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Gear Talk => EOS Bodies - For Stills => Topic started by: infared on January 04, 2013, 08:19:43 AM

Title: Canon 5DIII and Media Cards...
Post by: infared on January 04, 2013, 08:19:43 AM
I know that this is an old discussion topic...but I just am trying to clarify things for my (old) brain.
Regarding how the 5DIII records to to the two different card types, my readings and my own findings with my
camera tell me that:
1. If I write to the CF Card ONLY  the write speed will be native to that card (with or without an SD card in the camera). i.e. a 600X card will record at or about 45MB/sec.
2. If I write to the SD Card ONLY the camera can only write up to 20MB/sec regardless as to the write-speed of the SD card that I put in the card slot. i.e. If I put a 600x SD card in the slot with 45MB/sec rated speed, the Camera will only be able to write to that card at 20MB/sec.
3. If I have a CF card and an SD card in each slot, both rated at 45MB/sec and set the camera to write to both cards simultaneously, in the same image type to each card (i.e. RAW, Jpeg, etc.),  when I record an image, both cards will be written to at the slower, 20MB sec rate.
4. If I set the camera to write to both cards with different imaged types (i.e. write RAW to the CF and Jpeg to the SD, or visca-versa the writing will take a longer time than if the camera was set to write the same type of image to each card as in #3 above.
What is the fastest CF card that the camera can write to at the cards native write speed? i.e. how fast can the camera write to a CF card?
Any input to confirm 1-4 above or to increase my understanding of my camera would be welcome...I think I have it correct..but I could be wrong.
Title: Re: Canon 5DIII and Media Cards...
Post by: msatter on January 04, 2013, 03:02:45 PM
The answers can be found here on the discontinued website of the great Rob Galbraith: (

Title: Re: Canon 5DIII and Media Cards...
Post by: Mt Spokane Photography on January 04, 2013, 03:33:22 PM
SDHC Cards seldom write at more than 10 MB/sec once they have been used.  The figures on Roger Gailbrathe's page only apply to a newly erased card, and that is not the same as a formatted card, its a low level format that can take 30 minutes or more.  The 5D MK III can do a low level format on a SD card, but its a battery eater.
On the other hand, CF cards will write much faster, even if they have been used and filled with data.
Since the slowest card to write is going to limit you when writing to both cards, except for the unusual case of totally blank cards, 10 MB/sec is the most common limit.