Canon 5D Mark IV doesn’t run at full speed

Yesterday the latest Canon DSLR hit the streets: the EOS 5D Mark IV.

One of the selling points of this camera for action photographers is that it can run at 7 frames per second (7 fps). However in my testing this seems to be a hollow claim!

The only way I have been able to achieve 7 fps with the 5D Mark IV is to either set the lens to manual focus or to select One Shot AF. Whenever AI Servo is selected (which should expected for anyone photographing sports or wildlife like myself) the camera drops back to 6 fps. These are only preliminary results at this stage, but it’s surprising enough to warrant mention at this stage.

UPDATE: To maintain 7 fps all you need to do is make sure your battery doesn’t drop below 50% charge. This is explored further in the next article on the blog.

My testing

Whenever I get a new “action camera” and/or a new model of memory card I measure how fast the camera can write to it. The manufacturer-supplied numbers are always misleading, and testing in the particular device is required. By knowing how each card performs I can use the best cards for each camera and maximise the performance. I don’t usually shoot long bursts of photos, but when I need to I’d like to be sure that the camera’s not going to pause because I’m not using the right card.

I like to think my testing is reasonably scientific, and it involves recording the camera shooting a long burst of frames using another video camera. Analysis of the audio track provides precise timing of the frame rate. Using a standard scene and illumination and shooting in RAW, the tests provide results such as:

  • MB/s written,
  • card frame rate (how many frames can be written per second on average, either when the buffer is full or in terms of how fast the buffer empties),
  • burst frame rate (supposedly 7 in high-speed continuous with this camera),
  • number of frames in a burst before the buffer fills and the camera slows down (supposedly 21 with a UDMA7 card),
  • length of that burst in seconds (easily calculated from the above numbers: 21/7 should mean 3 seconds).

I soon noticed that the 5D Mark IV was shooting at 6.0 fps, not 7!

Not the first time Canon has done something like this

L1_029302Now this isn’t completely unexpected. The earlier EOS 5D Mark III was advertised as achieving 6 fps, and it did: some of the time. I found that when the 5D’s AI Servo 2nd image priority was set to “Focus” (making the camera pause in a burst if you had AF engaged and the subject had moved out of focus) that the camera slowed down to 4 fps.

Do note that I use back-button focus, and the camera only tries to focus while the AF-ON button is depressed. In my tests the camera wasn’t trying to keep focussed locked on a subject: the AF-ON button was not pressed. But the camera refused to fire faster than 4 frames per second even when AF wasn’t engaged! Switching the lens to manual focus or changing the focus priority setting back to the default let the camera suddenly jump up to 6 fps.

The EOS 1Dx did not suffer from this slow down. Nor did the later 7D Mark II or 5Ds R. As a result the 5Ds R was a speed increase for me (5 fps vs the 5D Mark III’s 4 fps).

What causes the slow down?

The AI Servo image priority settings were my first suspects, but even after changing all the AF settings back to factory defaults the 5D Mark IV has stayed at 6 fps. Maybe there is still a particular setting I’ll find in the coming days which resolves the problem, but so far the only ways I’ve managed to get the camera to shoot at 7 fps have been to either:

  • set the lens to manual focus, or
  • select One Shot AF (where the camera stops focussing before shooting the burst).

Neither of these configurations are useful for shooting sports or wildlife! The photographers most attracted to the 7 fps shooting are not going to be able to use it.
I say again: these are only preliminary findings. Research is ongoing (and I expect to publish card speed results for my cards in the 5Ds R and 5D Mark IV soon).

The silver lining

6 fps is still a reasonable burst speed, and you do get a benefit from using it.

The 5D Mark IV’s card interfaces have sped up from the 5Ds R and earlier cameras, and as an example in my testing so far the SanDisk Extreme Pro “160 MB/s” 32 GB CompactFlash has jumped from under 90 MB/s to around 110 MB/s [preliminary numbers!]. On the test scene I was shooting today, at 7 fps (manual focus) the 5D Mark IV achieved a buffer of 28 frames (and an underlying card frame rate of around 3.5 fps). This equates to a buffer length of 4 seconds (compared to Canon’s 3 seconds). This isn’t unexpected: fast cards like this SanDisk and the Lexar 1066x cards have historically surpassed the performance numbers provided by Canon for other camera models.

But when the frame rate slows down to 6 fps by engaging AI Servo, the buffer expands to around 34 frames which equates to 5.7 seconds! This is a significant upgrade from other 5D cameras! In the 5Ds R at 5 fps the longest I’ve achieved is 18 frames (3.6 seconds).

If we can’t find a way to get the 5D Mark IV to 7 fps in AI Servo, maybe we’ll have to settle for this benefit of the new camera.

UPDATE: [2016-09-10] As mentioned above I have now achieved 7 fps. See the next article on the blog for clarification.

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