What is the speed of the bus from the buffer to the mem card on a 40D?

Maybe I just missed it, but I looked through the specifications in the 40D manual and didn't find anything about the speed of the bus from the buffer to the memory card.

The main reason I'm asking is that when taking sports photos in high speed burst mode in RAW, the buffer fills up *very* quickly (as would be expected). That's not the problem. The problem comes in writing the data out to my 4GB Sandisk Ultra II. It's rated by SanDisk at being to do sequential read and writes at up to 15MB/s. The Extreme III cards can do sequential read and writes up to 30MB/s, and the Extreme IV cards can do sequential read and writes up to 40MB/s.

But, if the bus from the buffer to the memory card on the 40D can only move 20MB/s, then investing in an Extreme III would essentially be a waste as it would only give me an additional 5MB/s. But, if the bus between the buffer and the mem card on the 40D can move 40MB/s, then investing in at least an Extreme III if not an Extreme IV for Sports Photography might not be a bad idea at all.

Does anyone know the speed of the bus on the 40D that runs from the buffer to the mem card?

Thanks in advance

This data shows how long you can expect to wait. It varies by card. The rate in MB per second appears to vary by source, but is almost certainly less than 20MBps

They are no difference in writing speed (that is the time taken by the camera to write the photos from the buffer to the memory card) of the Sandisk Extreme 3 and 4 (10.1 MB against 10.9 MB/s), however, your card is much slower, only about 6.5 MB/s

So, am I reading this chart correctly? It takes approximately one second to write a RAW or Large/Fine JPEG to a memory card? So, a burst of 17 RAW shots would take near 20 seconds to write to the card? I can't imagine waiting a full minute to clear the buffer if firing in JPEG mode.

I am reading that correctly, right? That just seems so slow. That's actually slower than the Ultra II be written to. Based on the estimated file size for a RAW image in the specs section of the 40D Manual, we're lookin more like 10MB/s to 11MB/s. Once again, am I reading that correctly?

40d write speeds with different cards:
http://www.robgalbrait​h.com …ti_page.asp?cid​=6007-9257

FlipsidE wrote in post #5859599
So, a burst of 17 RAW shots would take near 20 seconds to write to the card?

No because the camera will start writing to the card while you're still taking shots. It will start writing directly after the first image was taken.

Mil wrote in post #5859579
They are no difference in writing speed (that is the time taken by the camera to write the photos from the buffer to the memory card) of the Sandisk Extreme 3 and 4 (10.1 MB against 10.9 MB/s), however, your card is much slower, only about 6.5 MB/s

Hmm... Now, I don't know how the 40D actually writes data to the card. Not sure what file system it uses, or how it uses space (my guess is that it would do sequential writes of buffer flushes), but this info is from SanDisk's website on their Ultra II cards:

• Minimum of 10MB/second** sequential read speed for ultra-fast image viewing and data transfer
  
• Minimum 9MB/second** sequential write speed lets you capture large image files faster

sth_ wrote in post #5859608
40d write speeds with different cards:
http://www.robgalbrait​h.com …ti_page.asp?cid​=6007-9257

No because the camera will start writing on the card directly after the first shot, even if you continue shooting.

Gotcha! So we're looking at only a difference of about 2MB/s to 2.5MB/s between what I have now and an Extreme III or Extreme IV.

OK, so according to Canon's estimates, full burst RAW = approximately 211MB before the buffer is full. Time to flush the buffer using an Extreme IV is approximately 20s. Time to flush the buffer using an Extreme III is approximately 22. Time to flush the buffer using an Ultra II is approximately 26s.

Very interesting! Thanks for the link!

FlipsidE wrote in post #5859599
So, am I reading this chart correctly? It takes approximately one second to write a RAW or Large/Fine JPEG to a memory card? So, a burst of 17 RAW shots would take near 20 seconds to write to the card? I can't imagine waiting a full minute to clear the buffer if firing in JPEG mode.

I am reading that correctly, right?

You're probably looking at a different chart. The sections entitled Burst of .... show typical timings for buffer clearance. And as has been stated, the buffer will start to clear as soon as it's used, like buffers are designed to do.

In practice, it's all fairly unimportant. I can't imagine wanting to reel off as many as 17 shots immediately after a previous 17 shots. That's trigger happy!

Ade H wrote in post #5859704
I can't imagine wanting to reel off as many as 17 shots immediately after a previous 17 shots. That's trigger happy!

Ever seen how fast skateboarders pull off tricks in succession? I'd say an experienced boarder could probably throw a kickflip, heelflip, shuvit, push a couple times to get a little more speed, throw a 180 ollie followed by a fakie ollie to land in a manual, ride it for a bit, then heelflip out, all followed by a half cab to get back into regular riding position.

Thing is, *all* of those tricks could be done in the same amount of time if not less time than it takes to clear the buffer just once on a 17 shot burst. In other words, it's not trigger happy... it's just trying to keep up with a sport that moves extremely fast. As far as number of tricks landed in a 20 second period of time, a freestyle boarder could put a street boarder to shame. Just think about all the action you're missing while waiting for the buffer to clear.

Edit: Begins to make ya wonder if skateboarding photographers (which is something I would really like to dabble in) should just invest in a 300fps video camera and pull stills from captured video. Better chance of catching all the action.

As you may know, I sometimes photograph motorsports and extreme sports. I have hardly ever filled the buffer at those events.

Ade H wrote in post #5859772
As you may know, I sometimes photograph motorsports and extreme sports. I have hardly ever filled the buffer at those events.

Just out of curiosity, which extreme sports?

BMX vert, street, and dirt; skate street; MTB downhill and trials; freshwater watersports; and MX. And if I ever get to an FMX event, I'd love to shoot that, but it never seems to happen in the UK. You're lucky that you have a lot of FMX events in the US.

Ade H wrote in post #5859838
BMX vert, street, and dirt; skate street; MTB downhill and trials; freshwater watersports; and MX. And if I ever get to an FMX event, I'd love to shoot that, but it never seems to happen in the UK. You're lucky that you have a lot of FMX events in the US.

Now, please don't think I'm trying to belittle what you said earlier because I'm not. And, I apologize in advance if I come across that way.

I'm highly impressed that you can use a 40D to capture all of the action in street skating without filling up the buffer. That takes a lot of talent and a lot of experience that I just don't have. You never know when a street skater is going to throw a trick or what it might be. So, being able to follow him/her on all of their tricks capturing great shots is truly masterful. I'm extremely impressed... extremely!

The rest of the sports you mention are a good bit more predictable. Wakeboarding, for example. It's easy to tell when someone is about to do a trick if they are cutting hard toward the wake. And, usually, the buffer has time to refill *enough* in between wakeboarding tricks to get the next trick (use to ride myself and have seen a few videos of the pros in action). The rest of the sports you mentioned either don't change very quickly (again, not trying to belittle) or are very predictable as to when the "money shots" are coming.

Street skating, though... *any* (and I mean *any*) small advice you could give me on photographing street skaters would be very very much appreciated!

This bus you are talking about is more complicated than a simple one that goes between the northbridge of your computer processor and the ram. It's closer to a PATA interface with some redundancy nuances, where you have a a buffer, a controller, a connection, another controller, another buffer, the actual data storing, varification, etc. That means slower transfers and even cards rated at faster than actual performance will be slower than faster rated cards. A lot like a Velociraptor drive vs a Caviar drive. UDMA cards in a UDMA capable camera will be able to write faster because the drive is "mounted" into the camera, which also means more chances for data corruption on a cheap card (likely not significant in sandisk/lexar cards).

As for sports photography, it's all about keeping focus and timing rather than filling up buffers. The more you know your own sport, the better you'll be at timing, so don't expect to be great if you don't know the sport all that well. Also, don't go shooting without expectations on what you want to shoot. If you say,"Today I'll shoot trick X," don't just shoot V and W because they come before, Y and Z because they come after X. Try to shoot just X. While you might miss some stuff, you'll get better at predicting patterns in their tricks, and then you can shoot just single frame for each trick rather than 6.5fps for two seconds and getting everything between as well. It'll save space on your cards and HDD too

I'm not sure about the 40D, but I compared my own Ultra II, Extreme III and Extreme IV cards in doing a 5fps burst of about 8 frames at 21MP RAW on my 1Ds mark III. The Ultra II took about 20 seconds to clear the buffer, the Extreme III was about 16 seconds, and the Extreme IV was 11 seconds. There are a lot of factors involved so your mileage may vary, but this was an unscientific test done just in my living room. I was trying to figure out if it was worth spending the HUGE extra premium for the Extreme IV cards over the Extreme III.