Buying Guide: Memory Cards

This articles gives tips and advice on choosing and using flash memory cards. The internal memories in digicams can only store a few high-resolution image files, so a separate memory card is always required. New camera buyers should purchase at least a 1GB memory card with their camera. It’s a small investment; at the time of writing you could buy a 1GB CF or SD card for less than $30.

Buying a digital camera usually commits you to one type of memory card. For professional and semi-professional DSLRs, the choice is normally CompactFlash (CF), while entry-level DSLRs and compact digicams may be configured for SecureDigital (SD), Memory Stick (MS) or xD-Picture Card (xD), with SD being by far the most popular. A few cameras support two card types in dual slots, and one professional DSLR can take two CF cards.

When you use a high-capacity card in your camera, you are able to take all your photographs with the camera’s highest resolution and quality settings. It’s simple to down-size image files for emailing and posting on websites but, if you’ve shot at low resolution, your chance of making high-quality prints of your favourite shots will be compromised. Enlargements will be out of the question!

Note: Most cameras will accept cards with capacities up to 2GB but some are unable to use higher capacities. Many such models, along with older cameras, cannot work with the latest SHDC and UDMA cards. Always check your camera manual before buying a high-capacity card or one that offers faster data transfer speeds.

Card Capacities
How much memory do you need? A lot depends on the resolution of your camera’s sensor, the type of camera you use and whether you shoot JPEG or Raw image files (or both together). The table below shows the approximate number of pictures you can store on a range of memory card capacities for compact digicams of different resolution levels. The figures provided are based on JPEG images taken at the highest resolution and quality settings with typical compression levels.

The actual number of pictures that can be stored on a card will depend on the camera model and how much the JPEG files are compressed. Compression levels can vary greatly from one model to another, although advanced digicams usually support lower compression rates than point-and-shoot models. Details of JPEG compression levels and the number of files per card capacity for specific cameras should be provided in each camera’s manual.

Photographers who use DSLR cameras will find they need higher storage capacity than digicam users. Not only are JPEG compression levels lower than for digicams but image files will be substantially larger if they shoot Raw files (or Raw+JPEG). Compression ratios vary for Raw files, depending on whether and by how much the files are compressed, although all manufacturers provide lossless compression. In current DLSR cameras, 10-megapixel Raw files can range in size from 17.66MB to 9.8MB.

If your camera has a TIFF capture setting you’ll need even more memory capacity to take advantage of this file format. TIFF files, which are usually uncompressed, are approximately three times the resolution of the camera’s sensor in size (eg, around 30MB for a TIFF file from a 10-megapixel camera).

Video Requirements
Digicam users who wish to shoot video need much more memory than is required for shooting stills. We recommend at least 4GB, which is the limit most camera manufacturers put on video capacity. The compression ratio and file format used by the camera for video recording will dictate the size of the video files and how much video you can store. The table below shows typical video recording times for three different video formats with three card capacities.

Card Care
Flash memory is very robust. According to the CompactFlash association, as long as cards are adequately cared for, a properly-manufactured CF card could be expected to provide more than 100 years of normal usage with no loss of data. Other types of memory cards should be just as durable.

The following tips will help you to ensure your cards will provide reliable service:

1. Keep cards in dust- and water-proof cases while they are not in use.

2. Format each card in your camera before you use it, making sure you have transferred any data it contained to an archive folder.

3. Don’t open the camera’s card compartment while the files are being written; it will almost certainly cause shots to be lost.

4. Always carry at least one back-up card in case you run out of memory on a shoot.

Card Speeds
Regardless of the capabilities of the memory card you use, data transfer rates are primarily dictated by the camera’s internal processing system. There is little point in paying more for a fast card unless your camera is able to take advantage of it. Fast cards can be advantageous for shooting action, when the continuous shooting mode is used. They can also be worthwhile for video capture. For normal picture-taking, they offer minimal benefits over standard-speed cards.

Photo Review has recently tested five CompactFlash cards in several of the latest DSLR cameras we have reviewed. Each card was formatted in the camera, which was set to the manufacturer’s default processing settings. Our test target, which contained a moderately high level of detail, was evenly lit and the camera’s batteries were fully charged. Bursts of shots were taken using the fastest burst speed available in each format and we timed how long it took to empty the buffer memory. Timing started when the camera’s card status light went on and ended when it went off.

Testing involved three cycles of exposures, the first using JPEG at top resolution and quality, the second using Raw format and involving simultaneous capture of Raw and JPEG files. These cycles were repeated three times and the results averaged. The results are shown in the tables below.

Canon EOS 40D

Canon EOS 400D

Nikon D300

Olympus E-3

Sony DSLR-A700

Sony DSLR-A100

Note: Our test results should be used as guidelines only as write speeds depend more on the camera’s ability to process data than on the actual speed of the card itself. Raw files are normally transferred faster than JPEGs because they require less processing. Write speeds can also be slower in higher capacity cards than lower capacities – even with identically branded cards.
Beware of Counterfeit Cards
Some memory cards that are sold online or offered through discount outlets may appear to be from a leading manufacturer but beware: they lack the warranties of the genuine products. Check the Photo Review website before buying memory cards for up-to-date prices on different card types and capacities. Examine card labels very carefully and only buy from reputable re-sellers. If the deal seems too good to be true it probably is.

Further Links:

Lexar Media: http://www.lexar.com/au/

Verbatim: http://www.verbatim.com.au/products/digital_media.cfm