Buying a Good SD Card

They're all the same, right? Photo property of uk.hardware.info.

There are some technology items where it doesn't really matter which brand you're choosing or how much you're paying for it, you'll still end up with basically the same result. Take Monster HDMI cables for example: a 1m HDMI cable costs £18.99 on Amazon whereas the same, basic cable produced by IBRA costs only £5.45. Monster will try to sway you with their marketing talk of faster transfer speeds and rugged cable housing for added durability but if all you want to do is connect your Xbox One to the TV, every one of those cables will do the exact same, no difference in quality. SD cards though are a different story: it does matter how much you're spending.

Why does it matter?

I always used to think that SD cards were all pretty much the same and that spending more than was necessary for one's desired GB size was pointless. Until I did some testing. Recently, I purchased a PNY 32GB SDHC memory card. I picked this card primarily because it's made by PNY - SanDisk, Integral and PNY are arguably the three biggest players in the world of SD card manufacturing (in that descending order). I could have picked a smaller brand and gone cheaper but then I'd constantly be worrying about it becoming corrupted every time I booted up my camera. I had sort of gleaned some information online about SD card 'classes' and write speeds but my main priorities were brand and GB size.

Note the Class 10 symbol (the circular one). It's very important to identify which class your SD card is as that relates to minimum write speeds.

It was when I received my new card (in that frustrating plastic wrapping which is impossible to open) that I decided to do some testing to see if there was an actual, real-world difference and not some Monster-esque marketing nonsense. I could just tell you now that you should always aim to get a card with a higher class, and I will. If you want to save time, stop reading now and just remember 'Higher class = Better' (that number in the circle). If, however, you've got your nerd hat on and want to find out why a higher class is better (as well as read my ramblings), then thank you for continuing :)

Here were the two cards I tested:

Card 1: PNY SDHC 16GB Class 4 - Class 4 meaning a minimum write speed of 4 MB/s.

Card 2: PNY SDHC 32GB Class 10 - minimum write speed of 10 MB/s.

('Writing' is the transfer of information from the camera's sensor onto the card. An analogy would be an idea in your head [sensor] and then getting it down onto paper [SD card].)

Using the same camera, my Sony NEX 5R, I set it to shoot in 'speed priority continuous' mode. The camera stayed in the same location, and shot the same scene. The Sony 5R can capture photos at 10 fps (frames per second) so in theory, I should get 10 photos every second, as long as the camera and SD card are able to keep up and not have to buffer (that time when it has to slow down in order to write all those photos taken in quick succession onto the card).  

Testing, testing

Test 1: How fast to shoot 10 fps

PNY Class 4: 1.31 secs

PNY Class 10: 1.32 secs

Test 2: How fast to shoot 10 fps and then be ready for further user input (buffering time)

PNY Class 4: 9.73 secs

PNY Class 10: 5.54 secs

Test 3: How fast to shoot 20 photos continuously

PNY Class 4: 16.75 secs

PNY Class 10: 10.09 secs

Test 4: How fast to shoot 20 photos continuously and then be ready for further user input (buffer)

PNY Class 4: 26.20 secs

PNY Class 10: 16.29 secs

Speed is king/queen

Observation 1: Write speed has zero impact on camera's theoretical fps performance - both achieved 10 fps in almost the exact same time. 

However.

Observation 2: Higher write speed does have two large and positive effects.

1) You can take more pictures in a shorter amount of time - Test 3 ably demonstrates that: PNY Class 10 took nearly 6 seconds faster to shoot the next 11-20 photos continuously. 

2) Test 2 and 4 demonstrated that the wait time between taking those shots and then waiting for your camera to be responsive again (buffering time) was vastly reduced. In test 4, PNY Class 10 was nearly 10 seconds faster! It took PNY Class 10 the same amount of time to shoot 20 photos and then be ready again as it did for PNY Class 4 just to take those 20 photos to begin with!

You might be thinking, 'Okay, yes John, that's great, faster write speeds are helpful but when is it ever going to be likely that I will take more than 10 photos continuously?' That's a fair point but if you've ever shot a birthday party or sporting event or your sister doing a crazy mud, obstacle course (well done sis!), you'll know that speed is the key to capturing those candid, unscripted and miss-it-and-it's-gone moments.

By reducing the time to a) shoot more than 10 photos in quick succession and b) wait in-between buffering periods, the more time you'll get to spend on actually doing what is important: taking the photos in the first place (which your sister, brother, aunt, mum or friend can thank you for later).

One more thing

It took PNY Class 4 (minimum write speed of 4 MB/s) 10.00 seconds to import 10 RAW files into Adobe Lightroom. It took PNY Class 10 (minimum write speed of 10 MB/s) 6.34 seconds to import. My photo workflow is usually a lot greater than 10 photos (as I'm sure your workflow is) so the increased deficit in waiting time is compounded every 10 photos you import. 

The bottom line

To save you time and be in a better position to capture that moment, always aim for a SD card with a higher class. The more 'sophisticated' your camera is (and if you shoot in RAW), the more likely you'll need a higher class SD card.

I would recommend these cards for:

Compact cameras (Point and shoot): SanDisk Ultra 16GB SDHC Class 10

High-end compact, micro 4/3 or mirrorless cameras: SanDisk Extreme 32GB SDHC Class 10

High-end dSLR cameras (shooting HD/4K video): SanDisk Extreme Pro 64GB SDXC Class 10 UHS-U3

(Note: you may have noticed that all are Class 10 cards but show different xx MB/s rates. This relates to the bus speed - the frequency at which information is strobed in and out of the card. Faster rate = greater frequency. The bigger the file sizes you're working with, the greater the need for a faster bus speed.)

Integral and PNY equivalents are also fine from my past experience, you can't go wrong with any of those brands, just make sure you keep an eye out for that class number.

Thanks for staying with me, I hope this has been useful to you :)