How to Buy a Memory Card for a DSLR Camera

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How to Buy a Memory Card for a DSLR Camera
A memory card is an essential component of a DSLR camera. DSLR cameras enable high-quality photos to be taken and stored in different formats. The higher the number of megapixels, the better the quality of the photos, but the larger the space needed on the memory card. DSLR cameras allow users to change the format in which the photos is stored. Most amateur photographers will use JPEG format, but professional are more likely to use RAW format, which takes up considerably more space. It is also possible to vary the size of the photos with low, medium and high resolution options, but the higher the resolution the larger the file.

There are different card formats, but the vast majority of DSLR cameras use Compact Flash or SD cards, determined by the manufacturer.

Storage Capacity and Card Speed

There are two aspects which need to be considered: the storage capacity and the card speed.

Storage Capacity

Storage capacity determines how much space is available to store photos and/or video. A 4GB card will have a storage capacity of 4096MB. The exact number of photos that can be stored on the card depends on the resolution of the photos, and the format. Video also takes up a considerable amount of memory.
Most cards range from 4GB up to 32GB, although a few cards have higher capacity. Many manufacturers have tables available on their website to estimate how many photos can be stored on a given card.

What Size of Card to Choose

The best size of card to choose will depend on individual circumstances. An amateur photographer, shooting at a medium resolution, will need a lower capacity card than a professional shooting images in RAW. The length of time before downloading can be done is also important; for example, a photographer who is away for several weeks without an opportunity to download will need a large capacity card.

Card Speed

There are two elements to the speed of a card: read speed and write speed. Read speed determines how quickly photo data can be read by the computer. Write speed determines how quickly the data is transferred onto the card after the photo is taken. A high write speed is especially important for photographers who use burst'functions, when multiple images are taken very quickly, such as in sports or wildlife photography.

Two Kinds of Speed Indication

There are two ways in which card speed is calculated.

Multiplication Factor

The multiplication factor of a card is calculated based on CD-Rom speed of 150KB per second. The higher the multiplication factor, the faster data can be processed. Therefore a 500X multiplication factor means the data is read at 74MB file in one second.

SD Card Class Rating

SD cards use a class rating system to classify card speeds. For example, a Class 2 card has a minimum write speed of 2MB per second (2MB/s), broadly equivalent to 13X, and a Class 4 card has a 4MB/s speed. The card may state a higher rate, but that will be the possible rate rather than the sustainable rate. Manufacturers' websites give more detailed information about the class rates.

How Does the Speed Affect the Price?

The higher the card speed, the more efficiently the card operates, so faster cards are more expensive.

What is the Fastest Speed?

The fastest Compact Flash cards have speeds of around 90MB/s (600X).
SDHC cards are generally slower than Compact Flash, with top speeds of around 30MB/s (200X) in a Class 10 card.
In all cases, card speeds can be maintained at the optimum rate by regularly formatting the card, using the camera settings, to clear any residual data which may inhibit the efficiency.

Which is the Best Speed Card to Choose?

The optimum card speed depends on the kind of photography and the camera capacity. Photographers with the latest equipment, shooting in RAW need a faster card than an amateur who photographs occasionally. However, only high-specification DSLR cameras can truly take advantage of the fastest speeds, so consider the age and type of camera before investing in a very high-speed card.

Different Kinds of Memory Card

There are three different kinds of cards which are likely to be used for DSLR cameras: Compact Flash, SD cards, and UXD cards. The vast majority use Compact Flash or SD cards.

Compact Flash Cards

Compact Flash cards were first introduced in 1994. With a high storage capacity and fast processing times, nowadays CF cards tend only to be used in higher-specification SDLR cameras. There are two types of CF card; Type I and Type II; most cameras can accommodate either.


General features

Relatively thick and durable when compared with SD Cards.
Pin holes on one edge to match with the camera pins


About 3cm square

Storage capacity

Ranges from 4MB to 32MB

Processing speed

Calculated in MB/s.
Ranges from 30MB/s to 60MB/s

Ultra Direct Memory Access (UDMA) Compact Flash Cards

These higher-specification CF cards have a very fast speed and larger storage capacity. For example, a UDMA 6 card has a 64GB memory, and processing speed of 90MB/s. However, a compatible card reader is required to download photos.

General features

As a standard CF card


Same as standard CF card

Storage capacity


Processing speed

Graded UDMA 1-7 (25.7MB/S – 167MB/S)

UXD Cards

UXD cards represent the next generation of CF cards. They are smaller than CF cards, but larger than SD cards. As yet only the Nikon D4 uses this format.

Secure Data cards (SD Cards)

Again, there are several kinds of SD card. They are small and lightweight (similar to a postage stamp).



Standard SD

The earliest SD card.
Usually up to 2GB capacity

Secure Data High Capacity (SDHC)

Up to 32GB capacity
Same size and shape as standard cards, but a different format. New cameras will read both kinds, but older cameras will not read SDHC format.

Secure Digital 'Xtra Capacity (SDXC)

Similar to SDHC cards, but much higher capacity (predicted up to 2TB), and faster processing speed.
Only recognised by newer cameras
Only recognised by some computer operating systems e.g. Windows 7 or Mac OSX Snow Leopard or above.

UHS-I Standard SD

The latest release from Sandisk, with very high read and write speeds. e.g. Class 10 cards predicted to have write speeds of up to 80MB/s

Wireless SDHC cards

These SDHC cards can transmit data wirelessly to a computer or other compatible device. They can also upload photos directly to social media sites e.g. Facebook, Flickr.

Other Card Formats

Some manufacturers have their own card format, such as Sony, but their cameras usually take SD cards as well.

Potential Problems

Problems with memory cards are rare, but if they occur, precious photos may be lost, so taking steps to minimise the risk will help ensure photos stay safe.



Physical damage

CF cards are less likely to be damaged than SD cards, but careful handling should eliminate damage.

Corrupted data

Never remove the card when the indicator light is flashing – data is being transferred.
Always clear the card by formatting on the camera, not by deleting on the computer. Computer deletion leaves residual data on the card, but formatting removes it all. Remember to transfer photos before formatting.
Some cards are sold with image recovery software
Consider using several smaller capacity cards rather than one large one

Memory Card Reliability

Reliability is rated by the Mean Time Before Failure (MTBF) rate, based o the average failure period for a card type. For example, a card with 1,000,000 MTBF rate will last an average of 115 years.

How to Buy Memory Cards for a DSLR Camera

Before buying a memory card, it is very important to consider the specification of the camera, and also the photographic needs. For example, there is little point in buying a very high-speed card if the camera is not capable of taking advantage of the additional processing speed. Consider the kind of photography it will be used for. Professional photographers or serious amateurs are likely to have higher-specification equipment, and will probably need high-capacity cards, with relatively fast speeds.
Always be sure to buy from a reputable dealer, as a fake card could result in the loss of irreplaceable images.

How to Buy a Memory Card on eBay

To buy a memory card on eBay, go to the home page, and then All Categories.. Under the Cameras & Photography menu, select Camera & Photo Accessories, and then under Categories select Memory cards. Filters, such as New Condition and brand can then be applied.


Although it's important to consider storage capacity and speed when buying a memory card for a DSLR camera, neither factor affects the photo quality – this is determined by the camera settings chosen when the photos is taken. But it can make process of taking, storing and downloading photos much faster and easier.

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