On initial glance from the title, one might think this blog is segueing into a dialog from the Top Shot show over on the History Channel (very cool show btw), but I’m actually referring to the notion of speed often associated with shooting digital. Sports shooters, action shooters and the like often will get the fastest cameras, the fastest cards they can get, with the fastest processors, and go to all sorts of degrees to eliminate bottlenecks in their capacity to shoot fast and on the go. To an extent, their efforts are justified, but how fast does your card need to be?
As you may recall on Monday, I talked about how the real meaning of memory in media cards. We talked about Megapixels and Megabytes, and I gave some real world number ranges for what you could expect a media card to handle. So, today, we’re going to follow up on that topic of discussion and take a look at speed ratings for cards. As always, there’s a lot more to it than meets the eye, primarily because there are lots of numbers bandied about when speaking about card transfer rates. Before we wade hip dip into this, one brief note here is to give serious props to Rob Galbraith for compiling a pretty extensive database on his website of data transfer rates for a whole slew of cards with a whole slew of cameras. If you really want to dig into the minutia of how fast cards really are, be sure to check it out! Just one note though, that this database has not been updated since 2008 so cameras made since then will not be found with any reliable information.
With that in mind, today it’s probably more helpful to walk through the various points that can contribute to data transfer rates for cards. The natural first stopping point is in the camera itself, in what is commonly known as fps, or “Frames Per Second”.
Frames Per Second
Quite simply this refers to the number of actuations a given shutter in a camera can cycle through in exactly one second. As indicated above, the abbreviation for this is typically fps, and is easily culled from the spec sheet for pretty much any camera on the market today. For those of you that want to see a compilation though, here you are (I should note that I grabbed all this data from the vendor websites on claimed fps for the highest resolution image settings. If you set your file size to sRaw, or jpg and add compression, your max frame rate may increase…:
|Canon||1D Mark IV||10||Nikon||D3S||9|
|Canon||1D Mark III||10||Nikon||D300S||8|
|Canon||1Ds Mark III||5.0||Nikon||D90||4.5|
|Canon||5D Mark II||3.9||Nikon||D5100||4|
The bottom line here though is that with most DSLR’s on the market, if you expect more than 10 fps, that’s probably not going to happen (assuming also you are shooting continuous and on the highest resolution setting.)
So, even the camera you have can cause bottlenecks in write speeds…if your camera can’t write data that fast, it really doesn’t matter how fast your card can write data if it doesn’t have the data to write. Now granted, each camera will have different MP counts so the Canon 5D (for instance) will of course have a slower fps rate because it’s a larger file, and it’s a full frame camera, so will naturally be slower than the 7D by comparison simply because it has to be. So what we really need to be measuring is the amount of data that is being transferred per second (see now why I did that article first? 🙂 ) So, we’ve reached the second point of bottleneck now in talking about transfer speeds and that’s the buffer.
The best analogy I have is that the buffer in a camera is very much like the RAM in your computer. It’s a sort of staging area, where data is stored before it gets actually sent to the processor and then saved to the card. Without the buffer in place, fps rates would drop dramatically because there would be no place for the camera to temporarily hold data before writing. The buffer is what allows you to keep shooting. So, this brings up two important questions:
1. How can you increase the buffer? (You can’t really…)
2. How can I tell how much of a buffer my camera has? (As of this writing, I am not sure if this metric is reported consistently by vendors, except when reviewers say “an increased buffer size improves performance”…which is still relatively meaningless.)
Since it’s not something we can really measure, nor change without buying into a whole new camera, here it’s just sufficient to say that this is the second bottleneck point, and is usually where you will run into moments of pause. Why? Because cards are usually transferring data that fills up the buffer, and at that point the camera can’t take in any more data. When this happens your camera won’t let you take any pictures.
The other factor that comes in to play though ties more to the card itself and not the camera, which is the speed factor.
Speed Class Rating
Media card vendors like Lexar, Sandisk and others like to use terms to define their speed. Catch words like Extreme, Pro, Extreme Pro, 300x, 600X and all sorts of fancy jargon is used for marketing purposes. Notice the various cards on the market – the more buzz words, usually the faster the transfer rate claim, and of course, the more expensive the card! 🙂
So, rather than pour over all the various vendor semantics, I figured it’d probably be better to stay on what is a more neutral metric – speed class ratings. While we could also introduce variances between the CF and the SD format in terms of write speeds, since most devices are moving to the SD format and it’s smaller cousins (mini SD and Micro SD), these are likely the ones we’ll see more often in the future, so the speed class ratings here are most relevant.
To that end, there are 5 different ratings or grades given to SD cards. These are 2, 4, 6, 10, and 1 respectively. The last rating (1) is reserved for the SDHC and SDXC card types, and has a special designation as UHS, for Ultra High Speed…while the lower ratings all have transfer rates classified as normal and high speed. A full chart is viewable on it here. In a nutshell, the higher the number, the faster the card can transfer data, so keep that in mind as you shop for media. The ultimate barometer really though is not how fast you need to capture, but more what you need to capture, and as the chart indicates, video needs faster transfer rates than stills, so naturally the higher ratings are intended primarily for videographers.
If you really wanna geek out on data transfer rates, a better place to go for that is the Rob Galbraith database I mentioned upthread. Again, it’s not been updated since 2008, but the general trends are probably consistent with the current market of vendors we have to choose from.
One final note on data transfer rates…card technologies have changed substantially in recent years, enough that there are now cards referred to as UDMA cards. While the current generations of cameras from both Canon and Nikon support this mode of reading and writing data to media cards, older cards may not and will read the card at the slower rate. So, if you have an older camera, you may want to check for UDMA compatibility before getting a newer UDMA style card.
So, what’s the takeaway from all this? Hopefully three things:
1. Transfer Speeds are not just a function of your media card, fps rates and buffer rates in cameras are factors too.
2. Paying more for a faster media card might not be needed if you are not shooting video.
3. If you are shooting video, or need the extra oompfh of speedy cards, make sure you are using the right speed class, and with the best camera you can. As the old adage says: it’s a poor craftsman that blames his tools…
Happy shooting and we’ll see you tomorrow to wrap our discussion of Media Cards with a look at the various vendors!