As far as DSLR and CSC cameras are concerned, memory cards fall into two main types - Secure Digital, or SD for short, and Compact Flash, or CF. SD cards are more common in entry-level cameras, while the thicker, stronger and more durable CF cards are more usually found in enthusiast or professional level models.
If you are used to a digital camera your camera probably has some built in memory. Digital SLRs tend not to have any memory built in so you will need to have at least one card before you can use your camera.
One question that gets asked a lot is should you buy one memory card with a large storage capacity or two or more cards with smaller capacities. With no built in storage available for emergencies it is a good idea to have at least one card in reserve as well as your main card. While memory cards are very reliable if handled with a little care, there is always the possibility that a card will fail.
More advanced Digital SLRs can have more than one memory card slots. This allows you to set the camera up in different ways. For example a camera may allow you to use one card for recording video or another for stills. You may also be able to opt for writing Jpeg images to one card and RAW images to another simultaneously.
Digital memory cards can hold many hundreds of pictures, but just how many will depend on the resolution of your camera (how many megapixels it uses), whether you are shooting in JPEG or RAW format, and, of course, the capacity of the card. Cards come in many different capacities, from 1 or 2 gigabytes up to as much as 64 gigabytes. Most SD cards nowadays are the newer SDHC format, where the HC means High Capacity, and the latest generation SDXC cards will eventually be able to offer even higher capacities.
Memory cards are fairly robust, but still need to be handled sensibly. It is worth keeping them in a clean, dust free environment when they are not in use. As well as helping to ensure a long working life for the card it also helps to minimise any transfer of dust and dirt to the camera.
Digital SLR Basics
Digital SLRs and Digital Cameras Key Differences
Digital SLR or Compact System Cameras
Digital SLR Handling
Help for Beginners
Lenses and Accessories
Buying a Camera Lens
Digital SLR Accessories
Learn More About Features
Resolution and Sensor Size
Manual Exposure Modes
Help With Tricky Lighting
Live View and Articulated Screens
Depth of Field Preview Button
Current and Recommended Models
Summary of Current Models
Recommended Digital SLRs
Digital SLR Guide Author
This guide was written by Ian Younger
As well as the capacity of the card you need to check how fast the camera can record data onto the card and how quickly the data can be copied from the card onto your computer. The earliest memory cards had transfer speeds quoted using a similar system to that used for describing transfer rates on CD-ROMs, and a speed of around 150 kilobytes per second was standard.
As manufacturers began to improve on this, speeds were as, for example, 10x, meaning 10 times the speed of the earlier cards, or 1.5 megabytes per second. Transfer speeds now have become so fast that a new classification system is used for most SD cards, and they will be described as Class 2, Class 4, Class 6 etc. Class 2 has a transfer speed of 2 megabytes per second, Class 4 is 4 megabytes per second and so on.
With entry level Digital SLRs you may not see a great difference in the speed at which photos are written to a memory card, even if you are using a card capable of being written to at high speeds. Therefore it is worth checking with the manufacturer of your Digital SLR if there are any benefits in buying more expensive, high speed cards before you commit to paying more.
One area where you may need a faster card even with an entry level Digital SLR is if you are planning to record High Definition movies.
There are a wide variety of brands available. Over the years I have not noticed any significant difference in either reliability or speeds offered by different brands. As ever it is likely to be a wise decision to avoid deals that look too good to be true. There is no need to buy a memory card made by the manufacturer of your Digital SLR.