Buying a memory card
Buying a memory card is the last thing you need to do before you can start taking photographs. Having already spent time deciding on a cameras the memory card is usually a choice that photogrpahers want to get over and done with quickly, which is quite understandable as it is only the recording medium.
Mercifully there are not many considerations. But consider them you must and these considerations are.
What type of card (This is easy).
How much storage (Down to the length of your photo shoots).
What write speed (decided by the performance of your camera)
Types of memory cards
Compact Flash, Secure Digital and Memory Stick
The above types of card form the basis of literally all card fits. In particular Compact Flash and Secure Digital with Memory sticks being a their own fitting from Sony which they have used in a variety of their electronics goods.
There used to be a bit of a standards war but this has very much settled down now.
There are other types of card such as 'micro SD' but these are a type of Secure Digital card and can be used with a plastic carrier.
Your camera will most likely take one of these fits. If it doesn't, your choice will be limited but you should still heed the following points.
Storage space
How many exposures
Like all digital recording mediums, memory cards have a certain level of storage space. More storage means more cost but its usually not proportional. However before you buy the largest card you can find or afford, consider that if the card corrupts you lose that many more photos. For those going on holiday, do they REALLY want to risk losing all their holiday shots because they were on the same card?
How big are the images, 10Meg, 25Mg?....How often will you take the photos off the card and into your PC/mac.... If its often say after an evenings shoot then a massive card may well be pointless. Will you be shooting dozens of frames per minute? I shoot live music. Maybe 2 shots per minute. I find I am unlikely to fill more than one 4 gig card per average shoot. I have 4 x 4Gb cards for festivals etc... If I have a PC with me then the PC can retrieve photos while I continue to shoot.
The size of the cameras memory card decision is very much down to your workflow.
Memory Cards read and write speeds
How fast can your camera save images to a memory card.
To achieve optimum performance from your digital camera you need to match the card's read/write speed to the upper limit of the camera.
The cheapest card in your chosen size and fit may not be the best choice for you and likewise buying a blisteringly fast card may be a waste of your resources.
Sandisk used to call their cards Ultra, UltraII, Extreme III, Extreme IV etc which denoted speed.
Normal Sandisk (blue card) 3MB/s- Low end compact cameras
Ultra II 15mb/s (soon to be 'Ultra') - High end compact cameras
Extreme III 30mb/s(soon to be 'Extreme') - D-SLRs
ExtremeIV 45mb/s(soon to be 'Extreme Pro') - Pro D-SLRS
If your PC or mac does not have a memory card slot (many do btw) then you will require a USB card reader.
Sandisk USB 2.0 readers work at 30MB/s and 35MB/S. If you had extreme IV cards then you would need a Sandisk Firewire 800 reader, however Apple Mac compatibility has in the past been problematic. USB 3.0 is just around the corner and it is likely that Sandisk will release a faster USB reader.
Speed classes also describe how cards handle video -
Sandisk have supplied the figures below to help with establishing which memory cards you need. Image file sizes vary betweeen manufacturers and cameras so check you camera manual for a more conclusive details.
Average Number of Raw Images
When considering buying memory cards you may wish to refer to this table
If your image file size is approx 24mb
64GB - 2080 images
32GB - 1040 images
16GB - 550 images
8GB - 260 images
4GB - 130 images
If your image file size is approx 18mb
64GB - 2880 images
32GB - 1440 images
16GB - 7200 images
8GB - 260 images
4GB - 130 images
If your image file size is approx 14mb
64GB - 3840 images
32GB - 1920 images
16GB - 960 images
8GB - 480 images
4GB - 240 images
If your image file size is approx 10mb
64GB - 5120 images
32GB - 2560 images
16GB - 1280 images
8GB - 640 images
4GB - 320 images