5D Mark III SD limitations.

Has anyone determined what is the realistic write speed of the SD card Slot is when used in conjunction with CF? We know that it has a limitation, but what?
No sense of buying the top of the line if you must slow down.

Thanks.

133x, does not support UHS1...fyi don't write to both cards at the same time as many have said the write speeed defaults to the SD's speed.

If writing to both, what is the optimal write speed of the SD card ?

The write speed is always slow to the SD as the specs were posted prior. It is not the CF card that is slowing down the write, it is the SD card interface. If you want fast, use only CF.

I used my 5DIII last week and the files are still writing to the SD card

Nick5 wrote in post #16872147
No sense of buying the top of the line if you must slow down.

"top of the line" what? Camera, sd card or cf card?

I hardly ever write to the CF and SD card at one time, but when I did it was plenty fast enough.

Speed comes into play when you fill the buffer and want it to empty out quickly. If you don't ever do bursts and fill the buffer, the sd write speeds aren't that critical.

TeamSpeed wrote in post #16872448
Speed comes into play when you fill the buffer and want it to empty out quickly. If you don't ever do bursts and fill the buffer, the sd write speeds aren't that critical.

It also makes a difference what files that are configured to be written to that SD card. If only JPEG images are written, then there isn't much data to write.

Nick5 wrote in post #16872147
No sense of buying the top of the line if you must slow down.

Tell that to the McLaren dealer out in East Goshen...

John from PA wrote in post #16872508
Tell that to the McLaren dealer out in East Goshen...

The only good car analogy here would be that you buy a race car, but its speed is governed to 20mph and you cannot alter it. Ditto on the sd card purchase...

TeamSpeed wrote in post #16872513
The only good car analogy here would be that you buy a race car, but its speed is governed to 20mph and you cannot alter it. Ditto on the sd card purchase...

this... but only when you use the valet key (in this case a SD card) using the regular key (CF slot) you get full speed ahead.

TeamSpeed wrote in post #16872513
The only good car analogy here would be that you buy a race car, but its speed is governed to 20mph and you cannot alter it. Ditto on the sd card purchase...

Except that while a fast SD card will not give much of a gain in the camera, it can still speed up the transfer of the photos to some other media and then quickly be ready for new photos.

pwm2 wrote in post #16872528
Except that while a fast SD card will not give much of a gain in the camera, it can still speed up the transfer of the photos to some other media and then quickly be ready for new photos.

Sure, that is a side benefit but not really in the scope of this discussion is it?

The Veyron has a special key that you have to insert after you have stopped the car, and once you put in that key, it hunkers the car down, switches over to some new fuel, timing, and boost maps, and changes the suspension, then you can hit that 275mph limit. So we can add that to the discussion for fun.

Ah, you just want to brag about your car. Admit it!

TeamSpeed wrote in post #16872612
Sure, that is a side benefit but not really in the scope of this discussion is it?

The Veyron has a special key that you have to insert after you have stopped the car, and once you put in that key, it hunkers the car down, switches over to some new fuel, timing, and boost maps, and changes the suspension, then you can hit that 275mph limit. So we can add that to the discussion for fun.

The OP did write: "No sense of buying the top of the line if you must slow down."

And my post specifically shows that there are reasons for buying better than what the camera can use, because the use inside the camera is often not the only use there is.

Another issue here is that the top-of-the-line boosts a very high transfer speed, but a speed that can only be attained if the flash memory is erased so the card can directly store new information without having to wait for any memory erases. One result of this is that a very fast card - several times faster than the best transfer rates possible by the camera - has a better chance of managing the required continuous transfer rates the camera need if recording video. The faster flash memory chips means that the flash controller can manage to just buffer some data while waiting for a flash erase, then lightning-quickly write down the data and start working on next batch of data.

So in the end, a card with twice as claimed write speeds than the camera can make use of normally tends to give a higher transfer speed inside the camera, than a camera that has a similar claimed transfer speed as the camera is capable to use. All because the faster memory chips means that there will be fewer percent of the time where the memory card has to signal "sorry, you have to wait with sending more data - I'm busy".