Don’t Use SD Cards with Your Canon 5D Mark III If You Care About Speed

Photographer Jeff Cable purchased a couple Canon 5D Mark IIIs recently and discovered that although the camera offers both SD and CF card slots, you should avoid the SD slot if you want maximum shooting speed. He writes,

[…] 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 […] Without UHS [Ultra High Speed] 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

It turns out that the camera will default to the slowest 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.

It might not be a big deal for most photographers, but if your line of work requires clearing the camera’s buffer as quickly as possible, it something you might want to be aware of.

Why you should not put an SD card in your Canon 5D Mark III (via Photography Bay)

Image credit: Photograph by Jeff Cable

  • Jens Hamada

    has he tested with the latest firmware?

  • Mansgame

    What’s a 133x?  I thought SD cards were different classes and then how many MB/Sec they were…

  • Osmosisstudios

    Does the 5DIII ever make a CLAIM that it supports UHS? Nope.  It’s called READING folks; you should probably do it before dropping $3k on something.

  • perceptionalreality

    There are several different notations for the speed of the cards. The wikipedia article on SD cards explains it well. 

  • Eviljedi71

    @a4fb39cdd1429da4fdde97551ba9248d:disqus Great point. Always do you research before buying and using any equipment.

  • Hawk1500

    The problem isn’t Canon claiming it or not, but the fact that most people probably don’t know that just by having a SD card inserted, your CF write speeds are crippled as well.

  • Guest

    Agree. This article is not about bashing Canon, it just tell what the camera  can and can’t, does and does not, do. Make it part of your research.

  • John Kantor

    Don’t try to justify another dipshit move by Canon. His mistake is not buying Nikon.

  • John Kantor

    Another dipshit move by Canon. His mistake is not buying Nikon.

  • AMT

    I’ll have to test this tonight.

    Anyway, can be easily solved by firmware update. The problem is whether Canon will include this in their firmware update or not, and when?

  • hawk1500

    perhaps the way the camera defaults to the lowest speed, but not the slow SD write speeds. Although, who knows, maybe it’s more complicated because the camera may not be able to write at two different speeds to each of the card or some other reason and Canon just figured it’s easier to make it slow for both slots.

  • Overnight_guest

     Are the childish remarks really necessary?    The whole Canon/Nikon thing is just exactly that, childish….which pretty much sums up your comment as well.

    They are both excellent cameras, if you can’t get outstanding results with either brand, then the problem is not the camera but the large carbon-based unit behind it. 

    So, lets try playing nice, ok?

  • SB Photo

    John Kantor, you’ve clearly made your point. Now please move on unless you’ve actually got something constructive to add.

  • Eziz

    Logically it makes sense. Since same processing power is used to clear out buffers the slowest speed will be used as default. 

  • John Stock

    Grow up.

  • Taras

    If you read user guide, chapter about SD, you should be abel to see notification about low level formating and performence of SD card.

  • GTK

    I guess all cameras with dual memory slots slow down to the speed of the slowest card, no?

    Does the same happen in the D300s with it’s CF and SD slots?

  • David

    Is it just me that sees this as pretty obvious?

    SD cards are not as fast as CF, which is well known and why we have UMDA slots on cameras such as the 5d3, and don’t just use SD as standard.

    If you are writing to two card simultaneously, it is then common sense that the camera will work at the slowest cards speed, otherwise when writing images to card the CF buffer will clear quickly, and leave you with a backlog of images waiting to be written to SD – at some point this fills the buffer and you won’t be able to write to either, hence the camera defaults to the slowest standard so it can maintain constant performance.

    The fact that Canon didn’t include a high speed standard for the SD may be a bit of an oversight, but never really a hidden fact – if shooting professionally, would you not want to look up the SD specs to find out the fastest option before just jamming in any old SD card?

  • Dirrty Sanchez

    When I shoot weddings I like to shot raw+jpeg for many reasons. That way I can delete the vast number of raw shots in post if the jpeg looks fine, and keep the odd raw for the premier shots and any I need to recover shadows / highlights. You definitely don’t want to keep keep terabytes of shots for decades when gigs will suffice.

    I was hoping to use CF for RAW and SD for JPEG. Could save my bacon if one card goes faulty. I’m now wishing they had two XQD cards instead.

  • Giulio Sciorio

    Any no Eye-Fi support either.

  • Andrew Davis

    ? The 5D3 supports my EyeFi card very nicely, much better than using it in a CF adapter in my Mark2.

  • Giulio Sciorio

    Thats great news Andrew. A good friend of mine has a MKIII and can’t figure it out. Got a link to directions I can pass on to him?

  • Happy_Tinfoil_Cat

    Thanks for the info, it’s helpful. It’s not as obvious as people seem to think. As an engineer, I see no reason the CF and SD can’t work at full speed. Even if they didn’t implement the latest SD interface you should still be able to configure the CF to write the raw files and the SD the JPEGs. The JPEGs are a fraction of the size of the raw files and would take about the same amount of time to write. Hopefully Canon put the hardware in the camera and just needs to finish the firmware to use it fully.

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  • Photography

    Jeff Cable is really brilliant photographer. I also see no reason the CF and SD can not work at full speed. These all information really very informative to me.

  • Chuck Kuhn

    CF for Raw and SD for Jpeg, is what I use.

  • Gene

    If you program the camera to first load the faster CF card then fill the SD card why would the camera default to the slower card?

  • John

    Hi Guys,

    Don’t know really how this affects the write speed in video mode but I’ve been shooting with my 5DMIII on a SD UHS1 and I always get about 80-90Mbps in ALL-I mode. Does anyone know the application/effect in video mode?

    thanks in advanced!

  • David Portass

    No, Nikon fortunately made the SD slots use the fasted tech at the time, for example the D600 has 2 slots that use UHS-I SDHX/SDXC, The D800 supports UDMA 7 CF and UHS-I SDHX/SDXC. It doesn’t make sense why Canon would do this.

    For most shooters this won’t be an issue at all. It’s just my personal preference for my own piece of mind if shooting for a client to shoot with 2 cards in backup mode because while rare, I’ve known some togs who have lost images or had to send off the card for professional repair, one recent one was on a 1D2 for a charity event so was minimal pay had to fork out nearly £200 recovery fee because the card was damaged so they had to remove the chip from the card itself into a doner card to get most of the photos back)