SD Cards Quick question.

[Mark500D]

I have a Class 4 SD Card in my 500D I know I need faster, but I don't want to waste money. Is there a need for a class 10 card. My manual say class 6 or higher would be best. (I don't think class 10s where out when my camera came out. (I could be wrong)) When I bought my card and camera back in 2011 I didn't know about card speeds. So should I get a class 10 card? Also are there any cards I should avoid?

[Hereford_EOS]

Re: SD Cards Quick question.

SD cards are quite cheap, you can get a 16Gb class 10 for less than £14.00 from Amazon

[DrJon]

Re: SD Cards Quick question.

Class 10 should be a bit faster as it means the card can write the data into its flash at a higher rate (provided the camera can move it to the card fast enough, I would assume the 500D is new enough to take advantage of Class 10). However this mainly affects how fast the camera buffer will clear so is only an issue if you shoot a lot of stuff in a short period of time. Note the 500D supports SDHC cards but not SDXC cards (see below). So my answer is yes, I'd say get a class 10 card as there is barely any price difference these days and it should help out a bit. I'd also go for a well-known manufacturer as a card going wonky on you is much more serious than a few pounds price difference (e.g. Sandisk, Lexar, Integral, Transcend).

I believe a 500D Raw file is about 22MB and a JPEG 5MB, 3MB, etc based on your chosen compression amount. Hence every push of the shutter could add 27MB to a card, shoot five shots and it's 135MB. A class 10 card could write that in 13 seconds, a Class 6 in 22 secs. If you fill the card you can't change cards until it's done without losing data. If you fill the buffer in the camera it will take less than 3 secs before you can shoot again with Class 10 card or 4.5 secs with Class 6. That's actually a while (look at a second hand). (I'm assuming a 500D just needs to empty a shots worth of buffer before shooting again, not the whole buffer, this is true of most recent cameras.)

BTW the "Class X" numbering is a beginning to get irrelevant as there are many other criteria affecting speed and no Class faster than 10 has been defined, even after a big bunch of years (and card speed increases). The number is the guaranteed performance in MB/s, so a Class 10 card is guaranteed to exceed 10MB/s for read AND write. However you can buy 45MB/s and 95MB/s ones (I have both, plus other speeds), but they are still called Class 10 as the scheme doesn't go any higher. These fast cards are handy as they improve buffer flushing if you are shooting a lot (especially Raw) and improve transfer time to the computer. Also if your camera supports shooting stills during video recording you should get a lower (or no) interruption in the video.

Also note when working out video speeds the data rate is given in Mb/s so divide by 8 for MB/s. Hence my GH3 camera will record video up to 72Mb/s but that would still be okay with a class 10 card, as that's 80Mb/s. A number less than 10 wouldn't be any good. For stills it's just down to how fast the buffer in the camera clears (plus how big the buffer is) so speed isn't as critical.

Another issue with fast cards is whether the camera supports them, no point buying a 95MB/s card if the camera tops out at 20MB/s (well, except for card reader performance, but...).

There are also many handy tacked-on additions to the SD spec...
SD - the original, goes up to 4GB (although I think only one company makes 4GB standard SD cards, the rest stopped at 2GB, I use them in my car as the audio player only supports SD and it gets me more music).
SDHC - High Capacity version, most cards over 2GB are this, some old cameras won't support it, goes up to 32GB.
SDXC - eXtended Capacity, goes to huge sizes, athough does mean don't buy a 64/128GB card unless your camera supports SDXC. (BTW 16GB and 32GB SDXC cards do exist but are usually SDHC compatible too.)

On the speed front as I said they stopped at Class 10 but then they added U ratings, which are UHS-I and UHS-II, plus UHS104 which is a go-faster version of UHS-I. Basically these run the serial bus the card transfers data over at a higher rate and so allow faster data transfer, UHS-II allows up to over 300MB/s (theoretically, UHS-I is 50MB/s) but cards using that would still be Class-10 as that's the fastest Class.

Also different manufacturers measure the "headline" MB/s speed they quote differently as it isn't covered by the standard, so Lexar are guaranteed minimum read speed (but wouldn't write speed have been nicer for camera use) and Sandisk are "up to". Hence is a Sandisk 95MB/s card better/worse than a Lexar 90MB/s - who knows (plus it might relate to how the camera talks to it).

Hence if you look at the picture here:

http://www.amazon.co.uk/Lexar-Professional-Class-UHS-1-Memory/dp/B006YAOS4E

It's an SDXC card, which it must be as it's 64GB so will only work in cameras with SDXC support. Speed is Class 10 but Lexar guarantee you can read from it at least 90MB/s which they've written on the card as a multiple of the old 1x CD-ROM speed (150kB/s) to confuse people or just look impressive (I don't think I ever owned a CD data drive that slow). It says it's UHS-I (shown as an extra I after SDXC) but actually it's UHS-104 as UHS-I isn't fast enough to get 90MB/s. However it will only be that fast if your camera can make the 208MHz clock UHS-104 supports, otherwise the speed will be about halved using the 100MHz clock (50MB/s max) of UHS-I (it will still work though). It's also UHS speed class 1, which is 10MB/s, and shown as a U with a 1 inside it (so obviously nothing to do with UHS-I, err, handy that, not) and also somewhat pointless IMHO.

Here's a Sandisk one:

http://www.amazon.co.uk/SanDisk-64GB-Extreme-Video-UHS-I/dp/B0070WU51U

Most of the writing should be clear now, they just use MB/s instead of x.

Do note the speed is critically a function of the Camera too, plus you care more about write speed which no-one quotes. Rob Galbraith used to keep a database of card speed in assorted cameras, which could be illuminating, but he's had a job change and isn't keeping it up.

Hope that isn't too confusing.

John

[DeeGee]

Re: SD Cards Quick question.

I have a class 10 in my 500D, whether the camera uses it to its full potential is another matter.

I figured that when I was rapid firing (A rare event) then it would come in handy. My other thinking was that it might be better put together with a little bit more care (slewed thinking I know:smile:)

The main reason however is I had a voucher. :smile:

[S_J_P]

Re: SD Cards Quick question.

Thanks for the comprehensive write-up DrJon, that's cleared up a lot of uncertainties I had!

I did a series of tests using various classes of card in my 60D a year or so ago, and was surprised by the results. The number of consecutive shots I could take, and the frame-rate after the buffer filled remained relatively constant regardless of card speed, but the time to clear the buffer was significantly reduced with the faster cards.

[Mark500D]

Re: SD Cards Quick question.

The reason for the Class 10 card (Taking into account DrJon's comments) I went a the airport a few days ago, and took load of photos, a lot on the multi-shot setting. I felt had I had a faster card I could have got more off. lol.