Excuse ths question please....

[TheRogue]

This is probably me missing the glaringly obvious but my 5D3 - takes CF and SD cards right?  With the SD cards does it matter if I choose the SDHC or the SDXC?  I know there must be a diference but are they both compatible with the 5D3?

[Peter]

SD, SDHC and SDXC work with 5D III.

When using CF together with a SD in the 5D III, the fastest write speed of your camera will slow down to the write speed of your SD. That means that if your CF can do 100 MB/s and your SD 20 MB/s you will only be able to use 20 MB/s.

[TheRogue]

Oh, so does that work in reverse?  My CF is 160mbs so is it then pointless me getting a quicker SD because one or the other slows the other down?

[Peter]

Fastest CF Canon 5D III can use is 100 MB/s. Fastest SD Canon 5D III can use is 20 MB/s. With both cards in your camera, the fastest write speed will be 20 MB/s.

[TheRogue]

My CF is rated 160mbs - so writes a a maximum of 100 then even without a SD in the slot?  And its pointless me buying a SD, SDHC or SDXC any faster than 20mbs? As long as I understand I can work with it. Ultimate lightening quick write speeds aren't really a priority for me.

[Waddizzle]

If write speeds of memory cards are determined in a way similar to how maximum capacity on floppy disks were determined, then go for the cards with the higher write speeds.

Floppy disks were rated for different storage capacities.  The highest capacity disks were not manufactured any differently from the lowest capacity disks.  In fact, they probably came off the same production line.  Manufacturers would test the disks, submitting them to successively more and more stringent testing.  The result of the testing would be used to determine how the disk capacity would be identified.

In other words, the lower capacity disks failed more quality control tests than disks with a higher rated capacity.  I suspect that memory cards are quite likely tested for speed, and sorted by speed ratings in a similar way.

[TheRogue]

I'm not sure if this makes the previous answer right or wrong. I guess it moves the debate on, as in, its pointless to pays $$$ for a card if it gives $ performance.  I have absolutely no objection buying the bestest fastest most reliable card for $$$ but if the camera doesn't utilise the full speed, performance, feature set, then might as well downgrade, surely?

[Waddizzle · Accepted solution]

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@TheRogue wrote:

I'm not sure if this makes the previous answer right or wrong. I guess it moves the debate on, as in, its pointless to pays $$$ for a card if it gives $ performance.  I have absolutely no objection buying the bestest fastest most reliable card for $$$ but if the camera doesn't utilise the full speed, performance, feature set, then might as well downgrade, surely?

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Good point. 

There isn't any need to buy the most expensive and fastest card out there.  By the same token, one shouldn't invest in cards that are the least expensive that one can find, either.  I try to avoid the off-name brands, too.

[Peter]

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@TheRogue wrote:

My CF is rated 160mbs - so writes a a maximum of 100 then even without a SD in the slot?  And its pointless me buying a SD, SDHC or SDXC any faster than 20mbs? As long as I understand I can work with it. Ultimate lightening quick write speeds aren't really a priority for me.

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I use a SanDisk 45 MB/s in my 6D. I also use a SanDisk 95 MB/s. Maximum write speeds with both cards are 43 MB/s in the camera when I do a benchmark in the camera. But the 95 MB/s was cheaper now than the 45 MB/s was when I bought it.