Do we really need Sandisk Extereme Pro 95mbps read & 90mbps write speed?

Started Dec 26, 2013 | Discussions thread
Alan_S Senior Member • Posts: 1,834
Re: The calculation says A77 writes at ~ 58 MB/s to SD card

Sam_Oslo wrote:

Alan_S wrote:

with the ~90mbps cards I get test bursts (both a77 & a99) of 17 RAW files before filling the buffer, with buffer clearance in ~7 seconds. Real life shooting .

I can try to calculate the real speed (from buffer to SD card), based on these numbers, if I'm nit mistaking.

A A77 RAW file is ~24MB and if we multiply it with 17, it's equal to total 408 MB.

It means then Camera uses ~7 Sec to write ~ 408 MB, so the actual write-speed is 408 divided by 7, and that's equal to ~ 58 MB/s .

I'm not sure if this is the scientific way for calculating the actual write speed, and these numbers are not exact either, but the result sounds about right to me.

Yeah, would be nice if Sony published the actual maximum speeds in the specifications. I don't doubt your numbers are somewhere in the ballpark (which would make the cheaper 25-30MB/s cards twice as slow as the ExtremePro).

I just tried a simple unscientific test comparing the two cards in my a99: Sandisk Extreme Pro 95MB/s and the Sandisk Extreme 45MB/s; camera set to RAW, hi-speed 6fps burst (hi ISO NR, object tracking, face recognition, lens correction, and DRO all set to OFF). Pressing the shutter down, counting the shots until the buffer filled, then releasing and watching the red light and counting the seconds with a digital watch to clear the buffer... yeah, totally unscientific , but here's what I got (duplicated the test twice with same results):

Sandisk Extreme 45MB/s card: 16 RAW shots, 11 seconds to clear buffer
Sandisk Extreme Pro 95MB/s: 18 RAW shots, 7 seconds to clear buffer

I no longer have anything slower than the 45MB/s card to compare as they were painfully slower than either of these to clear the buffer. So, from the perspective of the ExtremePro's 7-second performance, the 45MB/s card takes 57% longer to clear. Is the faster card worth the extra cost? Well, that's a personal decision, but after spending multiple thousands on bodies & glass, a 57% reduction in performance seems like a lot to swallow just to save 30 bucks

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- AlanS

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