Using an SD and CF Card Simultaneously in your 5D MKIII Might Be a Bad Idea

Recently, Jeff Cable from Lexar published a blog post explaining a rather curious choice on Canon’s part. It seems that the 5D Mark III was built 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). Without UHS support, the top speed that can be achieved by the SD card is 133x. Because the 5D MKIII defaults to the slowest memory card speed inserted in the camera, your CF speed could get short-changed by the SD card.

Jeff explains that he first discovered this problem when he decided to do something that makes perfect sense to a photographer: shoot RAW to one card and JPEG to another, or just shoot RAW to both to act as a backup. But because of the way they designed the SD card slot to work, 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.

What is most painful, but makes sense based on the decision by Canon to not give the SD slot UHS support, is that the 5D MKIII will shoot only as fast as the fasted card inserted. “So, if you have a 1000x CF card in slot one and any SD card in the second slot, the very best buffer clear that will achieve is 133x. When shooting sports or any type of images with burst mode (6 frames per second), this is crippling… Why would I want to clear data at 20MB per second when I could be transferring at 90MB per second or better?”

An excellent question Jeff. What do you all think? Does this problem bother you? Would you have even noticed if Jeff didn’t say anything? Let us know in the comments below.

[Via Jeff Cable's Blog]
Photo copyright Jeff Cable