House of cards

Both CF and SD cards use the Windows Fat file system. CF cards larger than 2GB use Fat32, as do SD cards larger than 2GB and Secure Digital High Capacity (SDHC) cards. Larger cards may not be compatible with your camera, so before buying one you’ll need to check your camera and card reader support the Fat32 file system - more about that later.

What size cards should you use? In price terms, there’s little to be gained, or lost, by going for larger capacity cards. An 8GB card in a particular manufacturer’s range will be about the same price per gigabyte as a 2GB card.

On the plus side, you’ll get a lot more pictures on an 8GB card before you need to change it. The drawback is that if a card fails, or you accidentally format it, you will lose more pictures.

Compatibility
There are two types of CF: type I and type II. Type I cards are 3.3mm thick and type II are 5mm thick. Type I cards are more common these days; CFII cards were used in the past for larger capacity cards and microdrives. Many cameras that use CF media will accept both types, but some recent models, such as the Nikon D700, only take type I cards. Given that nearly all cards these days are type I, this isn’t something you need to worry about.

The only other CF card compatibility issue you need to consider is size. You’ll only be able to use Fat32 cards of 2GB and larger in more recent cameras. My Canon EOS 20D, which was released in 2004, supports Fat32, as do most DSLRs manufactured from the beginning of that year. If you use a card reader to transfer images to your PC, you’ll also need to check that it is compatible with the larger cards.

The situation with SD cards is a little more complicated. There are two versions - SD and SDHC. SD cards have a maximum capacity of 2GB, SDHC cards have a maximum capacity of 32GB, making them ideal for video use as well as high-volume photography. Older cameras that use SD cards won’t be compatible wi th SDHC cards. The only exception is where a manufacturer has released a firmware update as, for example, in the case of the *ist DL and K100D from Pentax and some Canon EOS-1Dx models.

The situation was complicated by the introduction of 4GB SD cards, which had limited compatibility in both cameras and card readers. If you’re planning to buy large-capacity media and you’re concerned about compatibility, check your camera documentation. If you can’t find anything there, try the card makers’ websites. There’s a compatibility checker for Sandisk cards at www.sandisk.com/Compatibility.

Speed freaks
One of the biggest factors affecting media cost is write speeds, but there’s little point in paying a premium for fast cards if you either don’t need the speed or your camera can’t make use of it. Most DSLRs have a generous buffer capable of storing several full-resolution Raw image files (and even more JPEGs) and it’s not until this fills up that the card speed becomes important. Once that happens, unless your camera can write at speeds comparable with the card, you won’t get the kind of throughput you’re paying a premium for.

The Canon EOS 20D can shoot 5fps (frames per second) and its buffer can hold around 23 full-resolution JPEGs, so I can shoot at least 23 frames at 5fps before the buffer fills up and I have to wait for some of those images to be written to the card. In practice, it will be more because some data will have written to the card during shooting.