Premium cards versus budget cards
There are many brands of Flash memory cards, and prices for all types vary widely. Performance also varies, and it is usually the case that cheaper cards do not perform as well as more expensive ones. Premium brands such as SanDiskâ€™s Ultra and Extreme, Lexarâ€™s Platinum and Professional and Kingstonâ€™s Elite and Ultimate cards routinely out-perform budget-priced cards in tests, and it is generally a good idea to spend a little extra money and buy these more expensive types of card. The read/write speed of your memory card can have a significant effect on your cameraâ€™s performance, particularly in shot-to-shot times and continuous shooting, and in the speed of transferring data to your computer. Cards from cheaper brands may also prove to be less reliable than premium brands, many of which come with lifetime guarantees.
So how many pictures can I take?
The total number of pictures that can be stored on a memory card is a difficult thing to quantify for several reasons. Most digital cameras store images using the JPEG file format, which compresses image data to save space. The degree of compression varies depending on the nature of the image, and so the file size can vary widely from shot to shot. For a typical 7MP compact camera on the maximum quality setting, file sizes can vary between approximately 2MB and 4MB depending on the content of the shot, although they will usually average around 3.5MB. As well as this most cameras have a range of quality settings, which alter the degree of compression so that more images can be squeezed onto the memory card, although with high-capacity memory cards now so cheap itâ€™s usually possible to use the maximum quality setting at all times. For the same typical 7MP compact camera, files at the lowest quality setting can be as small as a third of the size of shots at the maximum quality setting. Because of these factors, 1GB card in our hypothetical typical 7MP compact camera may hold as few as 200 or as many as 800 shots depending on the quality setting and the subject matter.
Even for cameras that have a RAW mode, the total number of shots per card may vary, because some cameras use a compressed RAW format, which may have a variable compression rate. The only cameras for which the total capacity of the card can be stated are those few top-end professional cameras that use an uncompressed file format such a TIFF.
And what of the future? The price of memory chips continues to fall, and high capacity memory cards become ever cheaper on an almost daily basis. Today itâ€™s quite possible to find premium-brand high-speed 1GB SD cards for as little as Â£12, and itâ€™s almost inevitable that they will get even cheaper as maximum capacities get ever larger, driven by the seemingly unstoppable progression of ever more powerful camera sensors. In the meantime several companies are working on new types of data storage, including optical holographic memory which could lead to memory cards that can hold terabytes (1 terabyte = 1,000 gigabytes) of data. One thing is for sure, weâ€™re not going to run out of room any time soon.