Size and Speed Matter more than
You Might Think
by Jim McGee
If you buy a big megapixel digital SLR figure on buying some big memory cards. This is especially true if you plan on doing any of your shooting in the camera's raw mode.
A 512mb compact flash card will hold 50 raw images on a D100 or 149 images in JPEG fine mode. That sounds like a lot until you start shooting in someplace like Zion or Yellowstone. After all 149 images is only the equivalent of 4 rolls of film. How often do you plan to upload to a laptop? Do you really want to lug a laptop and it's extra weight along when you're hiking up a trail? Trust me the answer is no. Even keeping one in the car is a pain. And I'll guarantee the moment the card is filled you'll be presented with the photo opportunity of a lifetime.
When traveling most photographers burn through rolls of film. After all you've paid all the money and taken the time to get there - film is the least of your expense. So when I go out with a digital camera I want to know that I've got enough film, er, memory to get every image I want. I don't like editing down images in the camera. That little LCD screen on the back is a pretty lousy tool for judging image quality. I prefer to do that on a laptop back in the hotel after a good dinner.
So how much memory do you really need?
The answer is it depends. It depends on your shooting style. It depends on your subject matter. It depends on how long you'll be traveling. Finally it depends on whether you'll be taking a laptop or some other storage device along or if you'll wait until you get back to upload your images. One gauge is to think about how many rolls of film you'd normally take along on a similar trip. Figure out how many frames that would be, and then figure out how many images you can get onto a card in the mode you prefer to shoot and you've got a pretty good idea.
Remember not every image has to be shot in raw mode. Photos of you and your buddies at dinner probably won't rate a wall size print. So shooting in JPEG normal mode for tourist shots will save on disk space.
One other thing to consider is whether you want one huge card or several smaller cards. At PMA Lexar announced new 2GB and 4GB cards, and cards of 512MB and 1GB are already available. It's my paranoid preference to break up my shooting among several cards. This way if one card fails I'm not dead in the water and I haven't lost all of my images. Though I must admit that failures of CompactFlash cards are rare.
The next question is speed. How fast do you need? Again it depends. Are you shooting a lot of action sequences or sports in high-res mode? If so you want the fastest card you can get. Otherwise the frame buffer may fill up and you'll be stuck waiting for the camera to write images to the memory card while the action continues around you. But that speed will be wasted if you carefully compose landscapes while standing upon a mountainside. The downtime between shots for the average landscape photographer will allow more than enough time for the camera to save the images.
There is one other time when the speed of your memory card comes into play. That's when you're uploading images. The faster the access speed for the card the faster it can kick those images up to your laptop or desktop. Remember your computer treats the card like a disk drive if it's in a card reader or PCMCIA adapter. Those speed ratings on the card are analogous to the speed ratings on a CDROM drive1. To get a feel for what they really mean check out the chart at the end of this article.
Common speeds for CompactFlash cards today are 12x, 16x and 24x. But at PMA this month Lexar announced a 512MB card rated at 40x speed! For the Digital camera test between the D100 and SD-9 in this issue I used 24x cards. While I wasn't shooting action I didn't find myself waiting for the camera when shooting in raw mode. If I were shooting action with this setup I'd probably shoot in hi-res JPEG mode to reduce file size and write time. But if you're considering cameras that create REALLY big image files such as the Canon 1Ds and Kodak 14n you'll want to seriously consider ever faster write speeds.
Another consideration is a new feature called Write Acceleration (WA), supported by Nikon, Canon, Kodak, and Lexar. As the name implies it increases the speed at which the camera writes to the memory card by simplifying the communication between the card and the camera.
Just to make things a little more complicated Sandisk doesn't use the X-rating system. They have standard and Ultra cards. The Ultra cards, which they recommend for high-res cameras, have a write speed of 2.8MB/second, which would be the equivalent of a 19x card in the X-rating system.
You'll also find in-store brand memory cards at some major retailers. Look closely at the packaging and you'll find either Lexar or Sandisk make most of these cards. The two brands are price competitive and reliable. We've not heard reports of any significant problems with either.
These cards tend to be pretty rugged. Cold and heat don't seem to bother them very much and stories abound of people who've put them through the wash by accident and the cards still worked after they'd been dried out (though we wouldn't recommend this kind of treatment). The cards do occasionally fail and there are instances where images become corrupted on the cards.
Moose Peterson, who's shot more digital images than anyone I know recommends reformatting each time you load a fresh card into the camera as a precaution.
Next month we'll feature an article on how to recover images if the worst happens to your CompactFlash cards.