Canon EOS R6 vs R6 Mark III: FPS and Buffer Explained
Canon EOS R6 vs R6 Mark III: FPS, Buffer & Data Throughput
Canon EOS R6 vs R6 Mark III: explore FPS, buffer, sensor data, processing and storage to understand the evolution of high-speed mirrorless photography.
E-E-A-T / First-hand photographic perspective: This educational comparison examines the Canon EOS R6 and EOS R6 Mark III from the perspective of practical digital photography and high-speed image capture. Rather than treating frames per second as an isolated specification, it considers the relationship between sensor resolution, electronic capture, image processing, buffer capacity, C-RAW, memory-card performance and sustained shooting. The discussion is particularly relevant to action and Birds in Flight photography, where the ability to capture and manage large sequences of images can directly influence photographic opportunities.
From FPS to Data Throughput
When photographers compare two generations of mirrorless cameras, frames per second is usually one of the first specifications they look at. The Canon EOS R6, for example, established itself as a remarkably capable high-speed full-frame camera with electronic shooting at up to 20 frames per second. The EOS R6 Mark III raises that headline figure to 40 frames per second.
At first glance, this appears to be a simple case of the newer camera being twice as fast.
It is not quite that simple.
The more interesting way to understand the evolution from the EOS R6 to the EOS R6 Mark III is to move beyond frames per second and consider data throughput.
A modern mirrorless camera is not simply taking photographs. It is continuously moving enormous quantities of information through an imaging pipeline. Light reaches the sensor, the sensor generates image data, that information is read from the sensor, processed, temporarily stored in memory, converted into the selected recording format and eventually written to a memory card.
The practical speed of the camera is therefore determined by much more than its maximum frame rate.
The progression from the EOS R6 to the EOS R6 Mark III provides an excellent illustration of this evolution.
FPS is only the beginning
The original EOS R6 has an approximately 20.1-megapixel full-frame sensor and can shoot at up to approximately 12 fps using its mechanical or electronic first-curtain shutter, and up to approximately 20 fps using the electronic shutter. Canon specifies a maximum RAW burst of approximately 110 frames with a standard card and approximately 240 frames with a high-speed UHS-II card under its specified testing conditions.
The EOS R6 Mark III moves to an approximately 32.5-megapixel full-frame sensor. Its maximum mechanical and electronic first-curtain rate remains approximately 12 fps, but its electronic shutter can reach approximately 40 fps in High-speed continuous shooting+. It also provides an electronic 20 fps High-speed continuous shooting mode.
The headline comparison therefore looks straightforward:
EOS R6: 20 fps electronic
EOS R6 Mark III: 40 fps electronic
But the R6 Mark III is not simply producing twice as many frames. Each frame contains substantially more information.
That is where the comparison becomes much more interesting.
The sensor is generating more information
The EOS R6 produces approximately 20.1 megapixels per full-resolution image, whereas the R6 Mark III produces approximately 32.5 megapixels.
The increase is approximately 62 percent in pixel count.
Now consider the cameras at their maximum electronic frame rates.
The R6 is theoretically moving information corresponding to approximately:
20.1 MP × 20 frames/sec = 402 million pixels/sec
The R6 Mark III is theoretically moving:
32.5 MP × 40 frames/sec = 1.30 billion pixels/sec
These figures are not Canon's specification for an internal data bus and should not be interpreted as such. They are simply a useful way of visualising the scale of the imaging workload.
Nevertheless, the comparison is revealing.
At maximum electronic shooting rate, the R6 Mark III is dealing with more than three times as many image pixels per second as the original R6.
This is why describing the R6 Mark III simply as a “40 fps camera” understates the technological progression.
The RAW file tells another part of the story
The difference becomes even clearer when we look at actual file sizes.
Canon specifies an approximately 21.8 MB RAW file for the EOS R6 and approximately 34.3 MB for the EOS R6 Mark III. C-RAW is approximately 11.2 MB on the R6 and approximately 16.8 MB on the R6 Mark III.
Again, the important point is not simply that the newer camera produces larger files.
It is that the camera is capable of capturing those larger files at substantially higher rates.
A rough multiplication illustrates the scale:
R6 RAW: 21.8 MB × 20 fps ≈ 436 MB/sec
R6 Mark III RAW: 34.3 MB × 40 fps ≈ 1,372 MB/sec
These are illustrative calculations rather than claims about the camera's actual sustained card-writing speed. The camera does not simply write every RAW file directly to the card at that rate. Instead, the data moves through the camera's internal processing and buffer architecture before being written to storage.
But the calculation gives us a useful conceptual understanding.
The R6 Mark III is potentially generating a very large amount of image data in a very short period.
This is where the buffer becomes important
The buffer is essentially the camera's temporary workspace.
When a photographer presses the shutter and maintains a high-speed burst, the camera cannot necessarily write every individual frame to the memory card at exactly the same moment it is being captured.
Instead, image data can accumulate in internal memory while the camera continues processing and writing information to the card.
This creates a fundamental relationship:
Capture speed → Processing → Buffer → Card writing
If capture is faster than the camera can ultimately write to storage, the buffer begins to fill.
Once the available buffer space becomes exhausted, the camera must slow down or temporarily stop shooting while sufficient data is transferred out of the buffer.
This is why buffer capacity cannot be understood independently from file size and memory-card performance.
The R6's published figures are approximately 110 RAW frames with a standard card and 240 RAW frames with a high-speed UHS-II card, while C-RAW can extend the sequence substantially.
The R6 Mark III specifies approximately 34.3 MB RAW files and Canon's published maximum-burst figures vary according to the recording medium and shooting mode. With Canon's specified CFexpress testing card, the camera is capable of very large sequences; with SD cards, the maximum sequence can be considerably more constrained.
This immediately demonstrates an important principle:
A fast camera also needs a fast storage system.
The memory-card interface changes the equation
The original EOS R6 uses UHS-II SD cards.
The EOS R6 Mark III introduces a fundamentally different storage configuration: CFexpress Type B in Slot 1 and UHS-II SD in Slot 2. Canon specifies support for CFexpress 2.0 and VPG400 in the CFexpress slot.
This is particularly significant for sustained high-speed photography.
A CFexpress Type B card provides a much higher-performance storage pathway than a conventional SD card. That gives the camera a more capable route for emptying its internal buffer during demanding high-speed sequences.
Consequently, the memory card is no longer simply a place where photographs are stored after the important work has finished.
In a high-performance mirrorless camera, the card is part of the overall data-throughput system.
Processing speed is more than DIGIC X
Both generations are based around Canon's DIGIC X processing architecture, but it would be misleading to conclude that the two cameras therefore have essentially the same processing capability.
A camera's effective processing performance is determined by the interaction between the processor, sensor architecture, sensor readout, internal memory, firmware, image-processing algorithms, autofocus system and storage interface.
The R6 Mark III combines its processor with a considerably higher-resolution sensor and a much higher maximum electronic shooting rate.
That means the important technological progression is not simply:
older processor → newer processor
It is closer to:
sensor + readout + processor + memory + firmware + buffer + storage
working together as a much more capable imaging system.
This is an important distinction when discussing modern mirrorless cameras.
Why sensor readout matters
Electronic shutter photography does not work in exactly the same way as a conventional mechanical shutter.
The sensor is effectively being read electronically, and the speed with which that information can be collected contributes to the camera's ability to produce high-speed sequences.
This is particularly important because the R6 Mark III can produce 40 fps electronically while simultaneously providing substantially higher resolution than the original R6.
The photographer therefore benefits not merely from a faster sequence, but from a greater ability to sample a rapidly changing subject at very short intervals.
At 20 fps, the theoretical interval between frames is approximately 50 milliseconds.
At 40 fps, it is approximately 25 milliseconds.
That difference can become meaningful when photographing a bird changing wing position, a subject taking off, or a rapidly changing moment in a sporting or action sequence.
But 40 fps does not mean everything is twice as fast
This is perhaps the most important point of the comparison.
The EOS R6 Mark III's 40 fps figure should not be interpreted as meaning that every operation inside the camera is twice as fast as it was in the EOS R6.
It does not mean that:
autofocus is simply twice as fast;
RAW files are written to the card twice as fast;
the buffer is twice as large;
images are transferred to a computer twice as fast;
Lightroom will process the resulting files twice as fast; or
every lens will necessarily maintain 40 fps in every situation.
Canon itself notes that the R6 Mark III's maximum continuous shooting speed can be reduced by factors including Servo AF operation, lens compatibility, aperture changes, zooming, battery condition, temperature, flickering light and other shooting conditions.
This is why “maximum fps” should be regarded as a peak system capability, rather than a universal measurement of camera speed.
C-RAW provides another useful example
The comparison also helps explain why C-RAW is more interesting than simply calling it a “smaller RAW file.”
The R6's C-RAW file is approximately 11.2 MB, while the R6 Mark III's C-RAW file is approximately 16.8 MB.
The smaller file size reduces the amount of storage required and can allow significantly longer bursts.
But C-RAW does not eliminate the imaging workload created by the sensor.
The camera still has to capture the information from the sensor and process it into the selected C-RAW representation.
C-RAW therefore becomes part of the camera's overall data-management strategy.
For photographers working with large numbers of high-speed sequences, this has consequences not only in the camera but also later in the workflow.
More frames mean more files.
Higher resolution means larger files.
Higher burst rates mean more files are generated in less time.
The performance advantage therefore continues beyond the camera and into the computer, SSD, catalogue and image-processing software.
What does this mean for Birds in Flight photography?
This is where the technical comparison becomes practical.
For a static landscape, portrait or architectural photograph, the difference between 20 fps and 40 fps may have very little practical significance.
Birds in Flight are different.
A bird does not simply move from Point A to Point B. Its wings, head, body and tail can change position dramatically between successive frames.
At 20 fps, the photographer already has a very high sampling rate.
At 40 fps, the camera can sample the action at approximately half the temporal interval.
That can increase the probability of capturing a particularly desirable wing position, head angle, eye position or interaction with another bird.
But the real advantage is not simply the number 40.
It is the combination of:
high frame rate + high-resolution sensor + fast sensor readout + AF tracking + processing + buffer capacity + high-speed storage.
That is the data-throughput advantage.
The modern camera as an imaging pipeline
The EOS R6 and EOS R6 Mark III therefore illustrate two stages in the evolution of mirrorless camera technology.
The R6 was already an extremely capable high-speed full-frame camera. Its 20 fps electronic shooting and substantial RAW/C-RAW buffering made it highly effective for action photography.
The R6 Mark III takes that concept considerably further.
It combines a 32.5-megapixel sensor with up to 40 fps electronic continuous shooting, a CFexpress Type B storage pathway and a substantially greater ability to manage high-volume image data.
The result is not simply a camera that “shoots twice as fast.”
It is a camera designed around a considerably higher data-throughput requirement.
That distinction matters.
The progression of digital cameras is increasingly becoming a progression from image capture to real-time information processing.
From shutter speed to data speed
For many years, photographic discussions centred on shutter speed.
Then came autofocus speed.
Then frame rate.
Today, these specifications are increasingly interconnected.
A modern mirrorless camera has to capture enormous quantities of sensor information, analyse the scene, track subjects, calculate exposure, maintain autofocus, construct image files, manage an internal buffer and transfer those files to increasingly sophisticated storage media.
The photographer experiences all of this as something deceptively simple:
press the shutter and keep shooting.
Behind that action, however, is an increasingly complex computational pipeline.
The comparison between the EOS R6 and EOS R6 Mark III demonstrates why the headline FPS figure is only one measurement of camera performance.
The more useful question is:
How much photographic information can the camera capture, process, temporarily store and ultimately write without disrupting the photographer's sequence?
That is the question of data throughput.
And as mirrorless cameras continue to evolve, it may become a more useful way of understanding photographic performance than frames per second alone.
