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Originally published in my DIVER Magazine column Final Cut – March 2015

Choosing the Right Memory Card for Your CameraMemoryCards9512l

Digital cameras use a removable storage device in the form of a memory card in order to store your  video and photo files. When you tear open the box of  a new camera, you sometimes  need to temper your excitement. That new camera may not include a memory card, which means delayed gratification and yes, spending a few more dollars before you can use your new device.

Flash memory cards use solid-state technology, meaning that there are no moving parts inside the plastic case. Although all memory cards serve the same general purpose, there are proprietary formats and attributes you should understand before running off to the discount  store to buy the least expensive card you can find.

The good news for us divers is that memory cards are very durable. They are generally waterproof and can usually withstand immersion in salt and freshwater. As long as the card is fully dried and cleaned before use, it will operate as normal after it has been flooded underwater or been exposed to moisture in places such as a wet countertop, damp cupholder or in the rain. The same technology is very temperature resilient, shockproof, X-ray proof and basically able to be run over by a 5-ton delivery truck. (Not tested by this writer, but on my husband’s list.)

In general, Secure Digital and CompactFlash are the most common formats. Most new consumer cameras use the smaller SD format while larger, professional and prosumer cameras often use CompactFlash. A few cameras are able to facilitate  multiple formats and some utilize proprietary configurations such s Sony’s Memory Stick. The size and type of memory card is specified by the camera manufacturer, but beyond format, there is a literal minefield of features to consider when purchasing a card.


In the SD family of cards, you will find SD, SD High Capacity (SDHC) and the most recent Extended Capacity (SDXC) types. Most devices made in the last five years will likely accept SDHC and very new cameras will use SDXC. Cameras can use older cards, but older cameras may not be able to use newer formats. SD cards are also made in three physical sizes for different sized cameras – SD, miniSD and microSD.

Understanding Card Speed

All memory cards are marked with symbols and language that define their speed, which is further divided into write speed and read speed. Write speed is particularly critical for burst shooting and video applications, while  read speed is noticeable when downloading images to your computer.

Cards may be described with a multiplication factor that indicates read speed (200x, 300x, etc.). This is called the “Commercial X Rating.” A 200x rated card is equivalent to 200 times the speed of an original CD-ROM which ran at 150 KB/sec. Therefore a 200x card will read a 29.5 MB image file in one second (200 x 150 = 30,000/1016 = 29.528). More recently, the SD Association  devised a speed class rating which describes the minimum data transfer rate of SD/SDHC/SDXC cards. Class 4 cards will perform 4 MB/sec; Class 10 cards reach 10 MB/sec., and so on. This is important for video recording so that the card can keep up with  the data stream pouring out of the camera.

In a nutshell, purchase the fastest card you can afford.

A photographer may be happy with a Class 4 card, but a video shooter should look for a Class 6 card if their camera supports it. Read the manufacturer’s recommendations to be sure you are not overspending on something that will operate slower in an older camera. The capacity of the card is described in GB. Although you may be tempted to buy a large capacity, don’t use this as an excuse to retain two years worth of footage and photos before you download to a computer. Store only as much as you are willing to lose. Most cards are specified with a Mean Time Before Failure (MTBF) of over 100 years but occasional failures or physical loss are not unheard of.


Compact flash cards are rated with transfer speed which is the highest possible read speed, but bear in mind that the rating on the SD card indicates minimum write speed. When tested, many SDHC and SDXC cards tend to deliver 20-30 MB/sec (133-200x) and have potential write speeds of 80 MB/sec and are gaining speed all the time.

Maintaining Your Card

When you finish your day of underwater photography, take time to offload your photos to your computer or other device. Once you have completed this task, reformat the card in the camera to minimize errors and potentially increased speed. If you are using a GoPro or similar camera and don’t reformat, at least “empty the trash” on your computer to ensure availability of the full capacity of the card. Remember that formatting a card will irretrievably erase files, so ensure they are backed up first.

So, after the joy of unboxing a new camera, take a moment to decide which card will work best for you. Consult the instructional manual to ensure you are not purchasing more card than you can handle. Turn your focus to the capacity and speed that best fits the camera and your budget and stick to a known and reliable brand.

FAQ: Which card should you buy for a HERO4 GoPro?

SanDisk Extreme 32GB to 64GB microSDHC or SDXC or Lexar 32GB to 64GB 633x microSDHC or SDXC

How much shooting time?

Shooting any camera in 4K: A 64GB 100MB/sec card yields just under 30 minutes of shooting time

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