Just like batteries, it is a very, very good idea to buy at least one spare memory card for your digital camera. Even if you only ever buy one, the range in price is such that it's easily possible to spend four times as much for what is effectively the same thing.
There are several different types of card available; compact flash (CF), secure digital (SD), memory stick etc. The different types of card function exactly the same way, they just store computer files similar to floppy disks or CDs, the only practical difference is which cameras they fit.
Except for smart media (whose capacity is limited to 128 Mb) all the others have been getting bigger and cheaper per Mb since they first came out and the rate of change is, if anything, increasing.
Amongst these changing prices, a few things remain consistent. At any given time, the cost of a card is affected by several things. The place you buy it, the name on the label, its capacity and its speed.
Where to buy
For some reason the range of prices you can pay for exactly the same item, depending on where you buy is, in percentage terms, greater for memory cards than most other things. It is definitely worth while to shop around for these items.
Labels
An even greater difference in price exists between generic (i.e. Unbranded) cards and those with a well known brand or camera maker’s name on the label.
Except for a few specific exceptions, any card of the right type will work the same way. These are solid state devices and you would therefore expect that if they work out of the box, they will continue doing so at least another several thousand times. You can test a card by simply filling it up with pictures and viewing them.
If they don't work properly first time, they probably never will. If they do fail,
it's usually catastrophic and without warning -
Capacity
A digital camera memory card’s capacity is measured in Megabytes (Mb) or Gigabytes (Gb). 1 Gb = 1024 Mb. How this relates to the actual number of pictures stored depends on your camera and its settings for image size and quality. Your manual should have the information. It may also tell you if there is a maximum size of card for the camera. If so, a larger card would be a waste of money and it may not work at all.
How many?
The capacity of a digital camera memory card only tells you how much space is available, not how many pictures it can hold. That depends on your camera and the settings you are using for image size and quality.
It’s not unusual to get as many as 10 times more images on the same card in the same camera simply by changing these two settings from maximum to minimum.
Only if these settings don’t change will a card with twice the capacity will hold roughly twice the number of pictures.
Most cameras save images in a (jpeg) format that reduces the size of the file. Trouble is that the actual file size is not fixed but depends, to some extent, on the image itself.
This is why you can never tell exactly how many images can be stored and the larger the card the more inaccurate your camera’s counter may seem.
Save money on memory cards