memory card speeds

[calexe]

Hello friends,

Does anybody of you owe a 7D with a 90MB/s (600x) CF card? If yes, could she/he be so kind to measure the time the buffer gets empty after a burst at 8fps recording RAW images?

Reason: I need to make a decision wether it makes sense to buy 90MB/s cards; or maybe 60MB/s cards are fast enogh? My application: wildlife, sports, action.

How to do it:
Put your lens in manual focus mode. Choose program M on camera, some tiny shutter speed (say <1/1000s), burst speed on H (8fps), recording RAW images of largest resolution. Fully press shutter button. You will hear high rate shutter noise until buffer gets full, then burst speed will lower down. At this moment, say t1, release the shutter button and watch the red LED beneath the big control dial, which is on. When it goes off, say t2, then the buffer is empty. Finaly, the time the 7D buffer gets empty is t = t2 - t1.

Normaly CF with higher speed should allow the buffer to be ready earlier for next burst, but this depends also on the write speed of the controller embedded in the 7D, and I did not find a specification for its speed. On the other hand, different card manufacturers indicate some speed on the cards (xxMB/s, nnnx, class xx), but these indications may not be always reliable. E.g.: 60MB/s is actually the read speed of the card. Write speed is lower, and some manufacturers "forget" to specify it.

Some results from me:
- Sandisk, 16GB, marked 60MB/s (400x): t = cca. 8s
- Sandisk, 4GB, marked 30MB/s (200x): t = cca. 18s

Thanks in advance.

[Armistice]

Hi.

I have a problem with my EOS 500D concerning writing speed.

Since the camera features full HD video capture, I have a class 6 4GB card for a start.
Now the manual says full HD needs 330 MB/min that's roughly 5 MB/s. Class 6 (6MB/s) should do this.
However, whenever I use fullHD video, it starts buffering after roughly 10 to 15 secs of video, stoping the record roughly after.

Now did I get framed with the SD card? Does anyone else have experience with this?

[rick55]

Hi.

I have a problem with my EOS 500D concerning writing speed.

Since the camera features full HD video capture, I have a class 6 4GB card for a start.
Now the manual says full HD needs 330 MB/min that's roughly 5 MB/s. Class 6 (6MB/s) should do this.
However, whenever I use fullHD video, it starts buffering after roughly 10 to 15 secs of video, stoping the record roughly after.

Now did I get framed with the SD card? Does anyone else have experience with this?

Hi, Armistice, and welcome to CiC! Do you prefer "Armistice," or is there another name we can use?

I also have a 500D, but I've only used the video feature once, and I have a fast SD card, so I haven't experienced the problem.

But in reading the manual, I note a couple of things. I believe the specs you mention (330MB/min), on page 214, are capacity rather than transfer rate. It's telling you how much space a movie of a particular type will use on your card. Then there's a note on page 121, at the beginning of the movie shooting section, that says you need to use a class 6 to record movies at all: you're unlikely to be able to record or playback with a slower card. The notes on page 127, talking about how the "buffer filling" indicator may or may not appear based on whether you have a slow or fast card don't mention any specific speed for slow or fast, but if class 6 is the minimum speed to record a movie, I'd expect that it's what they mean by "slow."

It would certainly be nice if they were more specific about what they mean by fast and slow, so you could get a card to do what you want. I can try a longer movie with my camera, but the only SD cards I have are class 10. I'll be glad to do a test, if you like.

Cheers,
Rick

[Colin Southern]

Hi.

I have a problem with my EOS 500D concerning writing speed.

Since the camera features full HD video capture, I have a class 6 4GB card for a start.
Now the manual says full HD needs 330 MB/min that's roughly 5 MB/s. Class 6 (6MB/s) should do this.
However, whenever I use fullHD video, it starts buffering after roughly 10 to 15 secs of video, stoping the record roughly after.

Now did I get framed with the SD card? Does anyone else have experience with this?

Until recently, Class 6 was the highest official class - so something that was 6mb/s was class 6 and something that was 20 mb/s was also only (officially) class 6 - so depending on the manufacturers, you could have two class 6 cards with dramatically different performance. (I found this out "by accident" when I bought a bargain 16GB Adata card for the 2nd slot in my 1Ds3 ... it took about 5 seconds per image to write to it -- I upgraded to recently to a 32GB Sandisk Extreme III card and it's about 3 times as fast).

So my thought is that you probably have a budget / generic low performance card (or a counterfeit of a named brand like Sandisk). I'd be 99.9% sure that if you bought something like a (genuine) Sandisk Extreme III card you'll be away laughing.

[Armistice]

Thanks for the quick answer!

The card I have is a no-name card. It's class 6.
I went to a photo-equip shop and explained them my problem, they couldn't help me but they let me try a different SD card(Panasonic it was) and it was only a class 4 card.
Things worked like a charm.

Now the "classes" as i read in the wiki are only a minimum writing speed.

I suppose the brand class 4 was faster than the noname class 6. I'll go buy a branded class 10 card.


Wiki states that class 6 is 6 Megabyte(48 Mbit) per Second, most cards I see in the shops have 20 MB/s aka double the speed of a Class 10 card.
I'll make sure to try them out next time before I buy them.

You're probably right Colin.
Cheers!

[Colin Southern]

Thanks for the quick answer!

No worries

If in doubt, stick with genuine Sandisk!