Thoughts on memory cards
Today's cameras use digital media cards, or as I like to call them, the never-ending roll of film. Solid state memory storage devices that are reliable and nearly indestructible. As technology gets better, they also get cheaper. But there are differences in memory cards and getting the right memory card for your needs is important. Since the type of camera you use determines the type of card you need to have we'll just discuss the other two important factors in selecting a memory card; capacity and write speed.
CapacityAs camera sensors get progressively better they also start demanding more memory. Specially if you have a camera that can also shoot video. Today's cameras have outgrown the 256MB storage capacity cards of yesterday. Even some of the current point and shoot compacts will laugh at a 2 or 4 gigabyte card. Depending on your shooting style many pros have advanced to the higher capacity 16 and 32 gigabyte cards, skipping right over the 8GB cards. If you are having a hard time determining where you fit in here are some pointers.
- File size versus download time: If you are a casual shooter who takes your camera out randomly and sporadically throughout the month and you shoot in JPG for internet sharing or small prints a 4GB card will do just fine. Move up to shooting RAW and you have literally doubled the memory requirement then an 8GB card will work. However, you have to be diligent and download your images before you run out of room. If you shoot more regularly have an extra card handy.
Advanced hobbyists who take more images need to analyze their current usage. If you are blowing through a 4GB card before the end of the day then an 8GB may do you better. Of course you will need to set some time at the end of the day to clear your images. Again, a big factor is whether you are shooting in JPG or RAW. You will roughly double the number of images with JPG than with RAW.
Pros who shoot hundreds of shots within hours will definitely benefit from higher capacity memory cards. While 8GB cards will be fine for short studio sessions, a more realistic assumption is to use 16 or 32 gigabyte cards. Specially if you are shooting a lot of action such as sports or news events.
- Capacity versus loss: Memory cards use solid state technology. Once written to the card the data is permanently stored until something causes it to change. There have been cases of cameras dropped in water or lost in snow banks only to be recovered later with the image files intact. Erasing files is also a slim chance. The bigger threat is loosing a card from carelessness or theft. They're small, light and easy to misplace; specially SD cards.
One school of thought is to spread your images from a shoot over several lower capacity cards. While this means changing out cards more often it guarantees you won't loose all your images from the shoot. If you shoot 400 frames distributed over four cards and you loose one, all is not lost. Is it painful loosing that one card? Yes, but it's better than loosing an entire day's shoot.
On the other hand, by having one large capacity card with all your images on it you no longer have to keep track of multiple cards. Specially if you are not very organized. It also avoids the dreaded "card full" message in the middle of shooting something important.
You can also become someone's hero by having an extra card to lend when someone else encounters any of these scenarios. It's always best to be over prepared rather than under prepared. In a working situation it can mean the difference between getting paid or getting fired.
Write speedWhile having enough physical space is important, a bigger factor for many shooters is the card's 'write speed', or how fast the data gets transferred from the camera to the card. With any computer, native memory is always faster than external memory. The same goes with cameras.
- Write speed to frame rate: You camera has a built in memory that it uses whenever you press the shutter. It is a temporary buffer it uses before transferring the data to the memory card. The faster your card can transfer the image the faster you can shoot the next frame. While this is not critical for most single frame shooting situations it does become important for high speed continuous frame shooting. If your camera takes eight frames per second but your card can only transfer five frames per second you start getting a lag. Before long your camera will freeze up until it has had time to clear its buffer.
- Decoding write speeds: Most of us are familiar with the labels on memory cards; SD stand for secure digital while CF stands for compact flash, the two most common camera storage types (others include mini SD, micro SD, MemoryStick and SmartMedia). A number followed by MB or GB lets us know the capacity of the card (i.e. 512MB, 32GB). Many cards will also have the write speed indicated on the label written as a transfer rate or a multiplier factor.
Some cards will list transfer rate in MB per second while others will list it as a multiplier (i.e. 600X). Here is a table that may help sort things out but keep in mind the numbers posted are read rates and not write rates. Writing transfer rates can be up to one third slower;
|133X||30 MB/s read rate|
|400X||60 MB/s read rate|
|600X||90 MB/s guaranteed read rate|
|1000X||150 MB/s read rate|
CompatibilityNot all cards are created the same. Not just in shape and size, but in technology as well. Current technology has pushed the storage envelope considerably. SD cards have gone from the standard and limited regular format to the high capacity SDHC format. While newer devices can read old technology cards, new technology cards don't work in old devices. My old Kodak EasyShare uses regular SD cards but will not recognize a SDHC card. Keep this in mind when figuring out what you need. Your camera's manual should have the specifications.
As I mentioned above, the type (and speed) of the card you get is highly dependent on your shooting habits. For a simple way of looking at all that information above think of it this way; the faster you shoot the faster the card. The more you shoot, the bigger the card. Just understand that bigger and faster also means more expensive. As of this writing Sandisk has a
Here is a link to Sandisk's website that illustrates the storage capacity of typical memory cards in relation to image size (megapixels); "Number of pictures that can be stored on a memory device"
Lexar, another leading manufacturer, also maintains a lot of great info on their site. You can read their "Frequently asked questions" for more info.