Z7 buffer and CFexpres
Fri 14-Sep-18 09:47 AM
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#1. "RE: Z7 buffer and CFexpres" | In response to Reply # 0
Fri 14-Sep-18 10:46 AMI've made several posts that the scenario you described was likely to be the case and was the logic for the small buffer. I'm very sure Nikon engineers designed for CFExpress and Nikon was planning that all along. The common form factor of XQD made it a good interim step - and completely viable for whatever time it takes for CFExpress cards to be available.
Right now we have an in camera write speed of around 240 MB/s on the D5 writing to a fast XQD card - a 400 MB/s card (slightly slower on the D500 and D850). The starting point for CF express is twice the speed of XQD. If that translates to the new cameras, we should see write speeds of over 400 MB/s.
12-bit files from the Z7 will be around 45 MB each, so 9 files at maximum burst rate will be around 405 MB/s. At that speed, the images can all be written to the card without using the buffer.
The math for the Z6 is similar. 12 bit files will be around 26 MB, so 12 files per second will generate 310 MB. That's easily written to a CF card without using the buffer.
If you had included a second card with backup mode as an option, everything is thrown off. Your maximum write speed to two cards is much slower, so you need a large buffer in addition to the second card slot. You were probably adding several hundred dollars to the cost of the camera at retail - just for a backup mode for a few people.
I'm sure Nikon will want to test pre-production CFExpress cards from Delkin and other sources and use that to make sure the firmware performs as planned.
If someone wants 14 bit RAW, they can get the same performance at a slightly slower frame rate, but most of the high speed bursts involve higher ISO levels, so bit depth is not an issue.Eric Bowles
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#4. "RE: Z7 buffer and CFexpres" | In response to Reply # 1
Fri 14-Sep-18 12:54 PM>If you had included a second card with backup mode as an
>option, everything is thrown off. Your maximum write speed to
>two cards is much slower, so you need a large buffer in
>addition to the second card slot. You were probably adding
>several hundred dollars to the cost of the camera at retail -
>just for a backup mode for a few people.
That is the way I have my D750 set up. If I set the second card for overflow, could I expect longer bursts before the buffer fills or would not be really significant?-
#5. "RE: Z7 buffer and CFexpres" | In response to Reply # 4
Fri 14-Sep-18 03:31 PM | edited Fri 14-Sep-18 03:34 PM by ericbowlesThe cameras can only write data at maximum rate to each individual card - and they write sequentially. So if you shoot at 7 fps a 14 bit lossless compressed file, the file is around 30 MB each (around the size of a D750 file) and you are generating 7 files or a total of 210 MB per second until the buffer fills.
The camera can write to one card using a fast UHS-I SD card at 70 MB/s, so it take three seconds to write a one second burst. If you add a second card at the same speed as Backup, it takes an additional three seconds for the backup copy. So every one second burst takes 6 seconds to write to the primary and backup card. And this is with the fastest UHS-I SD cards - other cards may be worse.
If you fill the buffer with a burst of 3 seconds, it will take 18 seconds to clear the buffer. It takes almost one second per image to write the file two times, so until you free up buffer space, your frame rate is limited to 1.1 frames per second (the amount you can concurrently write to two cards).
If you switch to Overflow, you don't have to write to the second card so both writing a second of images and clearing the buffer will be faster. In the scenario above - which is close to your D750 - it would effectively double your frames before the buffer fills and double your frame rate with a full buffer.
Said another way, don't use backup if you are shooting bursts and fast action.Eric Bowles
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#2. "RE: Z7 buffer and CFexpres" | In response to Reply # 0
RECONLEY
Registered since 18th Jun 2012
Fri 14-Sep-18 10:51 AM
For most people a 50 shot buffer would be irrelevant. Something that would allow dozens of 5 shot burst without ever slowing down and a doubling of the speed of the XQD 2 series card would easily do that.
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#3. "RE: Z7 buffer and CFexpres" | In response to Reply # 2
Fri 14-Sep-18 10:58 AMI generally think that's true, but the big factor has been shooting speed with a full buffer or clearing speed to return to something reasonable. For example, the Sony A7r III has a fast frame rate but buffer fills in 3 seconds and a full buffer takes 17 seconds to clear. The write speed is around 2 fps with a full buffer.
My peak needs are usually a series of bursts with a second or two in between bursts. When you have great action, you just keep shooting - sometimes for several minutes. I had a group of owlets last year and made 500 frames in 30 minutes - usually with bursts every few seconds as they were being fed or were moving from tree to tree. Head position, wing position and catchlights are everything with that kind of action, so you want lots of frames.Eric Bowles
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#6. "RE: Z7 buffer and CFexpres" | In response to Reply # 0
Sat 15-Sep-18 12:26 AM
That is interesting, I never heard anyone from Nikon claiming that.
There are reports that when the buffer of Z7 is full, the camera shoots at about 2fps. Since CFExpress is more than twice as fast, it is theoretically possible that Z7 could write 5.5 fps directly to CFExpress, even with buffer full.
There are reports that when the buffer of Z7 is full, the camera shoots at about 2fps. Since CFExpress is more than twice as fast, it is theoretically possible that Z7 could write 5.5 fps directly to CFExpress, even with buffer full.
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#7. "RE: Z7 buffer and CFexpres" | In response to Reply # 6
Sat 15-Sep-18 08:13 AM2 fps when the buffer is full would be far slower than any recent camera if the variables are optimized for normal use. That's probably an incorrect report or reflects a larger than normal file size or a lower end XQD card.
The Sony M card has a peak write speed of around 95 MB/s, so with uncompressed 14 bit RAW you would get a write speed of around 1 fps. Change the same card to 14 bit lossless compressed and you get 1.6 fps. With a 12 bit lossless compressed RAW image, you will get 2.3 fps. Upgrade the card to a Sony G XQD card (actual write speed 220 MB/s in the D500) and you more than double those speeds - to 5.2 fps with the Sony G and 12 bit lossless compressed and 4 fps with 14 bit lossless compressed.
Throughput is limited by the slowest variable - the bottleneck. The file size, the processor, the bus, the PCIE connection, the buffer for processing, the buffer for storage, and the card all impact speed. If any part is not optimized for a faster speed, it limits what can be achieved.Eric Bowles
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#8. "RE: Z7 buffer and CFexpres" | In response to Reply # 7
Sat 15-Sep-18 01:21 PMI need to check fps on my D850 when the buffer is full, it could be similar to what Z7 will provide.
It seems that only 5.5 fps mode allows live viewfinder updates on Z7. Also, when shooting above 400 ISO, 14-bits do not offer an advantage vs 12-bits.
Therefore, if 12-bit lossless compressed can write at 5.5 fps when the buffer is full, the size of the internal buffer becomes irrelevant. Correct?Visit my Nikonians gallery.
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#9. "RE: Z7 buffer and CFexpres" | In response to Reply # 8
Sat 15-Sep-18 02:43 PMThat's correct.
In 12 bit you can pretty well shoot indefinitely at 5.5 fps even once the buffer fills. That's a big advantage compared to most other mirrorless cameras.Eric Bowles
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#10. "RE: Z7 buffer and CFexpres" | In response to Reply # 9
Tue 18-Sep-18 04:46 PMTried it on D850 with fast XQD (Lexar). It does shoot at about 5fps when the buffer is full, but it occasionally stutters (introduces longer pauses while writing to the card), so not really practical to shoot with buffer full (12-bit, compressed).Visit my Nikonians gallery.
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Is it possible that is true and why the Z7 has a small buffer? Is the current buffer a place holder until CFexpress is a reality? Isn't that special?
Bryan