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EOS R3 vs EOS-1D X Mark III: How to Decide?

With the release of the EOS R3, there are now two high speed burst-capable professional camera models in the EOS lineup—the EOS R3 and the EOS-1D X Mark III. How are they different, and what should you consider when deciding between the two? Find out in this article.

1. Size and weight
2. Dials and buttons
3. Still image resolution and imaging performance
4. High ISO speed performance
5. Mechanical shutter performance
6. Electronic shutter performance
7. AF performance
8. Image stabilisation
9. Viewfinder
10. Video capabilities


1. Size and weight


The most obvious difference between the EOS R3 and the EOS-1D X Mark III is their size and weight. As a mirrorless camera, the EOS R3 does not require an optical viewfinder or mirror unit, which allows it to be lighter and more compact. Meanwhile, the EOS-1D X Mark III is a DSLR camera, which means it is equipped with a mirror system. Achieving an optical viewfinder with 100% coverage on a full-frame sensor also means that a rather large pentaprism is necessary. The pentaprism is made of glass, which adds to the weight of the EOS-1D X Mark III.

In terms of width, there isn’t much of a difference, with the EOS R3 being only 8mm narrower. However, the 25mm height difference is more obvious, and makes the EOS R3 look more compact in comparison. 


In terms of depth, on paper, the EOS-1D X Mark III appears to be the slimmer camera, with the EOS R3 about 4.6mm thicker. This is because the electronic viewfinder (EVF) on the EOS R3 protrudes more. But measuring just the thickness from the lens mount to the rear of the body, the EOS R3 is slimmer at around 54mm compared to 66mm on the EOS-1D X Mark III. 


Without batteries or memory cards, the EOS R3 weighs around 822g whereas the EOS-1D X Mark III weighs around 1250g. The 428g difference can be quite significant to photographers who use large and heavy lenses such as professional super telephoto lenses.


2. Dials and buttons

No major difference in interface

The EOS R3 and the EOS-1D X Mark III have around the same number of buttons in roughly the same positions. Both also have a touch sensor-controlled Smart Controller on top of the AF-ON button. Whether you are thinking of switching to the EOS R3 from the EOS-1D X Mark III or using both camera models alongside each other, transiting should be quite seamless where interface and operations are concerned.

EOS R3: Important buttons right under your thumb

What is different: the WB and ISO speed setting buttons on the top panel of the EOS-1D X Mark III are not present on the EOS R3. Instead, the EOS R3 has a second sub-electronic dial right under your thumb. In fact, the important rear buttons are now located within an easier thumb’s reach away while you’re holding the camera with your right hand—good news for users with smaller hands.


3. Still image resolution and imaging performance

Megapixels and mount

The EOS R3 has around 4 effective megapixels more than the EOS-1D X Mark III. It is also equipped with the RF mount, which enables higher edge to edge image quality, promising visual resolution that goes beyond what the pixel count suggests. However, it is also worth noting that many sports photographers and photojournalists still use the EOS-1D X Mark III. 20.1 effective megapixels is sufficient for making commercial A3-size prints. 

Improved HDR mode that supports HDR PQ HEIF bracketing

Both the EOS-1D X Mark III and the EOS R3 support shooting HDR PQ images in 10-bit HEIF format. On the EOS R3, this extends to the HDR mode, which shoots and merges three exposure bracketed shots:  you can choose to take and record the shots in HDR PQ HEIF format to achieve even wider dynamic range.

Regardless of whether you record in JPEG or HDR PQ HEIF, the EOS R3 records the bracketed shots at a higher speed—as fast as 0.02 seconds. This helps to further reduce the chances of subject blur and camera shake, even when shooting handheld. 

The EOS R3 also supports focus bracketing, making it possible to create focus-stacked images.


4. High ISO speed performance

Native ISO 102,400
Expanded ISO 204,800
Low light AF limit: EV -7.5
Native ISO 102,400
Expanded ISO 819,200
Low light AF limit: EV -6

Same native ISO speed, but different expanded ISO speeds and low light AF limits

The EOS-1D X Mark III and the EOS R3 have the same maximum native ISO speed of 102,400. At such high ISO speeds, noise is unavoidable, but will not be prominent in smaller-sized prints and display formats. The higher maximum native ISO speed has also raised overall high ISO performance—ISO 6400 results in relatively clean images on both cameras. This offers quite a bit of flexibility for situations where you need to use a faster speed to freeze subjects or avoid camera shake when shooting in low-light conditions.


EOS R3: ISO 102,400

EOS-1D X Mark III: ISO 102,400


EOS-1D X Mark III: ISO 409,600

Usually, if two cameras have the same sensor size (e.g. full-frame sensor), the one with fewer pixels will have better high ISO speed performance. However, the EOS R3 adopts a newly developed back-illuminated stacked CMOS image sensor, which not only achieves the same native ISO speed as the EOS-1D X Mark III, but also expands the low light AF limit to EV -7.5.

At the same time, the expanded ISO speed setting on the EOS-1D X Mark III goes as high as ISO 819,200, ready for those situations where you need that capability to nail the shot, regardless of the image noise. Such potential is the strength of the EOS-1D X Mark III.


5. Mechanical shutter performance

When you want faster high-speed bursts without any rolling shutter

The EOS-1D X Mark III has the faster mechanical shutter, supporting a maximum continuous shooting speed of 16 fps compared to the 12 fps on the EOS R3. Using the mechanical shutter to capture fast-moving subjects helps to avoid rolling shutter distortion, which is likely to occur with an electronic shutter. If you want to shoot high-speed bursts with absolutely no risk of rolling shutter, the EOS-1D X Mark III holds the advantage.

Also see:
Shutter Modes & Continuous Shooting Modes: When to Use Which?


6. Electronic shutter performance


Shutter speed and continuous shooting speed

The faster readout speed of the EOS R3’s new back-illuminated stacked CMOS image sensor resulted in a dramatic improvement in its electronic shutter capabilities:
- Continuous shooting can be as fast as up to 30 fps, although the actual shooting speed depends on your settings and shooting conditions
- Significantly reduced rolling shutter distortion
- A shutter speed of up to 1/64,000 sec

On the other hand, the EOS-1D X Mark III can shoot up to 20 fps during Live View shooting, although that means you won’t be using the viewfinder.

The moment a water balloon bursts, captured at 1/64000 sec on the EOS R3. The EOS R3 takes the ability to capture instances to a whole new level.

Flash photography during with the electronic shutter

A slower image sensor readout during electronic shutter shooting also causes black bands on the image during flash photography. The EOS-1D X Mark III doesn’t support flash photography during electronic shutter shooting, but the EOS R3 does.


7. AF performance

Professional cameras are often used to shoot action in scenes such as sports and wildlife, which is why the autofocusing (AF) performance is one aspect to pay attention to when deciding on a camera.

OVF means separate AF sensor

During optical viewfinder (OVF) shooting on the EOS-1D X Mark III, autofocusing is carried out via a separate AF sensor that conducts highly precise phase detection AF. During Live View shooting, autofocusing is carried out by the Dual Pixel CMOS AF system, which conducts image-plane phase difference detection using the image sensor pixels.

On the other hand, during EVF shooting on a mirrorless camera like the EOS R3, the image display on the EVF is basically the same as the Live View display, so the Dual Pixel CMOS AF can be used for both. (Also see: 9. Viewfinder)


The dedicated AF sensor on the EOS-1D X Mark III

The AF sensor on the EOS-1D X Mark III has 191 AF points that cover the area shown in red above. Of these, 155 points are cross-type sensors that can detect on both the horizontal and vertical axes, achieving good precision. This is a system that is sufficient for most compositions.

The AF tracking system during continuous shooting has also been polished over the years through feedback from professional photographers, and thus is performance guaranteed. Furthermore, the camera is equipped with the EOS iTR AF X subject detection and tracking system, which detects and tracks subjects’ faces and heads as well as colours, and shapes for greater accuracy and precision. However, it is unable to detect eyes, making this possible only during Live View shooting with Dual Pixel CMOS AF.

Comparing subject detection capabilities

Eyes/ Face/ Head/ Body
Face/ Head (Eyes: Only during Live View shooting)
Dogs, cats, birds
Eyes/ Face/ Body
(cars, motorcycles)
Vehicle body/Helmet

AF on the EOS R3

On the EOS R3, Dual Pixel CMOS AF is used for autofocusing during both viewfinder and Live View shooting. When using a mode that supports subject detection, the EOS iTR AF X system detects subjects over an AF area that covers 100% × 100% (horizontal × vertical) of the image frame. When not conducting subject detection, the AF area covers 90% × 100% (horizontal × vertical) of the image frame.

Also see: Is Composition Easier on a Mirrorless Camera?

Advanced AF features

While both the EOS R3 and the EOS-1D X Mark III use the DIGIC X image processing engine, the EOS R3 has significantly more advanced subject detection capabilities due to deep learning technology. It is also equipped with advanced AF control features such as Eye Control AF. These mean that the camera and achieve precise autofocusing on its own without the need for much input from the user.

How much control do you want?

A camera’s AF system is linked to many other features, but to sum up, the AF on the EOS-1D X Mark III is built to respond to a photographer’s technique, whereas on the smart AF on the EOS R3, influenced by advanced automation, built to reduce the burden of operation on the photographer.


8. Image stabilisation

The EOS R3 features a built-in sensor-based In-Body Image Stabilizer (In-Body IS), which performs 5-axis image stabilisation. When an RF lens with the Optical Image Stabilizer (Optical IS) is attached, these in-lens and in-camera image stabilisation systems work together as one Coordinated Control IS system to achieve a stronger image stabilisation effect, correcting camera shake by up to 8 shutter speed stops’ equivalent.

- In-Body IS: Up to 8 stops
- Coordinated Control IS
(when combined with Optical IS)
Optical IS only

Focal length matters

Generally, In-Body IS is better at correcting the camera shake that occurs when shooting at wider angles, whereas Optical IS is good at correcting camera shake at long focal lengths. Therefore, when shooting with telephoto lenses, In-Body IS and Coordinated Control IS provide limited advantage over Optical IS alone. If you mainly shoot 200mm and above, the EOS-1D X Mark III would be sufficient.

However, if you mostly shoot portraiture or other subjects that call for focal lengths in the standard to medium telephoto focal length, you would benefit greatly from In-Body IS on the EOS R3, especially if you use lenses with no Optical IS such as the 50mm f/1.2 and 85mm f/1.2 lenses.

Image stabilisation effect when using EOS R3 with key RF lenses

Coordinated Control IS
Max. IS effect in stops (CIPA standards)
RF24-105mm f/4L IS USM
RF50mm f/1.2L USM
RF24-70mm f/2.8L IS USM
RF15-35mm f/2.8L IS USM
RF70-200mm f/2.8L IS USM
RF100-500mm f/4.5-7.1L IS USM
RF85mm f/1.2L USM


9. Viewfinder

The viewfinders on both cameras provide the same coverage and magnification, so it ultimately boils down to whether you prefer an EVF (EOS R3) or optical viewfinder (EOS-1D X Mark III).

Viewfinder type
EVF / 5.76 million dot OLED
OVF/ Pentaprism
approx. 0.76x
approx. 0.76x
approx. 23mm
approx. 20mm

An EVF works by projecting the Live View image onto an OLED panel in the viewfinder.  Some photographers will therefore be understandably concerned about the display time lag compared to an OVF, which provides a direct view of the scene.

The EOS R3’s 5.76 million dot ultra-high-definition OLED panel is capable of displaying images at up to 119.88 fps, which results in a seamless, natural view. In addition, just like the Live View image, the EVF image also reflects the effects of exposure, white balance, and Picture Style settings so that you can see and adjust them as you shoot. You can even check how the bokeh will look, whereas you can’t on an OVF.

OVF view assist to simulate the OVF look

For those concerned about tones, the EOS R3 is equipped with the OVF Simulation View Assist feature, which uses HDR technology to display a viewfinder image with a dynamic range and tones similar to those on an OVF.

Merits of an OVF

As a feature on a professional-grade camera, the OVF on the EOS-1D X Mark III is the product of years of continuous improvement, and therefore can be said to provide the highest performance standard that an OVF can provide. The optical display gives zero time lag, something that photographers who place utmost importance on shutter release timing might consider non-negotiable. Looking through an OVF for long durations is also less tiring on the eyes compared to on an EVF.


There are sound reasons for wanting an OVF, and if those are crucial to you, the EOS-1D X Mark III is the obvious choice. But an EVF also has its benefits, and with the EOS R3, you get to enjoy the benefits of the newest technology.

Also see:
Camera Basics #12: The Viewfinder
Lens FAQ #2: Can A Fast Lens Really Make It Easier To See Through The Viewfinder?


10. Video capabilities

6K RAW vs 5.5K RAW: does it really make that much of a difference?

The maximum video recording quality on each camera is as follows:
EOS R3: 6K RAW 59.94/50.00 fps
EOS-1D X Mark III: 5.5K RAW 59.94/50.00 fps

When viewed directly, as there isn’t much difference between 6K and 5.5K. In fact, those recording formats are meant to be either to achieve higher quality oversampled 4K video, or cropped for creative purposes in 4K video production. Of course, the higher 6K resolution on the EOS R3 means additional flexibility for cropping, but as the diagram below shows, probably not as much as you might think.

High frame rate shooting

Both cameras support both the 4K DCI and 4K UHD formats, and both can produce higher quality 4K video by utilising the maximum recording resolution for oversampling. The main difference lies in the High Frame Rate modes: The EOS R3 can shoot both 4K UHD and Full HD video at 119.88/100.00 fps, but the EOS-1D X Mark III can do so only in Full HD format.

Maximum resolution
6K RAW 59.94/50.00fps
5.5K RAW 59.94/50.00fps
High Frame Rate
4K UHD 119.88/100.00fps
FHD 119.88/100.00fps
FHD 119.88/100.00fps
Canon Log 3
Canon Log


HDR capabilities

The EOS-1D X Mark III supports only Canon Log (dynamic range: approximately 800% at ISO 400 or higher), whereas the EOS R3 supports both Canon Log 3 and HDR PQ.

Canon Log 3 achieves a dynamic range of up to 1600% while retaining Canon Log’s advantages for colour grading. Meanwhile, HDR PQ is a HDR standard that is increasingly used in cinema and online videos. If you have a HDR PQ-ready monitor, you can even view HDR videos shot in HDR PQ mode without having to colour grade them first.

Continuous recording time

Another aspect that sets the two cameras apart is the continuous recording time for video. On paper, the video recording limit of the EOS-1D X Mark III is 30 minutes, whereas that of the EOS R3 is 6 hours for normal video, and up to 1 hour 30 minutes for high frame rate video. In actual use, the shooting duration depends on the camera’s heating situation, but we can conclude that the EOS R3 is capable of shooting video for a longer duration.


In conclusion

As the third generation of the top-of-the-line EOS-1D X series, which is associated with the epitome of Canon’s DSLR technology, the EOS-1D X Mark III is built for ultimate responsiveness to a seasoned professional photographer’s instincts and techniques. Meanwhile, as the first professional-grade camera in the EOS R lineup, the EOS R3 is a smart camera that boasts the advantages of cutting-edge mirrorless camera technology, including the new RF mount which enables better optical quality.

The cameras may be equipped with slightly different features and technologies, but both are designed to ensure reliability, durability, and performance even under the challenging conditions encountered in wildlife, sports, and news photography. Whichever you eventually choose, you can be assured of its professional-grade quality. 


USD 5,999
USD 6,499


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