CFexpress Type B vs SD cards: what speed do you need?
Understand card write speeds, V30, V60 and V90 ratings, and which CFexpress Type B or SD cards suit your camera's photo and video settings.
The short version: Buy the card format your camera accepts, then match its sustained write performance to the recording mode you need. SD is enough for many photographs and video modes, while demanding modes can require CFexpress Type B. Capacity and advertised peak read speed do not tell you whether a card will record reliably.
Start with the camera’s card slots
CFexpress Type B and SD are different formats. You cannot put either into the other’s slot, so check the camera manual before comparing speeds.
The Canon EOS R5 Mark II has one CFexpress Type B slot and one SD slot supporting UHS-II. Its compatible-card guidance also confirms support for UHS-I SD cards.
Two slots do not mean every recording mode works on both. The format the camera accepts and the performance a particular setting requires are separate checks.
If you use a card reader, check that it supports the exact format too.
Read speed and write speed do different jobs
Read speed matters when copying photographs or footage from the card. Write speed matters when the camera is saving them.
The large number on a package may describe a maximum read speed achieved under particular conditions. It does not establish how quickly the card can keep accepting data during a long recording.
Look for sustained write information, relevant certification and the camera manufacturer’s requirements. For the R5 Mark II, Canon points to VPG400 CFexpress cards or cards with ample performance for the chosen movie quality.
A 512GB card describes storage capacity. It says nothing by itself about sustained performance. If checking a ProGrade 512GB card, identify its full model and rating before matching it to a recording mode.
What V30, V60 and V90 mean
These are SD Video Speed Class ratings for minimum sustained sequential write performance under the standard’s defined conditions, as Kingston’s guide confirms:
- V30: 30MB/s.
- V60: 60MB/s.
- V90: 90MB/s.
The SD Association explains the speed classes and the need for a compatible host and bus mode. Its FAQ also covers how to match cards and devices.
UHS-I and UHS-II describe interface standards, not those minimum write guarantees. A UHS-II label alone does not make a card V90.
Follow the class the camera specifies. Do not choose solely from a package saying it is suitable for 4K or 8K.
Convert video bit rate carefully
Camera bit rates are commonly shown in megabits per second, written Mb/s or Mbps. Card speeds use megabytes per second, written MB/s.
There are eight bits in a byte. A video stream of 400Mb/s is therefore 50MB/s before allowing for other recorded data and overhead.
That calculation helps explain the scale, but it is not a card approval test. Audio, metadata, multiple streams and the camera’s recording method can affect requirements.
Use the manual’s card table rather than choosing a rating that only just exceeds your calculation.
What the R5 Mark II needs for specific modes
Canon’s recording specifications show why resolution alone is insufficient:
- 4K Normal, 25p, XF-HEVC S YCC422 10-bit, Standard LGOP: SD U3 is listed.
- 4K Normal, 50p, in that same format and compression: SD V60 is listed.
- 8K Standard RAW, 25p: CFexpress Type B at 400MB/s or faster is listed; SD is unavailable.
Those requirements apply to those exact combinations. Changing compression, frame rate or recording quality can change the card requirement.
For still photographs, burst behaviour also depends on file format, shooting settings and card performance. A camera can temporarily hold frames in its buffer, then slow as it waits to write them.
Try this before an important shoot
Write down your intended resolution, frame rate, compression and recording format. Find that exact combination in the camera’s current manual and match its card requirement.
Back up anything already on the card, then format it in the camera. Canon recommends in-camera formatting for a new card or one previously formatted elsewhere.
Record several minutes using the intended settings. Check for warnings or recording stops, then copy the files and play them back.
For photographs, test the burst length you actually need and how long the camera takes to become ready again. Repeat if you change card model or recording settings. Choose the card that meets those needs with dependable performance.
Sources and further reading
Spotted something wrong or out of date? Email hello@shuttersnack.com and we'll fix it.