Understanding DSLR Memory Cards


CF cards have been the traditional memory format for DSLRs. However, the use of SD cards is becoming more common. Both CF and SD cards are solid state memory devices that retain their information even without power. Check your camera manual to see what types of card your camera accepts. It may even accept both SD and CF cards.


What to look for in a memory card?
The most important aspects to look for in a memory card are size (how much data it can hold) and read/write speeds.


CF Cards
cfCF cards stand for Compact Flash and come in two different thicknesses:
1. Type I (3.3 mm thick)
2. Type II (5 mm thick)

Nowadays, CF cards are primarily Type I cards. Some card manufacturers describe their read/write speeds with an x (for example 133x) which is the card’s performance in relation to that of a CD. If not listed on the CF card packaging, it’s helpful to go to the manufacturer’s website to refer to what data transfer speed that actually means. CF cards are more expensive than SD cards but CF cards at their max speeds are slightly faster than SD cards.


SD Cards
sd cardsSD cards are vital components of DSLR video. SD stands for Secure Digital (not to be confused with SanDisk, which is a brand of SD card). SD cards are memory cards that store your pictures and videos. SD cards are quite popular. However, different camera models may require different type of memory cards, such as a CF cards, so check your camera manual before you start purchasing SD cards.


What does SDSC, SDHC, SDXC mean?

There are 3 categories of SD cards based on their capacity/storage size:

SDSC (Standard Capacity) 1 MB to 2 GB, some 4 GB available
SDHC (High Capacity) 4 GB to 32 GB
SDXC (eXtended Capacity) 32 GB to 2 TB!


What size card do I need?
The size required for your video files depends on a number of factors such as the video resolution, compression format, or Picture Style used. Your camera manual should provide a general recommendation for how many photos/videos can be stored per card size.


What do the different classes mean?
In addition to storage capacity, SD cards vary in their read and write speeds (how fast data can be written to and read from the card). The different classes help to identify the speed of the card. UHS stands for Ultra-High Speed and is available on some SDHC and SDXC cards. Check your camera manual to determine if UHS cards are compatible with your camera body.

Class Minimum Speed Performance
2 2 MB/sec+
4 4 MB/sec+
6 6 MB/sec+
10 10 MB/sec+
UHS-1 15 MB/sec+

Note that the listed speeds in the chart above are the minimum speed performances. Class performance can vary among brands. One brand’s class 6 can be faster than another brand’s class 10, so check the actual speed specifications on the card’s packaging.

Video recording requires high sustained write speeds so it’s not recommended to use anything below a class 6 card. A too slow card will only be able to record for a short period of time before producing an error message and stopping recording. I like to envision this concept with the I Love Lucy chocolate packing scene, where Lucy must wrap chocolates as they come down a conveyor belt:

Think of the chocolate as information coming from your camera, and Lucy as the SD card processing the information. At first Lucy managed to wrap a few chocolates just fine, but as more and more of the chocolate came quickly down the conveyor belt she wasn’t able to keep up. Similarly, if your SD card doesn’t have a fast enough write speed, it wont be able to process the information fast enough and there will be an information overload, the card will error out, and recording will be stopped.


What kind of SD card do I need?
Now that you know how to read the specifications of an SD card, it’s time to figure out what your camera is compatible with. To find this out, check your camera’s manual.


Which brand of cards should I buy and does it matter?
Different brands offer different levels of reliability. Further, different brands have different performances among the classes so branding does matter. Lexar and SanDisk are the most trusted SD card brands. However, be wary of knock offs that may be labeled as SanDisk or Lexar but instead are cheap ripoffs. If the price seems too good to be true, it probably is. So make sure you buy from a reputable dealer like B&H Photo or Amazon (from Amazon itself and not a third party vendor).


eyefiEye-Fi cards
Another brand of SD cards is the Eye-Fi card. What made these cards unique is that they are SDHC cards that have built-in WiFi which allows you to automatically upload photos & videos wirelessly to your computer, tablet, or smart phone. It’s advertised as having endless memory because as you take the pictures, it can automatically free up space on the card once the media is safely delivered wirelessly. No more having to connect cables or worry about damaging the SD card connectors when you pull it in/out of the camera or card reader. It looks like other SD card brands are also catching up. Transcend is also offering their version of a Wi-Fi SD card.


How long do SD cards last?
Of course there is no definite answer as to how long an SD card will last, and it is subjective based on a number of items such as the brand of card, how often it is used, what physical conditions it’s placed in, etc. Occasionally, the card might even be dead right out of the package. So always make sure to test your card before shooting for real.

Generally, the SD card connectors are said to be the weakest part of the card and are estimated to withstand 10,000 insertions/removals into and out of a camera or card reader. Additionally, the individual memory blocks in standard memory cards only have a limited amount of times they can be written to before it fails. It’s estimated that the sectors can last at least 100,000 program/erase cycles (number of times data is written to the card). SD card manufacturers have implemented wear leveling algorithms so that data is put on different sectors of the card to balance the “wear” across the memory card. There are also algorithms to automatically map out memory sectors that fail. Even with these advances, the general consensus seems to be that after 2 years it’d be a good idea to stop using that card in regular rotation as it is more likely to fail.

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