I have a Canon 20D and was looking to buy a memory card. Turns out there are lots of options that vary in price. This got me wondering, what should I be looking out for when buying a memory card.

Based on some research that I've done, I have some points:

  1. What is the maximum memory size your camera supports ?

    • From what I can tell, the 20D supports up to 8GB (could not find it in the manual), so anything over that would be a waste. Although I did find some posts where users claim they can use a larger card, as long as they dont format it using the camera. Can anyone speak to that? Personally I might just stick with the limit set by the camera.
  2. Read/Write Speed?

    • I am still trying to figure this one out. I saw this post on speeds that sheds some light. Essentially the write speed of the card should be higher than that of the camera, which makes sense. However how do I figure out the write speed of my camera? Does anyone know what the write speed of a Canon 20d is?
  3. What brand to buy?

    • I currently have a SanDisk Extreme 512MB card. That is why I started looking for the same card with a higher capacity. A Kingston or Transcend is approx. $15 while a SanDisk is over $30...
  4. Extreme temperatures?

    • Not sure how important this is, but I do live where the temperature can go pretty low below 0F. That doesn't mean I will necessarily be doing photography outside in that temperature. What kind of problems do people run in to with low temp?

Are there any other things that I should be looking at?

  • 4
    The current state of cards and readers is MUCH faster than the maximum write capability of the 20D. I don't think he wants a 600X or 1000X card just for faster downloads if the camera can only write at 133-150X speeds. A SanDisk Extreme 8GB only runs about $30 at amazon.com and can handle write speeds 10x faster than the 20D.
    – Michael C
    Nov 16, 2013 at 21:24
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    well, for me it was emptying the card onto my computer that was annoying until I got the sandisk extreme set. we're talking 1Mb/s vs 30Mb/s. Also I never had a card go bad on me after switching over to those. Nov 16, 2013 at 21:39
  • 1
    The SanDisk Extreme 8GB is rated at 30MB/sec. The 16GB card you recommended won't even format in the 20D. Formatting in-camera is always the recommended way to erase the card.
    – Michael C
    Nov 16, 2013 at 21:58
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    There are a substantial amount of 'fake' branded memory cards around and it is often not possible to distinguish fake from real by appearances. I used to always use Transcend CF cards due to superb results and reliability. Some years ago I experienced a sudden change in reliability with all Transcend cards I bought having problems. I currently mainly use SD and have standardised on SANDISK with, so far, good results. Whether my Transcend experiences are due to fake cards being sold in the local retail markets I cannot tell. Nov 21, 2013 at 21:11
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    In-camera formating is recommended by all card makers. If you reformat cards in another system (PC or other) you need to be sure that the directory structure is written correctly for the system used. While in many cases the default value may be correct, some systems use unusual arrangements and out of camera reformatting may cause problems. (eg an older A series Canon that I am using for CHDK time lapse ). Nov 21, 2013 at 21:13

4 Answers 4


The Canon 20D topped out at around 6 MB/sec when Rob Galbraith tested many of the cards currently available back in 2006 or so. Considering that the 30D improved to almost 7 MB/sec using many of the same cards, I would say anything over 6 MB/sec is overkill for the 20D. The slowest cards on the market today are faster than that, unless they are unsold older stock.

As far as reliability goes, I've never had a problem with any card from SanDisK, Transcend, or Lexar. My newer cards are all the Transcend brand. I've used them heavily for years. I follow a couple of simple rules: NEVER insert or remove a CF card in a device that is powered on. SD cards and USB drives are designed to be hot swappable if "ejected" properly before removal. The design standards for CF includes no such provision. Also, rather than "erasing all images" from a card, I format the card in the camera in which it will be used.

The design standard for all CF cards is a lot more tolerant of extreme temperatures than other types of flash memory such as SD cards. SanDisk touts the durability of their cards when used in extreme temperatures and at high altitudes. My own experience shooting in sub-freezing weather is that it is a non-issue with any of the cards I own.

In cold environments battery life will be your primary concern. Take at least two and keep one warm with the body heat inside your clothes while you shoot with the other. You can swap them and warm the cold one back up and it will 'recover' some of the energy it lost as it was cooled.


You seem to have done your research well. Considerations are reliability, speed and size:

  • Reliability is the hardest to quantify and, while all brands eventually have failures, the most reputable brands tend to be the most reliable. Lexar, Kingston and Sandisk are most reliable. Note that even among these, they are levels of cards Sandisk red and black cards are the most reliable, while blue ones are only average. Stay away from most other brands. I would be very wary about a brand like Scandisk who is probably fishing on people confusing it with Sandisk.

  • Speed has two sides: read and write. Most manufacturer's quote only the read speed which matters when you are downloading from a sufficiently fast reader but not in-camera. Since your 20D is old, I would say that 150X is already around its limit. You can buy 1000X cards now!

  • Size of CF cards is not really a problem. That is one beauty of the standard. While SD cards had to be updated to SDHC after 2 GB and to SDXC at 64 BG. Compact Flash cards are workable as long as the camera can recognize the file-system. Still, most people avoid really big cards unless shooting video - which the 20D cannot - because that puts too many eggs in one basket. As I said, even the best cards can fail from manufacturing defects or from corruption.

Living in Canada for several decades, I can tell you that I have never seen any card or any type or brand suffer in the cold. Other than Microdrives, I have also never seen any card fail because of altitude. I was a guide in Ecuador and Peru, spending over a year in at 10,000' (3000m) of altitude. I shoot in the cold for month each year and have seen many cameras fail but never a single card.

  • from ur experience of "many cameras fail", have u seen any budget DSLR camera that is quite cold/altitude tolerant for its price range?
    – kmonsoor
    Nov 19, 2013 at 20:10
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    The most weatherproof DSLRs are from Pentax. The entry-level K-30 and K-50 are very well priced and unmatched for their feature-set. They are the only ones rated to work down to -10C (14F). Altitude itself is not a problem with DSLRs, only cold, mostly because of the battery. I usually keep an extra battery inside my glove to keep it warm and within easy reach.
    – Itai
    Nov 20, 2013 at 3:19
  • "The most weatherproof DSLRs are from Pentax." This might be a little clearer if it included the words entry or mid level. As in, "The most weatherproof entry or mid level DSLRs are from Pentax." I'm fairly confident that the K-50 might be close to or just as weatherproof as a D4 or 1D X, but I highly doubt they are more weatherproof than those and other top tier pro bodies.
    – Michael C
    Nov 20, 2013 at 8:53
  • Note that the D4 or the 1D X are not even rated to operate below freezing. I've had a D4 but a not a 1D X. It indeed felt even more solid and just as weatherproof but that was just a feeling. All these cameras stood rain, snow and below freezing temperatures but not exactly the same conditions.
    – Itai
    Nov 20, 2013 at 13:48
  • (Cont'd) However, I have rinsed several Pentax DSLRs straight under the running faucet to get sand out of them, which used to happen a lot because I lead an annual photo tour through the desert in Peru. The Nikon user manual even explicitly says not to do that! Partly this may be to protect themselves but it says who is more confident about their weatherproofing.
    – Itai
    Nov 20, 2013 at 13:51

The speed of the card is not a concern while it is in the camera. But if you , like I always did, transfer to PC through a card reader, you will see a huge difference, but only if you use the rather expensive branded cardreaders, not those 10$ readers at the checkouts at supermarkets and hardware stores.

There are only two brands/models to consider (in my area at least) if you want a robust and fast card. Sandisk Extreme (Pro) and Lexar Professional. Supposedly, they are same quality, but I've done a lot of shooting in orchards in a california valley in the middle of the night (stayed there from 4PM through 4 AM) every night, every day in the week for a month at a time. It was very cold and VERY humid. Had to wipe off the lenses every 5 minutes. One out of three Lexar Professional died on me, while Sandisk Extreme (III at the time) worked great and still works 4 years later. So I stick to Sandisk Extreme, even though it is not scientifically enough empirical evidence.

The Extreme in the name is exactly that; for extreme conditions and temperatures. You really have to try with intention to break it. -25 C to 85C operating. And vibration resistance. Storage temperature down to -45C I believe.

Since you already have this brand, and have no issues with it, it is better to stick with it. Don't fix what "aint" broken as we say (engineers).

Regarding size: Your camera have full support for 8Gb, but can use 16Gb if you manage it (like I always did) on your computer (format and delete files). You can probably get 2x8Gb for the same price, if you need 16Gb and have a camera bag with CF slots.


well, so many good advices. I add one: 4Gx4 is better than 8Gx2, also even better than 16Gx1 storage card may be damaged...so you should know the reason why I add this one

  • It depends on how fast you fill those cards up and how fast the action is that you are trying to capture. When shooting a high paced sporting event where the action doesn't stop for long intervals, the last thing you want to happen is to miss the play of the game because you were tied up swapping out a full 4GB card. I routinely shoot 6+ GBs worth of RAW+JPEG images in less than 10 minutes per group at marching band competitions. The largest bands have 200+ members, so even with 200-300 shots per group, you only have a few images of any single member.
    – Michael C
    Nov 20, 2013 at 9:02
  • but have you ever got into such situation that you are keep shotting until a 4G (or even 2G) card full? Assume you are using canon 5D mark 2 (or 7D, which is even faster that 5D2), 20M per RAW, 2G card means 100 photos. I don't think you are taking that much. You took 300 shot, but you have breaks for each several (say, 50 or more?) shots. Then you can change an empty card, or even another camera.
    – gcd0318
    Nov 20, 2013 at 15:55
  • I suggest for 'more small card is better than less large one', because when your card break, or lost, you just lost some photos on one card, but not a whole day's work
    – gcd0318
    Nov 20, 2013 at 15:56
  • No breaks in the action for the 10 minutes or so for the entire 200-300 shots. Then a runner takes that card to the sales booth where the data is transferred and the jpegs played over the screens in the booth to generate sales interest from among that band's parents/fans as they leave the stadium while I shoot the next band with another card. If we are not running the sales booth at an event I usually use 16 or 32 GB cards until they don't have room for 250 or so shots before I switch.
    – Michael C
    Nov 20, 2013 at 16:48
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    I respectfully disagree. If you are shooting in the pouring rain, you don't want to have to open your camera up to remove/replace the memory card and expose both cards and the inside of your camera to the elements. As I have already said, I believe the chances are greater for losing cards when swapping them in the field than the chances of a card becoming corrupted while in the camera. I believe the chances of the card receiving environmental damage when being changed in the field is greater than that the card will become corrupted inside the camera. We're just going to disagree on this.
    – Michael C
    Nov 26, 2013 at 4:06

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