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SD card type for video on a7r2

Discussion in 'Sony Alpha E-Mount Cameras' started by adwb, Dec 3, 2015.

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  1. adwb

    adwb TalkEmount Regular

    127
    Sep 30, 2015
    Bristol UK
    Alistair
    Why does the a7r2 demand a sdxc class 10 card or uHS1 card, for XAVCS 4K OR XAVCS HD MOVIES?

    why can a sdhc uhs1 card not work?
    I have a sdhc UHS-1 class 10 card but it wont work for the video settings

    SDHC cards offers between 4GB to 32GB and SDXC offers more than 32GB. There is no difference in the quality or security or speed. The transfer speed depends on the "CLASS" of the card mentioned on it and not on whether it is a SDHC card or SDXC.
     
  2. bdbits

    bdbits TalkEmount Veteran

    400
    Sep 10, 2015
    Bob
    From what I have read, SDHC cards use a FAT32 file system. This limits the capacity of the card to 32G, but perhaps more importantly the maximum file size to 4G. SDXC uses exFAT I think, and the capacity and file size maximums go up to 2T (~2000G). Now I am not a video person at all so I do not know enough to make the calculation as to how long it would take to fill up a 4G file - but maybe it is not very long. It is about the only justification I can think of myself, since as you say it is not really a transfer speed or quality issue.

    I was a bit frustrated by this, too, on my recently acquired A6000. I have a very good 16G SDHC card in it, but the camera is quite insistent it is not suitable even for a very short clip. :(
     
  3. dbmiller

    dbmiller TalkEmount Top Veteran

    777
    Mar 2, 2012
    New England
    Yep - Disk format and maximum file size are the reasons for requiring SDHC. And even you if format a 16gb or 32gb card for exFAT, Sony cameras still won't let you use it. Since if you reformat the smaller card in camera, it would go back to FAT32. So they took the "safe" approach of requiring SDHC.
     
  4. WookieeGunner

    WookieeGunner TalkEmount Rookie

    15
    Apr 17, 2015
    An even big piece to the puzzle is the cluster size. Hard Drives (and by extension SD cards since they use Hard Drive file types) store things in blocks called clusters. The maximum cluster size for Fat32 is 16KB, so for every 16KB the camera has to update the File Table. At 32Gigs exFAT uses 128KB clusters so not only does it have to update the FAT table 1/8 as often, it can potentially send data 8X as fast (assuming it writes a cluster at a time). It probably isn't nearly that fast, but it can definitely be faster.