What to look for in an SD card

ALMOST ALL DIGITAL CAMERAS USE THIS ONE MEMORY CARD TYPE, SO WHY ARE THERE SO MANY VARIATIONS? WE CUT THROUGH THE JARGON TO EXPLAIN ALL.

ROCKET SCIENCE AND brain surgery are reckoned to be the two most complex disciplines imaginable – but we’d like to add choosing an SD memory card to that list. In principle, it should be quite simple. They’re all the same size, so it’s just a case of working out how much capacity you need and how much you want to pay, right?

Not exactly – because as anyone who’s ever gone shopping for an SD card will know, there is an incredibly confusing choice of speeds, capacities, class ratings and standards to navigate. The best card for stills photography may not be the best for video, and you could easily end up spending too much money on a card with higher performance than you need.

So here’s our simple guide to making sense of all the SD card types currently on sale, their pros and cons and their associated jargon.

SD VS SDHC VS SDXC

The original SD Card format was a pretty feeble thing, with a maximum capacity of just 2GB and transfer speeds that were tolerable for the cameras of the time, but no good for today’s models. SDHC (High-Capacity) cards are now the basic norm, offering capacities up to 32GB and enough speed for Full HD video (depending on their Class rating). If you want higher capacities and 4K video recording, you need an SDXC (eXtendedCapacity) card.

SD AND MICROSD

There are three sizes of SD card, but only two in common use. Regular cameras use the standard SD Card size. There is a miniSD format, but in practice the only other common size is the microSD format, used in action cams and 360 cameras.

CAPACITY

If you shoot JPEGs, practically any card will do: it’s quite hard to find cards smaller than 8GB these days. If you prefer to shoot raw files, 32GB is a sensible minimum.

MAXIMUM SPEED

Memory card makers traditionally quote their card’s maximum data transfer speed. It’s a reasonable guide to the card’s speed for stills photographers, though read and write speeds are different and makers often quote the faster ‘read’ speeds. Maximum speeds may be quoted in MBps or as an ‘x’ number based on the old CD-ROM speed of 150KBps. 50MBps is tolerable; 300MBps is very good.

VIDEO CLASS RATINGS

Maximum speed doesn’t tell the whole story. If you shoot video, it’s the minimum sustained speed that counts. Slower cards have Class ratings – Class 2 is feeble and only good for standarddefinition video; Class 4 is OK for standard (720p) HD video; and for Full HD you’ll need Class 6 or Class 10. Class 10 cards overlap with the newer UHS Class I (U1) rating, but there’s a higher UHS Class 3 (U3) rating for 4K video. For 4K, this is being superseded by new V30, V60 and V90 standards.

UHS-I AND UHS-II

UHS-I cards look like regular SD cards, but offer higher transfer speeds (50-140MBps), while UHS-II cards have a second row of contacts on the back and offer much higher transfer speeds (156-312MBps). This is more important for videographers than stills photographers.

COMPATIBILITY

Unless the maker has provided a firmware update, you may find your elderly DSLR can only use the old SD cards available at the time and not newer SDHC or SDXC types.

THE BEST CARD FOR STILLS PHOTOGRAPHY MAY NOT BE THE BEST FOR VIDEO, AND YOU COULD EASILY END UP SPENDING TOO MUCH MONEY ON A CARD WITH HIGHER PERFORMANCE THAN YOU NEED.