDHC/SDXC (UHS-I).

Shutter

Sony Alpha 7R IIIA and Pentax K-3 Mark III have Electronic. shutter. Shutter speed can go up to 1/8000 sec on Sony Alpha 7R IIIA, and up to 1/8000 sec on Pentax K-3 Mark III. Sony Alpha 7R IIIA can shoot continuously up to 10.0 fps. Pentax K-3 Mark III can shoot continuously up to 12.0 fps.

Focusing

Sony Alpha 7R IIIA has Fast Hybrid AF (Phase-detection / Contrast-detection) system with 425 focusing points and Pentax K-3 Mark III has 101 (25 cross-type) focusing points. Sony Alpha 7R IIIA has detection range from -2 to +20 EV and Pentax K-3 Mark III has detection range from -4 to +18 EV.

Exposure

Both cameras' exposure metering ranges from -3 to +20 EV and you can set the exposure compensation within the ±5 EV range. You can also do exposure bracketing and manual exposure adjustment on Sony Alpha 7R IIIA and exposure lock, exposure bracketing and manual exposure adjustment on Pentax K-3 Mark III.

Flash

Cameras have no built-in flash but an external flash may be connected to both of them via Intelligent Hot Shoe or PC Terminal to Sony Alpha 7R IIIA and via Hot Shoe or PC Terminal to Pentax K-3 Mark III. The fastest flash synchronization speed is 1/250 sec on Sony Alpha 7R IIIA and 1/200 sec on Pentax K-3 Mark III.

Sony Alpha 7R IIIA body has dimensions of 127 x 96 x 74 mm (5 x 3.78 x 2.91") and Pentax K-3 Mark III body has dimensions of 135 x 104 x 74 mm (5.31 x 4.09 x 2.91"). Sony Alpha 7R IIIA weighs 657 g (1.45 lb / 23.17 oz) and Pentax K-3 Mark III weighs 820 g (1.81 lb / 28.92 oz).

Sony Alpha 7R IIIA

Pentax K-3 Mark III

127 mm

96 mm

135 mm

104 mm

96 mm

104 mm

74 mm

74 mm