UPDATE – It should be noted that Jeff has clarified his post (simply having the card there doesn't impact write speed):
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.
I haven't tried this but thought it was significant enough that it should be reported!
Jeff Cables reports:
I am going to start this by saying that I really like my Canon 5D Mark III cameras and use them for shooting everything including Bar and Bat Mitzvahs, landscapes, portraits, sports and more. But just after receiving my two cameras I started to play with the memory slots and experimented with the best way to use both memory card slots. My first thought was…it would be great to shoot RAW images to both cards as a backup measure, and my second thought was…I could shoot RAW to the CompactFlash card and JPG to the SD card.Well…after some testing I have determined that, if you care at all about high speed shooting or clearing you buffer quickly, YOU DO NOT want to put a card in the SD slot. Why? Because, for some reason unbeknownst to me, Canon decided to build the 5D Mark III with one very fast CF slot which supports the newer UDMA7 protocol and a standard SD card slot which does NOT support the high speed standard called UHS – for Ultra High Speed. This is really strange because many other cameras have come out with UHS1 compatible slots over the last year. Without UHS support, the top speed that can be achieved by the SD card is 133x. This is true even if you purchase a 600x SD card and insert it in the camera. The best you will get is 133x …
Read Jeff's entire report! Jeff Cables Blog: Why you should not put an SD card in your Canon 5D Mark III if you care about speed.
What do you think?
Have you noticed anything like this?
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