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Camera Card Speeds

The book I bought to explain my new camera recommends that I use a UHS class 3 (UHS-3) SDHX card. When I shop online, I find cards described as "Class 10 UHS I, U3 performance." Is that the same thing?

Posted by
606 posts

UHS 1 writes at 10MB/sec. UHS 3 writes at 30MB/sec.

You will need the faster write speed if you are shooting high-res 4K video.

Posted by
5017 posts

Depends on your camera, and what you’ll be doing with it. For still photos (not video), basic one-off travel snapshots, carefully composed landscapes, basics, you do not need a fast card. If you are more of the “run and gun” style (shooting lots of frames in rapid succession), your camera’s procesor might generate shots faster than they can be written to a slow card.

You may need faster cards if you do some of the following (especially if you do more than one of them at the same time):

  • if you are shooting in Burst Mode
  • if you are shooting large, high resolution photos in both RAW and JPG at the same time

If you have no idea what these things are then you probably will never need a very fast card.

If you will be shooting wildlife (birds in flight, an especially tricky challenge) or sports, then the above would apply.

My big camera is capable of capturing images at a truly breathtaking rate. I always shoot in RAW+JPG, and occasionally shoot burst mode for wild animals in movement (including birds). Do that for more than a few seconds, and even with the fastest (stunningly expensive) memory cards, the card can’t keep up and it buffers - do that enough in a short period of time, the buffer can become full, then it can’t/won’t take any more shots until the buffer is written. Doesn’t happen often, and it’s my own fault when it does (the fix is to restrain the photographer’s shutter finger - keep bursts short, or reduce the burst rate).

If the above is all just meaningless technobabble to you, stop worrying about card speeds.

Tip: test all your cards several days before you start packing for your trip. If you got the wrong kind (or if one goes bad) you’ll have time to return/replace it before heading off. Don’t waste prescious time on your trip shopping for camera stuff in a foreign land.

Happy shooting!

Posted by
486 posts

Thank you for these comments. However, my basic question remains. How do I make sure that the card I am buying has the UHS 3 speed class? The product descriptions I see online don't describe the cards in the way I expect.

Posted by
5448 posts

First do you mean SDHC (high capacity) or SDXC (extra high)?

Speed is marked with a number in an open circle like a "C" 2 through 10 for high capacity or single digit number in a square "U" for the ultra high capacity category. That means you are looking or a 10 in a "C" high capacity or a 1 in a "U" ultra high capacity.

Speed Class, UHS Speed Class* and Video Speed Class*** symbols with
a number indicate minimum writing speed. This is mainly useful for
camcorders, video recorders and other devices with video recording

A 3 in a "U" mark would be a U3 speed class card.
Something like:

While this card has been designed for cameras that are UHS-I / V30 /
U3 compatible, it may be used in devices that do not support UHS-I /
V30 / U3. However, bear in mind that this card will then default to
your device's speed class and bus rating, such as UHS-I and U1, which
supports minimum write speeds of 10 MB/s, or Class 10, which also
supports minimum write speeds of 10 MB/s.