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Author Topic: SDHC Cards  (Read 812 times)
PDRubner
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« on: April 19, 2014, 04:35:03 PM »
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Can someone provide me with some leaning and insight into SDHC cards?
I have been looking for some faster cards so that the camera’s buffer clears faster when shooting bursts, HDR, or bracketing.  In looking at the B&H web site I see 2 cards with high read/write speeds, but with vastly different pricing and I would like to know why.
The first card is a PDNY 32 gig class 10 card with 95 mbs read and write speed for about $20.  The second card is a Delkin 32 gig Class 1 card that writes at 80 mbs and reads at 95 mbs.  It sells for around $60.
I am shooting with a Pentax K-3 which has a maximum burst speed of around 8+ frames per second (around 37 mb each for RAW) and a good sized buffer (23 frames) but one that is slow to clear (2.2 fps), so we are talking about a maximum write speed of somewhere between 75 and 80 mbs.  The advantage of a fast card is therefore limited by the write time from the buffer to the card.  That being the case, I am not inclined to get too crazy about fast cards past the point where it will do some good.  Perhaps some future firmware update will increase the write speed to the card.
Either card will clear the buffer faster than the camera can write to it, so what is the advantage, if any, of the class 1 card over the class 10 card, or vice versa?
ADDITIONAL INFORMATION ---
I have done some research since the posting and have some information that anyone interested might use for further inquiry.
First, it doesn’t matter which card you use if your camera is not set up to take advantage of the UHS-1 card bus transfer rate.  The UHS-1 card will work but will max out at class 10 speed which only means that the minimum transfer rate is 10 mbs.  What the maximum is depends upon the manufacturer and how the card is used.
Second, there is some confusion over whether a class 10 and UHS-1 card are the same.  Scan Disk says they are and some say they are not.  The UHS designation refers to the maximum speed the bus can carry; class refers to the minimum data transfer rate.  See http://www.dpreview.com/forums/thread/3221163  There are SCHC cards with UHS-I buses and SDXC cards with UHS-I buses.  You may want to look at this Wikipedia posting which sets it out pretty clearly: http://en.wikipedia.org/wiki/Secure_Digital#UHS_Speed_Class
Third, camera manufacturers generally do not provide specific information on the maximum megabytes per second rate at which their cameras are capable of clearing the buffer.  Sometimes you can get a fix on the frame rate at which the buffer will clear for a particular kind of image file and do a little arithmetic but there are some variables so it will be an approximation.
Fourth, there is more than one kind of UHS card: type 1 and type II. Type 1 supports anything from a minimum of 10 “up to” a theoretical 104 mbs); Type II is capable of transfer rates from 30 up to a theoretical 312 mbs. That’s a measure of capability, not actual speed.  It gets more complicated – there are Class 1 and Class 3 UHS cards.  The few UHS-II Class 3 cards available are mostly for 4K video and are very pricey.  Go figure or at least see the explanations and tables in the Wikipedia article referenced above.
Fifth, if you plan on using your card in future cameras, be they still or video, even if your present camera is not configured for SDXC, you should conder buying the most capable card compatible with your camera within reason.  If you choose an SDXC card, it should perform to the Class 10 standard (what ever that is) but make sure the camera can read it as an SDHC card.  Some will not.  Also make sure your card reader can handle an SDXC card if you decide to go that route.  The new stuff likely will be able to use the card’s capabilities.  A UHS-I bus can exist either on a SDHC or a SDXC card, so try to keep track of what you are getting.
All this is more than I ever wanted to know about cards for my cameras.  All I want is what will clear the buffer as fast as possible and work.  Who would have guessed the path to that objective was so long and convoluted?
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« Last Edit: April 22, 2014, 02:43:29 PM by PDRubner » Logged
k bennett
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« Reply #1 on: April 19, 2014, 09:33:39 PM »
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The first question is whether your camera can use the extra speed. I have used Sandisk 45 and 95 mbs cards. Some cameras can take advantage of the extra write speed - my Fuji bodies really need it. But others show zero difference in write speed and buffer clearing times, like my Panasonic GH2.

I don't have any experience with those cards nor with the Pentax. But I have been happy with the Sandisk 95 mbs card.
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