The film in traditional cameras is used to both record and store images. In digital cameras these two functions are performed by two separate devices. The image sensor captures the image which is then transferred to a memory storage device of some sort. This memory storage device works the way film does in a traditional camera.
They are only used to temporary store the images. At some point you transfer the images from them to a computer, erase the image data stored on the device, and reuse it.
Older and low-end cameras have built-in fixed storage that can't be removed or increased so when it gets full, you are done shooting until you download the stored images. This greatly reduces the number of photos you can take before having to erase them to make room for new ones.
Newer moderately priced and high-end cameras use some form of removable memory storage media, usually flash memory cards or secure digital cards, but occasionally small hard disks.
The memory cards are inserted into the camera via an access flap so that full cards can be replaced with empty ones easily and quickly.
Knowing how many images you can store in your camera is important as once you reach the limit you either have to stop shooting (think of it as finishing a film roll) or erase some existing images to free up space for new ones. The number of images will depend on a number of factors including:
The number of memory storage devices you have and their capacity expressed in Megabytes or Gigabytes. The greater the capacity of a memory card (say 1GB versus 512MB), the more shots you can take on that card before you have to swap it out or stop photographing.
The choice of image format and resolution used to capture images.
The amount of compression used.
Memory storage devices come in a variety of formats; they do not require batteries and do not loose images when the power is turned off.
In general different camera manufacturers like to use their own or at least different type of memory storage media format. This makes removable media formats usually not exactly interchangeable. Once you have a sizable investment in memory cards, you are locked into using only those cameras that support your format or buy a new set of cards. Make sure you check your particular camera model/manufacturer to see what you need.
Here are the details on the major memory card types:
CompactFlash Card: This is a very common memory card. Flash memory card consumes little power and takes up little space since it is about the size of a matchbox. This makes them very convenient; you can carry a number of them and change them as needed. They were developed by SanDisk Corp.
As of 2008, CompactFlash cards are generally available in capacities from about 512 MB to 100 GB, with perhaps the most popular choices in Europe and North America being between 1 GB and 16 GB. The largest CompactFlash cards commonly available currently are the 32 GB models from various manufacturers.
There are two types of
Memory Stick (MS):
This is a proprietary format from Sony developed in October 1998 and
they are used only in Sony products. These thin and flat removable
memory cards are about the length of your thumb and shaped something
like a stick of gum. Compared with current Secure Digital and
CompactFlash cards, the original MS card is incredibly slow.
In addition to the original Memory Stick, Sony came out with a Memory Stick PRO in 2003 which allows greater maximum storage capacity and faster file transfer speeds.
Sony uses a smaller card - Memory Stick DUO - in some of its supercompact Cyber-shot models. A Memory Stick DUO card is half the size of a regular Memory Stick and because of that you need an adapter to bring the Memory Stick DUO card up to the size that a Memory Stick slot or card reader can handle.
To address the size limitation and slower transfer speed of the Memory Stick DUO, Sony released in March 2008 a Memory Stick PRO Duo version with capacity of 16 GB. There are to release a 32 GB version in 2009.
Secure Digital (SD) Card: Secure Digital (SD) cards are smaller than CompactFlash cards and have a low power consumption. They are used in over half of current camera models and can also be used in other gadgets like PDAs, media players and mobile phones.
Standard Secure Digital card capacities range from 4 MB to 4 GB, and for high capacity SDHC cards from 4 GB to 32 GB as of 2008. Note that since the high capacity SDHC card is a relatively new format, this type of card might have compatibility issues with some older camera models that cannot read this format.
MultiMediaCard (MMC): SD and MMCs are nearly identical on the outside, but MMC cards are slower, less secure and are physically thinner than SD cards. They are about the size of a postage stamp and are used in a few pocket cameras. A MultiMediaCard can fit into an SD slot, but an SD card cannot fit into an MMC slot. MMCs are usually compatible with cameras that can use an SD Card.
xD-Picture Card: Olympus and Fuji jointly developed the xD-Picture Card, which has an ultracompact design and storage capacity of up to 8GB. These cards are compatible with different digital camera brands and are generally fast in comparison to the Memory Stick (MS) format.
The microdrive storage
device was pioneered by IBM and typically offers larger
storage capacities at a cheaper cost per megabyte. They use more
battery power though, create more heat and have a higher risk of
failure because they contain moving parts.
Microdrives like Hitachi's Microdrive and Sony's Compactvault are high speed, high capacity hard disk drives but are so small they can be plugged into a Type II CompactFlash slot on a digital camera or flash card reader. (Type I CompactFlash slots are thinner).
Memory Storage Type:
Dimensions in mm:
for most advanced dSLR and some compact cameras
|Most Canon, Hewlett-Packard, Casio, Minolta, and pre-2002 dSLR Kodak||42.8 x 36.4 x 3.3|
stick of chewing gum
Used almost exclusively in Sony digital cameras, camcorders and other electronic equipment
|50.0 x 21.5 x 2.8|
Used with most compact cameras (except Fuji, Olympus and Sony) and some enthusiasr dSLRs
|32.0 x 24.0 x 2.1|
and physically thinner than SD cards
with cameras that can use SD Card
|Used in a few pocket cameras||32.0 x 24.0 x 1.4|
|xD Picture Card||
Format aimed at very small digital cameras, developed by Olympus, Fujifilm, and Toshiba
|25.0 x 20.0 x 1.7|
power and create
|Popular in high resolution dSLRs, PDAs and MP3 players||42.8 x 36.4 x 5.0|
Here are some additional considerations to take into account with regard to memory storage devices and how your camera stores images:
The digital SLR takes the bits coming out of the image sensor and conducts them to a special high-speed type of internal memory called a buffer. Thanks to the buffer, you can continue taking photos while the camera deals with transferring the most recent images to the memory device. The size and speed of the buffer determines how many pictures you can take in a row. Digital cameras generally let you take 5 to 30 shots consecutively, and have continuous shot (burst) modes good for 2.5 to 10 frames per second for as long as the buffer holds out. Thus having a faster, larger buffer is better.
Memory storage cards have their own writing speed, which determines how quickly the card can accept images from the buffer. Many companies sell regular and high-speed versions. There is no standard measurement for the speed, so you can find memory cards labelled 40X, 80X, 120X, 133X, Ultra, or Extreme. Most of the time, you will be concerned with the speed of your memory card speed only if you are photographing sports and want to take many pictures in a row.
As we discussed earlier memory cards store the images captured by the digital sensors in your camera. Different camera manufacturers favour different card types. Thus it is important that you check which type your camera uses before purchasing additional cards.
The greater the capacity of a memory card (say 8GB versus 512MB), the more shots you can take on that card before you have to swap it out or stop photographing. However, the higher the capacity of the memory card, the more it will cost.
When you first buy a memory card or use it in a different camera you should format it. Every camera that accepts these cards has a Format command listed somewhere in its menus. Formatting prepares the card for use in a camera and reformatting it when you change cameras just ensures the card will be accurately written to and read in that specific camera. You may also find that formatting a card that has developed problems will also fix it. Just be aware that the Format command will erase all of the images from the card. Should you ever do this by mistake, there is digital image recovery software available.
If you download images from removable media to your computer (as compared with downloading straight from your camera via a USB cable), your computer must be able to accept these memory storage devices, too. Some machines come equipped with card readers on their front (usually next to the USB ports), and sometimes you need to use an external card reader.