Tuesday, April 20, 2010
Hi-Tech Studio: Memory Requirements
CompactFlash remains the mainstay memory card for professional DSLRs. We look at speed ratings, HD video requirements and some of the current generation of pro cards.
CompactFlash just keeps getting better and better. And where digital SLR cameras are concerned, better means faster data-transfer speeds and higher capacities. Celebrating its Sweet 16th birthday this year, CF delivers specifications that allow professional cameras—and professional photographers—to perform at their maximum capacity.
High data-transfer speed, also known as read/write speed, allows cameras to rapidly write buffered images to the CF card for permanent storage—which means you can shoot as fast as the camera was designed to shoot without a bottleneck at the storage end of the pipeline. Conversely, when it’s time to download, you can transfer images from the CF card to your computer’s hard drive in less time. When cards maxed out in the 2 to 4 GB range, that didn’t matter much. But now that 16 GB and 32 GB cards are quite common, download speed has become significant.
Most manufacturers rate their cards based on the original read/write speed of a CD-ROM, which zipped data along at 0.15 MB/s. That baseline rate is “x,” and card speeds are expressed as multiples of that speed. For example, 60x represents a sustained write/read speed of 9 MB/s (multiply 60 x 0.15 MB/s). This is the potential speed, not necessarily reality. And in some cases, it refers to top speed, not sustained speed. Also, the transfer speed rating isn’t the only factor that affects performance. Matching a high-speed card reader to high-speed cards is important if you hope to attain peak throughput.
Speed and capacity are particularly important for the current generation of multi-megapixel cameras that capture HD video in addition to large RAW files. In the SDHC card world (see sidebar), the minimum specification for satisfactory video capture is speed class 4, which equates to a 4 MB/s sustained read/write speed. This actually is a very low threshold. Nearly all CF cards currently available from name-brand manufacturers can handle HD video. But you always should opt for the fastest cards you can afford in order to ensure you’re enjoying the full speed potential when it comes to video capture, burst shooting and downloading.
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