Update – Why You Should Better Not Use An SD Card With The EOS 5D Mark III

Better Not Use An SD Card With The EOS 5D Mark III

Update: Reader AI pointed out that the post was incomplete. Thanks AI. You can read it in the comment section. I post his comment here:

Jeff Cable said…
As many of you have pointed out, the degradation in speed will occur when you are attempting to use both the CF and the SD to write files. If you have an SD card in the camera and are not writing to it, you will be fine. I am not sure why you would want that (except for overflow), but this is the case.

Someone also brought up the speed difference in writing RAW+JPEG vs RAW+RAW. This is also true on the 1Dx. I believe that this is due to the fact that the camera has to process the file twice (once for RAW and once for JPEG) which takes longer than clearing two RAW files from the buffer. I was hoping to shoot RAW+JPEG at the Olympics with the 1Dx but will now shoot RAW+RAW only.
June 25, 2012 6:12 PM

So, the slow down issue only affects someone if your writing images to both cards, at the same time. You will get normal, native speeds on either card if your only writing to one or the other….

While having both a CF and an SD card slot is certainly a good feature, unfortunately it appears that there is an issue with the Canon EOS 5D Mark III (price & specs).

Photographer Jeff Cable found out that using an SD card slows down buffer and write speed of the EOS 5D Mark III. While the 5D Mark III supports the UDMA7 CompactFlash protocol (speed up to 90MB/sec) it seems it does not support the UHS-1 (ultra high speed) standard for SD cards. What does that mean? It means that whatever SD card you will use, the 5D Mark III will always write 20MB/sec instead of 45MB/sec (which conforms to the UHS-1 specs). And that’s not all of the bad news: if you pull both a CF and an SD card in your 5D Mark III, the cam will switch to the slowest speed for both cards. In other words: your pricey UDMA7 CF card will perform at lame 20MB/sec.

The solution: use only the CF card. The solution #2: Canon please fix this with a firmware update!

[BorrowLenses.com via slrlounge]
  • Al

    Not sure why this old story is being dredged up but your post doesn’t include the update from Jeff who wrote the original article…

    Jeff Cable said…
    As many of you have pointed out, the degradation in speed will occur when you are attempting to use both the CF and the SD to write files. If you have an SD card in the camera and are not writing to it, you will be fine. I am not sure why you would want that (except for overflow), but this is the case.

    Someone also brought up the speed difference in writing RAW+JPEG vs RAW+RAW. This is also true on the 1Dx. I believe that this is due to the fact that the camera has to process the file twice (once for RAW and once for JPEG) which takes longer than clearing two RAW files from the buffer. I was hoping to shoot RAW+JPEG at the Olympics with the 1Dx but will now shoot RAW+RAW only.
    June 25, 2012 6:12 PM

    So, the slow down issue only affects someone if your writing images to both cards, at the same time. You will get normal, native speeds on either card if your only writing to one or the other….

    • Admin

      thanks AI, missed that

  • Bob B.

    I think the wording in the above post is misleading. If I put two cards in my 5DIII….The only time that the camera writes at 20MB/sec to the CF card is when I have the camera set to record to both cards (CF & SD) at once for an image. (i.e. I take a photo, the photo is recorded on the CF card AND the SD card at the same time). If I I set the camera to record to the CF card ONLY, even though I still have an SD card in the card slot, my camera will write to a 600X CF card at the higher speed (example 45MB/ sec). I do NOT have to take the SD card out of the camera to have the higher speed writing on the CFCard, ONLY. This is my experience…but I am certainly open to discussion on this point.
    Can anyone else please post their personal experience regarding this matter…I would like to confirm my own experience with other 5D III users.
    Thanks.

  • Bob B.

    There is a long lag from when I write a post to this site to when it actually appears here. My first comment I wrote before Al posted. Al…thanks for confirming my personal experience regarding the writing to the CF card…but I have to point out an in consistency with my personal experience and what you stated regarding the SD card in a 5D III.
    You wrote: “So, the slow down issue only affects someone if your writing images to both cards, at the same time. You will get normal, native speeds on either card if your only writing to one or the other….”.
    I do NOT get normal native speeds on both cards if I write ONLY to the SD card. The SD card is ALWAYS 20 MB/ second, regardless if I write to it alone OR when writing to it ad the CF card simultaneously.
    If I put 45MB/sec CF AND SD cards in my camera, and then put my shooting speed on High Frame Rate,( and first shoot to the CF card only and then shoot to the SD card only), the continuous burst onto the CF card is ALWAYS 4or 5 frames more to the CF card before the camera starts to buffer. The SD card does not record at its native rate even when I have the camera set to record to the SD card ONLY.
    I think you will find this to be true, too.

  • Frank B

    OK I am not sure the CF slows to the speed of the SD card slot. I shoot full RAW to the CF and medium quality JPEG to the SD card. Yes my burst defaults to 7 but with the smaller JPEG I hit seven and it takes a second to clear the buffer. If the CF was really running at only 22MB/s it would take allot longer for the CF to finish writing the large RAW files.