In all of the excitement of getting a new camera, there is usually a need to get a new memory card to go along with your purchase. If this is your first digital camera, then you can't take any pictures without a new card. Even if you already have a card of the correct type, digital cameras, and especially digital SLR's are recording very large image files that may demand a larger capacity card.
There are so many types and specs for memory cards, but selecting one that will work well with your new DSLR doesn't have to be hard. You basically have to navigate the following criterion: memory card type (form factor), capacity, and speed. Along the way, other questions may come about; I will discuss this all here.
Memory cards for Digital SLR cameras come in two main form-factors: SD (stands for 'secure digital') and CF (Compact Flash). SD cards are smaller in size than CF cards. What SD cards gain in smaller size, they give up in maximum capacity and maximum read/write speeds.
CF cards have traditionally been used in professional level cameras (where higher read/write speeds are necessary), whereas the SD memory card form factor has been for smaller pocket digital cameras. Over the past few years, SD cards are starting to be used more and more in Digital SLR cameras. Models around or below the $1,200 pricepoint almost assuredly use a SD type card. Professional level and older DSLR's still use CF cards, but some models (like the Nikon D800 and D800E) are incorporating dual card slots where one of the slots is for CF and the other is for SD.
I am using the term SD, but know that all new DSLR cameras now have video recording capabilities and SD cards now have two new variants. The first is SDHC (Secure Digital High Capacity), which is a format that allows larger capacity cards (up to 32GB) that play well with the write speed requirements of a camera that can record video. There is now an even newer format called SDXC (Secure Digital eXtended Capacity) that allow for capacities greater than 32GB, like this Sandisk Extreme 128 GB SDXC Card.
The topic of what capacity memory card you should choose for your Digital SLR deserves a separate discussion. However, the basics are that the size that is best for you depends on: the filesize of the images your camera produces, the number of pictures you would like to take on a single card, single card vs. multiple cards, and how much video you want to record.
The instructions for every camera model (available as an online pdf download) includes a chart that gives the user an idea of how many images can be recorded at various image qualities (raw, jpg fine, jpg small, etc.) and the duration of video that can be recorded for each GB of card capacity. If you can look-up this information, you will be able to tell how many shots and/or minutes of video you can fit on a given size of card.
Again, it is tough when you are starting out to know exactly how you will use your camera; how much video vs. pictures, what image quality, and how many pictures between card downloads. Having said all this, if you are looking for a SDHC card, the sweet spot for price vs. capacity seems to be with the 32GB cards and that would be my recommendation.
For CF cards, there are more choices for memory with the larger CF form factor allowing for larger capacities. The price to capacity sweetspot seems to be 16gb, 32gb, or 64gb. Pick a size based on how you plan to shoot and the budget you have for your card.
cards are rated on their read and write speed. Write speeds are critical for the performance when the card is in your camera (how fast data can be moved into the card from your camera). Read speeds are applicable to getting the data off the card and into your computer.
SD and SDHC cards are often separated into speed categories of 'Class 6', 'Class 8', or 'Class 10'. The class number represents the minimum write speed for a card. A class 10 card has a minimum write speed of 10 megabytes per second.
CF card speeds are usually expressed simply in megabytes per second. If comparing one card to another, care needs to be taken to make sure the number advertised is read, write, or both read and write. Some cards state an inflated speed that is the maximum read data rate; the write data rate (applicable to how it will perform in your camera) may be lower.
There are three instances where a fast card can help you. The first is if you shoot long burst of pictures. It is possible to fill up the camera's internal memory when shooting an extended sequence of fast shots. Once the camera's buffer is full, the camera shoot rate will slow down. How long until the camera can recover and shoot full speed again will depend on the write speed of the card.
The second situation where card speed is critical is when shooting HD video. To be able to record HD video, most manufacturers recommend using a class 6 card or faster.
The third scenario where a fast card is nice is to speed up the transfer of pictures to your computer.
For SDHC, I would recommend a class 10 card. The cost gain over a class 6 card is minimal and the slight increase in cost is worth the performance gains for video and continuous shooting.
For CF cards, every manufacturer is divided into broad categories of fastest and down the line. For example, Sandisk Extreme Pro is a step above their Extreme series. The fastest card series are usually a waste of money for most camera users. It is best to go a step down and save some money. If you shoot sports or wildlife where continuous shooting is a must, then you should consider moving up to the fastest class cards.
I am usually all for saving money, but in the long run, I don't feel that the risk is worth it to save some money by going with a no-name or generic memory card. Those few saved dollars will be quickly forgotten if you are ever faced with a corrupted card that destroys your pictures. You will soon learn that the true value in any card is being confident that it will securely hold your pictures.
I personally stick with a single brand: Sandisk. I have never had any problems with their cards as far as corruption or lost photos. While I have not had direct experiences, Lexar is also a good brand of cards.
For cameras that take SD format cards, I recommend a Class 10, 32 GB card. If this does not offer you enough capacity, you can consider buying multiple as it will probably be more economical than jumping to the more expensive SDXC cards.
For CF format cameras, I recommend Sandisk Extreme series cards (or equivalent speeds by Lexar) in a size that best suits your shooting needs.