Larry,
Some time ago, I was trying to find answers to similar questions.
Unfortunately, Pentax doesn't provide (at least at that point it didn't)
any specs with respect to this.
So, let me share the most essential bits of information that I was able to
find (and still remember).
First, a few comments:
1. Note that Speed class (Class 10) specifies only the minimum speed and
only for WRITING.
2. An additional classification that is somewhat complementary to theses
classes is the UHS speed classes (UHS-1, and -3)
https://www.sdcard.org/consumers/speed/ .
They specify not only the minimum writing speed, but also the UHS mode of
the SD bus.
3. Note, that you would benefit from how fast you can READ from the cards,
both (a) in the camera and (b) in your card reader.
4. Also, note that SDXC, compared to SDHC also defines a difference in the
file system support (exFAT).
https://en.wikipedia.org/wiki/Secure_Digital#File_system
So, when I was choosing my cards at the end of 2014 (I have k-5 iiS), but
I was considering K-3, so, I had it in mind (somewhat).
My conclusion: to have at least Class-10, UHS-1.[*] I don't remember for
sure if K-5/K-3 support UHS-I mode, but I deemed it to be necessary.
https://en.wikipedia.org/wiki/Secure_Digital#Transfer_modes
I forgot what I decided was the useful writing speed cut-off (I might not
have gotten that number). I vaguely remember thinking in the range of
40-60 MB/s.
(Notice, unlike internet connection speed, it is megabYtes per
second, hence MB, not Mb)
[ Just in case: https://www.sdcard.org/consumers/speed/ says that
"Speed Class and the UHS Speed Class are not compatible", but that is
an ambiguous statement, as the cards include markings for both.]
In any case, the latest card I bought was 64GB Samsung PRO that is
labeled: SDXC, I, (1), and Class 10:
http://www.adorama.com/ISGMBSG64DAM.html .
This card has specs for 90 MB/s - Read, 50 MB/s write.
I've been using it for 10-11 months, and have no complaints. As a matter
of fact, within this time I've used my SanDisk cards only once or twice.
Sorry for the lack of solid number, but I HTH,
Igor
Larry Colen Thu, 15 Oct 2015 16:56:29 -0700 wrote:
Does anyone have any specifications for the bus speed for the SD cards in
our DSLR bodies? Under the rubric of Class 10 cards, different cards are
sold with different data rates. My recent purchases vary from 40 to 90
MbPS. The last time I bought cards, boosting speed from 40 to 80 or 90
cost about as much as going from 32 to 64 GB.
In addition to the speed to transfer the raw files from the buffer to the
card, there is also the speed to process the raw files, so while the bus
might in theory be able to handle 120 MbPS, the system might not work any
faster with a 90M card than with an 80M card.
Has anyone done any specific experimentation on where diminishing returns
come into play on recent bodies (K-5, K-3 ...)?
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