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Old Jan 21, 2010, 2:09 PM   #1
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Default Confused about SD memory cards

I know there's no shortage of talk here about the appropriate memory card for my Canon T1i, but I'm still a bit confused.

I was pricing them online today at found a wide variety on the Future Shop website. But check this out:

  1. CoreMicro 8GB SDHC Class 6 High-Speed Memory Card - $29.99
  2. SanDisk Extreme III 8GB SDHC Class 6 Memory Card - $119.99

WTF? Could there really be that much difference between the CoreMicro and the SanDisk?

Then there's a Panasonic 8GB SD Class 10 Memory Card for $69.99. (No mention of "HC" though.)

In theory I'd like to be able to record the highest quality HD video at 1080p that my camera allows. Right now I'm using a cheapo 8GB SDHC card... I think it only cost me a ballpark $30.

Also, can someone explain this buffer stuff to me? Thanks in advance.

Last edited by Boldstar; Jan 21, 2010 at 2:12 PM.
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Old Jan 21, 2010, 2:42 PM   #2
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Unless you're seeing errors or early termination of video recording because your existing card can't keep up with the speed the camera needs to write to it, a faster card isn't going to help (and won't impact the quality of your video).

You will sometimes see problems with cards that are too slow to keep up with how fast the camera is able to write to them, reducing the amount of time you can record video without an error or delay. Ditto for how fast the camera's buffer (fast internal memory) takes to complete writing to the card after you finish shooting. A slower card may also mean you won't be able to take as many photos before the camera slows down (and it's "full buffer" frame rate may be slower).

But, you won't see any difference in image quality or video quality with a slower card. The speed of the card doesn't have anything to do with image or video quality (unless you have a defective card).

As for price differences, just like any other product, you have a wide variety of factors involved with pricing, including perceived quality, brand name recognition, reliability, and more. For example, I've never heard of CoreMicro before.

In addition to the class ratings you see with SDHC now (for example, a Class 6 card means it should support a minimum continuous write speed of 6MB/Second, which is plenty fast for the speed your camera uses for video recording), you also have card manufacturer's rated speeds (which are sometimes a bit on the optimistic side).

For the newer Sandisk Extreme III Cards, that's 30MB/Second (for those that are marked that way, as some of the older cards were slower). Note that the Class 10 rating (minimum sustained write speed of 10MB/Second) is relatively new. So many cards that would meet that rating are still marked as Class 6 (because the Class 10 rating didn't exist when they were manufactured). But, also note that you'll tend to get diminishing returns with faster cards. For example, you may buy a card that's twice as fast and see little to no difference in performance once you get to a certain card speed (because the camera usually becomes the bottleneck at some point, not the speed of the card).
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Old Jan 21, 2010, 2:51 PM   #3
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Here are some test results for various cards in an EOS-450D. Rob hasn't updated them in a while and the EOS-500D wasn't tested. But, you should be able to get an idea of how some of the cards are going to stack up against each other with it.

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Old Jan 21, 2010, 3:20 PM   #4
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I have a t1i and I have tested sandisk Class 4 8gb Ultra II with a 12min hd at 1080, had no issues. Having a backup card is a good idea. I have the panasonic 8gb gold class 6 and it works as well as my delkin 16gb class 6 card.

The only time I notice any difference between the Ultra II and the panasonic or delkin is on long burst rates shooting in jpeg/raw in the highest resolution. Then it does slow down a bit after like 3 seconds of burst.
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Last edited by shoturtle; Jan 21, 2010 at 3:22 PM.
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Old Jan 21, 2010, 3:57 PM   #5
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I'm not sure if anyone has explained "buffer" to you, as of yet.

If you think of buffer in this way, it'll make sense.

Your camera can CAPTURE a ton of information (e.g. photograph you just shot) really, really fast.
Your camera can WRITE that information on your card fast, but not really, really fast. The writing mechanism is slower than the capturing mechanism.

To bridge that problem, you could:

A. Not allow the camera to take the next photo until it had finished writing everything. (That would stink)

B. Find a temporary home for that information that could record information just about as fast as the camera can, hold it until the writing mechanism of the camera catches up.

Thank goodness they chose option B. And option B is called the buffer.

It's like short term home for information waiting to be written on the card.


Last edited by FaithfulPastor; Jan 21, 2010 at 4:06 PM.
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Old Jan 28, 2010, 10:33 AM   #6
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Thanks for the help guys. I think I have a better idea about how things work now.
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