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Old Jul 2, 2010, 3:02 PM   #1
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Default SDHC Class 6 vs. SDHC Class 10 with K7

Finally got my camera back from repair. As I posted earlier I broke off the Hot Shoe Attachment when I hit my flash against a shelf. Sent to Arizona (Pentax Repair goes to C.R.I.S. Camera Services), cost $260.00 for repair.

While it was gone I acquired to new items for the K7. One is a 32GB SDHC Class 10 memory card, the other I will cover in another post.

I thought others may be interested in a comparison to see if the increased speed is worth while. My unscientific method was to shoot continuously in DNG Raw until the buffer was full, then time how long the buffer took to empty. Three times averaged with each card ended like this:

32GB SDHC Class 06 - Averaged 23 seconds to clear the buffer.

32GB SDHC Class 10 - Averaged 12 seconds to clear the buffer

For me that makes it worth while.

Ed
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Old Jul 2, 2010, 3:06 PM   #2
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If you take allot of burst action or RAW shots get the class 10. If not, the class 6 will work fine.
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Old Jul 2, 2010, 4:12 PM   #3
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You may want to let members know the cards you used (Brand/Model), as you will tend to see big differences between cards with some cameras.

For example, K7 tests I've seen show full buffer flush times shooting RAW of around 15 seconds with a Lexar Pro Class 6 SDHC card, or around 13 seconds with a Class 6 Sandisk Extreme III SDHC card, or under 10 seconds with a newer 30MB/Second Sandisk Extreme III.

IOW, 23 seconds sounds a bit on the slow side for a Class 6 Card.
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Old Jul 2, 2010, 7:05 PM   #4
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Both of my 32GB HDSC cards are "Topram".

I picked up the Class 10 for $65. I have been using the brand for several years now and have them in 4,8, 16 and 32GB. The 32GB Class six version has no trouble with video recording. I always shoot DNG Raw and often DNG Raw + jpeg so the speed helps. I do not know how the other tests were run, I simply shot DNG Raw as fast as the camera would fire, when it stopped I started timing till the red light went out on the K7.

Ed
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Old Jul 2, 2010, 8:50 PM   #5
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Here's the speeds for classes:

Class 2: 16 Mbit/s (2 MB/s)
Class 4: 32 Mbit/s (4 MB/s)
Class 6: 48 Mbit/s (6 MB/s)
Class 10: 80 Mbit/s (10 MB/s)

This is the guaranteed MINIMUM transfer rate.

The older speed rating was based on the transfer rate of a CD, which is 150KB/s.
So a 150x SD card is 150K x 150 = 22.5MB/s

So looking at the above, the MINIMUM transfer is equivalent to:
Class 2: 16 Mbit/s (2 MB/s) = 13x
Class 4: 32 Mbit/s (4 MB/s) = 26x
Class 6: 48 Mbit/s (6 MB/s) = 39x
Class 10: 80 Mbit/s (10 MB/s) = 66x

The range of speed could be:
Class 2: 16 Mbit/s (2 MB/s) = 13x - 25x
Class 4: 32 Mbit/s (4 MB/s) = 26x - 38x
Class 6: 48 Mbit/s (6 MB/s) = 39x - 51x (I think the last figure is right, just under what would be class 8)
Class 10: 80 Mbit/s (10 MB/s) = 66x +

However, before Class 10 was around, some Class 6 SDHC cards had speeds probably close to, or exceeding Class 10.

It should be noted that a lot of Class 10 SDHC cards would be way slower than an old 150x SD card.

SO it's true that not all Class 10, or even Class 6 cards are equal!!
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Old Jul 3, 2010, 2:45 AM   #6
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Quote:
Originally Posted by dnas View Post

However, before Class 10 was around, some Class 6 SDHC cards had speeds probably close to, or exceeding Class 10.

It should be noted that a lot of Class 10 SDHC cards would be way slower than an old 150x SD card.

SO it's true that not all Class 10, or even Class 6 cards are equal!!
This is all correct, and the "Class" system of speed rating is pretty useless.

I noted the tremendous slowdown in write times per image starting with the K20, about when the "Class" speed ratings started being used. The fastest rated cards were Class 6, and the sustained write times were dismal compared to the 133x SD cards that I had been using with the K10. My problem was that it seemed to take forever to review a shot on the LCD, and with the widely varying lighting conditions with shooting birds as they landed in different areas, I had gotten used to reviewing the first shots with the histogram, and making Ev comp adjustments according to what I saw -- it's pretty frustrating taking a bunch of shots, only to find later that all of them had badly blown out white areas. . .

With the K20 and K-7, I started going withe Sandisk Extreme III 20MB/sec Class 6 cards, since they were the only ones at the time where they advertised actual sustained write speeds, and have stuck with them. I don't run into performance problems shooting jpegs, but have been told that the K-7 is capable of faster write times with the 30MB/sec Extreme IIIs. I cannot confirm this, as by my dismally unscientific tests, I came out with @ 18MB/sec write speeds. I'm satisfied with the 20MB/sec cards.

For reference, I usually shoot *** 14 MP jpegs, have occasion to shoot the occasional Continuous High burst, and have yet to fill the buffer on either the K20 or K-7. I don't use the video mode, so can't comment about what speeds might be required for this mode or either of the RAW formats in continuous shooting.

Scott
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Old Jul 3, 2010, 6:35 AM   #7
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I've been using Transcend Class 6 since I got my K-x. The speed is good enough for me since I still haven't experienced a full buffer while shooting in raw. However I must say I do not use continuous burst a lot.

Carlo
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Old Jul 3, 2010, 10:02 PM   #8
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Lots of useful info here guys, Thanks!
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Old Sep 21, 2010, 4:11 AM   #9
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Learned somthing new today : I can do movie recording on a 4 GB Sandisk class 2 with my new Canon 550D, but with a 8 GB class 4 I can only take 10 secs at a time. Class 2 CAN be faster than class 4.
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Old Sep 21, 2010, 5:33 PM   #10
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Dumb question probably but my SDHC sandisk cards have 2's with a circle around them

Does that mean theyre class 2 or is that like SDHC 2 , similar to like how there is usb 1 and usb 2.0

Ill be really ticked if I spent 36.00 a pop on class 2 16 gig cards when amazon is selling the extreme 3' 8 gigs for 30 with much faster write speeds

Last edited by NMRecording; Sep 21, 2010 at 5:47 PM.
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