Digital Camera Memory Cards

Which Memory Card Should I Buy?

The first thing you should know about your camera's memory card is its format. There are about 20 different formats and subcategories of formats. The user manual or the vendor's Web site can tell you which format your camera supports. Be sure to buy only that format or a memory card will not fit into your camera. The most common digital camera memory card formats are:

• CF (Compact Flash)
• SD (Secure Digital)
• SDHC (Secure Digital High Capacity)
• xD (Extreme Digital)
• MS (Memory Stick)
• MMC (MultiMediaCard)
• SM (Smart Media)

All but the cheapest digital cameras come with at least one memory card. Usually, it's enough for several days' worth of casual shooting. If you transfer photos from the camera to your hard drive or other storage media every couple of days, you don't need more memory. But sometimes you do need more memory, and better memory.

If you're going on a week-long trip, you don't want to run out of memory and you probably won't be able to empty your memory card frequently, if at all. If you're photographing a special event, you will snap a lot of photos and you don't want to run out of memory right before the groom kisses the bride. You need a memory card with lots of storage capacity. But how much capacity do you need?

How Much Storage Should a Memory Card Have?

It depends on how many photos you plan to take and how large each photo will be. Cameras generally let you specify low, medium, and high resolution for photos; the higher the resolution the bigger the photo file. Take a few photos at each of your camera's resolutions, upload to your computer, and note their file sizes. With a little math, you can estimate about how many photos your card can store.

Some cameras also incorporate file-compression technology; if that is enabled, a high-resolution photo will take up less space when stored in compressed (JPG) format than an uncompressed (RAW) photo. Here's an example of how many photos you'll be able to take with a 10-Megapixel camera and various sized memory cards:

Memory Card Tradeoffs and Gotchas

Enabling compression slows down the storage process, though, so you have to wait longer to snap the next photo. That's no problem if you're photographing flowers but when snapping a tennis match or a fashion model, you want to snap-snap-snap very rapidly. Which brings us to high-speed memory cards.

Memory card write speed is the critical factor; that is, how many bytes of data are transferred from the camera's RAM to the card's memory per second. Like optical media, memory card speed is noted in multiples of a base speed, which is 150 kilobytes per second for memory cards. So a 10x memory card writes at 1500 kilobytes/second. The fastest memory cards currently available are 150x, and they cost a lot. Most consumers do just fine with around 40x.

If your memory card works fine in your camera, but your computer won't recognize the card, chances are it's one of the newer SDHC (Secure Digital High Capacity) cards. Most computers built before 2008 will not support SDHC cards, so you'll have to connect the camera to your computer via a USB cable. It may also be possible to do a firmware upgrade to enable your computer to read SDHC cards. Check with the computer vendor to see if such an upgrade is possible.

Here's another potential gotcha when dealing with digital cameras and memory cards. I have a friend who is "technology challenged," so to speak. She couldn't understand why her digital camera would store only four or five photos. Delving into its settings, I found she had it set to use only the camera's on-board RAM. After switching on the memory card, she had room for a couple of hundred high-resolution photos. So make sure your camera's settings will enable you to use whatever memory card you buy.

And yes, the brand name you buy does matter. Digital camera memory cards are essentially solid-state RAM chips, and quality control varies from manufacturer to manufacturer. Generally, well-known brands are more reliable than generic no-name memory cards.