Pixel Reference Table
SD cards are compact and lightweight, with fast transfer speeds, and are used by almost all consumer-grade digital cameras. The future development of this storage card is limitless. However, there are three concepts of SD/SDHC/SDXC in the market, which one is the most suitable for our cameras? Secure Digital, abbreviated as SD, stands for Secure Digital Memory Card, which is widely used in portable devices such as digital cameras, personal digital assistants, and multimedia players. SDHC and SDXC are new specifications for storage cards that emerged after SD, based on capacity and speed upgrades.
Specifications of SD Cards
SD cards offer different speeds, calculated based on the CD-ROM’s 150KB/s as 1x speed (noted as “1×”). Essentially, they can be up to 6 times faster than the standard CD-ROM transfer speed (900KB/s), while high-speed SD cards can transfer at 66× (9900KB/s = 9.66MB/s, labeled as 10MB/s) and 133× or higher speeds. Some digital cameras require high-speed SD cards for smoother video recording and faster continuous shooting. As of December 2005, most devices followed the SD card’s 1.01 specification, while devices with speeds up to 133× followed the 1.1 specification, with a maximum of 12.5MB/s.
In March 2006, the SDHC standard (SD 2.0) was released, redefining the speed specifications of SD cards into three classes: Class 2, 4, and 6, representing minimum write speeds of 2MB/s, 4MB/s, and 6MB/s, respectively. With advancements in technology, some manufacturers produced even faster SDHC cards. Manufacturers generally indicate speeds directly on these SD cards, such as R90/W60, representing read/write speeds of 90MB/s and 60MB/s, respectively. In SD 2.0, the standard defines ordinary and high-speed cards into four classes: Class 2, Class 4, Class 6, and Class 10.
In 2010, the new SD 3.0 was released, defining SDXC and UHS. The SD 3.0 specification is referred to as ultra-high-speed cards, and as of the second quarter of 2013, only UHS-Ⅰ cards were on the market. UHS-Ⅱ was released in the fourth quarter of 2012, but given the current technological development speed in 2014, UHS-Ⅰ is sufficient to last through 2014 and even longer. However, Toshiba’s early release of UHS-Ⅱ is currently the best among SD cards, initially usable only on the Fujifilm X-T1, with speeds approaching SSD. The speed levels of UHS-Ⅰ cards are divided into UHS-Class 0 and UHS-Class 1. The Class of UHS-Ⅰ differs from that of SD 2.0, with no explicit Class 0 cards, meaning they do not meet Class 1 standards. It is possible that in the future, all old Class standards will be classified as Class 0. Class 1 represents a maximum read speed of 104MB/s (with potential trends to surpass SSD), while the Class in SD 2.0 represents the minimum write speed range.
Recently, SanDisk officially launched the new Extreme Pro SDXC UHS-Ⅲ storage card, with a capacity of 512GB, currently the highest in the world, fully supporting 4K video, with a maximum transfer speed of 95MB/s, while the reading speed is currently unclear, likely around 300+. The SD card priced over 4000 yuan is still a possibility for some companies or affluent buyers.
This is the development history of SD, representing different capacity and speed standards. Although there are overlaps, the boundaries in these two aspects remain clear. Currently, SD card capacities include 8MB, 16MB, 32MB, 64MB, 128MB, 256MB, 512MB, 1GB, and 2GB; SDHC card capacities include 2GB, 4GB, 8GB, 16GB, and 32GB; SDXC card capacities include 32GB, 48GB, 64GB, 128GB, 256GB, and 512GB.
Keywords: Continuous Shooting
When it comes to continuous shooting, it mainly depends on the speed of the storage card, referring to the write speed here. For example, Sony’s A77 and A77Ⅱ are among the highest continuous shooting rate cameras, shooting 12 frames per second, with a JPEG image size of about 24MB, equating to approximately 288MB/second. At this speed, referring to the aforementioned, one would need to use UHS-Ⅱ or higher speed cards to fully utilize its continuous shooting capabilities. Theoretically, using storage cards below UHS-Ⅱ specifications would require significant camera buffering and waiting time to complete continuous shooting. If using RAW or simultaneously using JPEG + RAW, it would take even longer. To maximize the camera’s powerful continuous shooting function, it’s best to consider the latest defined SDXC, with speeds above UHS-Ⅰ.
If continuous shooting is not frequently used or if the camera’s continuous shooting speed is only 5 frames per second, using Class 10 and UHS-Ⅰ can generally fulfill most continuous shooting needs, with a minimum not lower than Class 6. If not using continuous shooting, it is recommended to use Class 4 speed SDHC or SDXC; older SD specifications should not be considered.
Keywords: Pixels
When discussing pixels, one must first set aside continuous shooting. The previous recommendation of using Class 4 speed or above is not unfounded. Currently, most cameras are in the tens of millions of pixels, with Nikon D800 having 36.3 million pixels. Assuming a 1:1 conversion, a single photo would require 36MB. Considering the camera’s high-speed cache, capturing a photo with up to 36.3 million pixels, Class 4 speed is still acceptable. However, it does not mean that recommending Class 4 storage cards is sufficient for Nikon D800 users, as continuous shooting must also be considered. In other words, when selecting an SD card, one can gauge the required speed based on the camera’s pixel count.
Among the most important aspects of pixels is capacity. It is recommended that cameras with around 20 million pixels be equipped with a 32GB capacity card, which can be either SDHC or SDXC; otherwise, it won’t be long before the card is full. For the Fujifilm X-T1, which has 16 million pixels and a continuous shooting speed of 8 frames per second, considering all factors, the UHS-Ⅰ speed of SDHC is more suitable.
Keywords: Video Recording
Currently, most digital cameras have video recording capabilities, and with the rise of 4K, many camera manufacturers have incorporated 4K video recording features into their cameras. Therefore, when purchasing storage, it’s advisable to pay special attention to video functionality. For video recording, a high-speed card or even an ultra-high-speed card is necessary. Generally, the minimum speed should be Class 10, as video recording is significantly influenced by the storage speed, bitrate, and shooting resolution. As previously mentioned, recording 4K resolution video requires speeds of UHS-Ⅰ or higher to support it. When using the Sony A7S for video recording, attempting to use an SDHC card resulted in stuttering during recording; switching to an SDXC card resolved the issue.
In summary, as photography enthusiasts, when purchasing storage cards, we must consider capacity to ensure we have enough space for our shots, and speed to allow us to maximize the performance of our “beloved camera.” In the future, when buying storage cards, opt for SDHC/SDXC specifications, with speeds at least Class 6 or above. For small digital cameras or those not frequently used for continuous shooting, a 16GB Class 4 storage card should suffice.
China Photography News Brand Creates Value
Postal Code: 1-126, available for subscription at post offices nationwide
Postal Service Customer Service: 11185
