Started Mar 21, 2013 | Discussions thread
MikeFromMesa Senior Member • Posts: 2,849
Re: CF or SDHC

mjack101 wrote:

When I first got my 5diii I put both a CF and an SD card in with the SD card set to write only when the CF card is full i.e. no simultaneous writing. The SD card has never been used.

To utilize the 6fps to its max then a CF card is a must.

The article linked above which talks about write speed to the CF card when an SD card is in the slot is a little misleading although it is corrected in the comments section. Unless the camera is set to write to both cards at the same time then there is no effect on the CF card write speed of merely having an SD card in the slot as well.

Granted. The slowdown is only present when the sd card is written to. There are many ways to configure use of the cards and there is often not enough information available to people setting their cameras up to know what the full results of their choices will be.

1) Use of the second card for "roll-over" (that is, write when the first card is full). This will not have any ill effect on the write speed as long as the sd card is not being used. Further, the burst speed and capacity of the camera will not be affected by the setup. It does not, however, really provide any protection if your primary card fails and thus I don't use it.

2) Use of the second card to make copies of what is being written to the first card (the way it is setup on my camera). This will slow down the write time to the flash memory as the sd card writing will take longer than the cf card, but it will not adversely affect the burst capacity of the camera.

3) Use of the second card to store a different image format than the first card (for example, raw to cf, jpg to sd). This is, as far as I can tell, the worst possible setup for the camera if the user wants to do something like BIF. It seems to divide the camera buffer into 2 partitions, one for raw and one for jpg, and hence lowers the burst capacity of the camera to far fewer images than with any other setup. I found this out only by testing as there does not seem to be any documentation about it.

I really like my 5D3 and think that the ability to make backup copies of my images is very important. I have not lost many images due to camera failure (I lost 2 images with my first 5D3 due to some failure), but prefer to be safe than to be sorry.

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