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jbloom Gold Member Awarded for the continuous and generous sharing of his high level expertise and his always encouraging comments in several forums. Nikonian since 15th Jul 2004Mon 04-Mar-13 03:08 PM
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"D7100 buffer guesstimates"


Wethersfield, US
          

Let me start off my saying there is a fair amount of speculation and hand-waving in what follows. If that doesn't interest you, move along -- nothing to see here! Plus, this will be moot in a few weeks when actual performance numbers start to come in.

Something jec6613 said got me to thinking. One possible explanation for the seemingly low buffer counts of the D7100 is that Nikon expects to be able to write data to the SD card much faster than in, say, the D7000. If that's the case, I wondered, just how much faster, and what effect would it have?

So, I set out to estimate the time-to-buffer-full for several possible cases. Once the buffer is full, the frame rate drops to whatever rate frames can be written to the card. Up to that point, the camera should be able to capture frames at its rated speed of 6 frames/sec.

The biggest unknown in this estimation is the speed of writing to the card. jec6613 suggests that, theoretically, it should be the rated speed of the card. I chose to examine Sandisk Pro UHS-I cards, rated at 90 MB/s write speed. But existing Expeed3 bodies that can use SD cards don't seem to achieve that, according to Rob Galbraith. He measured the speed of the D800 at 42 MB/s. (Still a lot faster than the D7000's Expeed2 system can do, and appears to be in the ballpark of Imaging Resource's tests of the D600), I would be surprised if the D7100 was slower since it's also an Expeed3 system. I'm not sure if Rob's methodology exactly translates to what I'm trying to figure out, though, so I'm going to also consider an intermediate speed of 60 MB/s. The three write speeds considered are, therefore:

42 MB/s
60 MB/s
90 MB/s

The calculation is fairly straightforward and is done in three parts:

Buffer-emptying rate (BER) in fps is calculated as card speed/file size. The file sizes I used are the ones from the D7100 spec sheet for the modes chosen.

Buffer-usage rate (BUR) in fps is the rate at which the buffer is filled minus the rate at which it is emptied (BER). Since the frame rate of the camera is taken to be 6 fps, this becomes simply:
BUR = 6 - BER

Finally, the time-to-buffer-full (TBF) is calculated as buffer size (in frames) divided by the BUR. The buffer size for each mode is also taken from the D7100 spec sheet.

In these tables, I show these values for the worst-case raw scenario of lossless-compressed 14-bit (28.5-MB files, buffer = 6) and the best-case raw scenario of lossy-compressed 12-bit (20.2-MB files, buffer = 9.)

14-bit lossless (28.5 MB files, 6-frame buffer)

Write
Speed

BER (fps)

BUR (fps)

TBF (sec)
42 MB/s42/28.5 = 1.56-1.5 = 4.56/4.5 = 1.3
60 MB/s60/28.5 = 2.16-2.1 = 3.96/3.9 = 1.5
90 MB/s90/28.5 = 3.26-3.2 = 2.86/2.8 = 2.1


12-bit lossy (20.2-MB files, 9-frame buffer)
Write
Speed

BER (fps)

BUR (fps)

TBF (sec)
42 MB/s42/20.2 = 2.16-2.1 = 3.99/3.9 = 1.5
60 MB/s60/20.2 = 3.06-3.0 = 3.09/3.0 = 3
90 MB/s90/20.2 = 4.56-4.5 = 1.59/1.5 = 6


So, what does this show? One thing it shows is that the write speed may have a significant effect on buffer usage. Let's say that Nikon manages to achieve the 60-MB/s write speed. As the table shows, for 12-bit lossy compression, that would give you about a 3-second continuous burst. That compares favorably to the D300s continuous burst for 12-bit lossy, according to Imaging Resource. Obviously, we won't know the actual performance until people get D7100's into their hands and test them out. If the write speed is in the realm of what we have seen with the D800 and D600, then yes, the buffer seems on the smallish side. But if Nikon has upped the write speed, it would explain why the buffer is so seemingly small, and some of the angst about it may prove to be misplaced. We can hope, anyway.

It may be worth pointing out that along with the tradeoff between continuous burst length and raw modes (12 vs 14 bit, lossy vs lossless), another possible tradeoff is reducing the frame rate. At 5 fps, the 12-bit lossy, 42-MB/s value jumps from a 1.5-second burst to a 3.1-second burst. So if your subject can be captured nearly as well at 5 fps, that may be a tradeoff worth making. (That reasoning applies to any body to some degree.)

Finally, it's worth considering how the 1.3-crop mode performance might look. Using the same approach, I calculated burst lengths for the 42 MB/s write speed and the 7 fps of the crop mode:

14-bit lossless (18.8-MB files, buffer = 8): 1.7 s

12-bit lossy (13.4-MB files, buffer = 14): 3.6 s

So... food for thought.

-- Jon
Wethersfield, CT, USA
Connecticut High School Sports Photos

  

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Replies to this topic
Subject Author Message Date ID
Reply message It doesn't seem to work like that...
Jim Pearce Silver Member
04th Mar 2013
1
Reply message RE: It doesn't seem to work like that...
jbloom Gold Member
04th Mar 2013
2
     Reply message Compressibility could be a big variable...
Jim Pearce Silver Member
04th Mar 2013
3
Reply message RE: D7100 buffer guesstimates
jec6613 Silver Member
04th Mar 2013
4
Reply message RE: D7100 buffer guesstimates
dagoldst Silver Member
10th Mar 2013
12
Reply message RE: D7100 buffer guesstimates
Toyse_Woody
05th Mar 2013
5
Reply message RE: D7100 buffer guesstimates
kuzzy Silver Member
06th Mar 2013
6
Reply message RE: D7100 buffer guesstimates
jbloom Gold Member
06th Mar 2013
7
     Reply message RE: D7100 buffer guesstimates
kuzzy Silver Member
07th Mar 2013
8
Reply message RE: D7100 buffer guesstimates
dagoldst Silver Member
10th Mar 2013
9
Reply message RE: D7100 buffer guesstimates
billD80 Silver Member
10th Mar 2013
10
     Reply message RE: D7100 buffer guesstimates
dagoldst Silver Member
10th Mar 2013
11
          Reply message According to IR the D7100 supports them...
Jim Pearce Silver Member
10th Mar 2013
13
               Reply message RE: According to IR the D7100 supports them...
dagoldst Silver Member
11th Mar 2013
14
                    Reply message I'm going by Nikon's numbers here...
Jim Pearce Silver Member
11th Mar 2013
15
                         Reply message RE: I'm going by Nikon's numbers here...
dagoldst Silver Member
11th Mar 2013
16

Jim Pearce Silver Member Nikonian since 02nd Mar 2004Mon 04-Mar-13 04:21 PM
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#1. "It doesn't seem to work like that..."
In response to Reply # 0


Grimsby, CA
          

Nikon seems to factor in writing to a "normal" card in calculating the buffer. There also seems to be a variable lag in writing (which shows up once the buffer is full) - check out some the Performance tests at Image Resources: http://www.imaging-resource.com/PRODS/nikon-d800/nikon-d800A6.HTM .

I would add that most RAW shooters will shoot either 12 or 14 bit lossless. The only silver lining here is that with the enhanced speed from a 95MB/s card the buffer emptying time could be quite short. For instance, a D300s with a fast card can shoot three cycles of 17 frames at full speed in 30 seconds. It could be that in 1.3x crop mode and 12 bit lossless a D7100 could shoot five cycles of 12 shots at a full 7 fps. And in DX mode it might be able to approach 6 cycles of 7 shots at 6 fps in 30seconds.

Jim

  

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jbloom Gold Member Awarded for the continuous and generous sharing of his high level expertise and his always encouraging comments in several forums. Nikonian since 15th Jul 2004Mon 04-Mar-13 05:12 PM
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#2. "RE: It doesn't seem to work like that..."
In response to Reply # 1


Wethersfield, US
          

>Nikon seems to factor in writing to a "normal" card
>in calculating the buffer.

You may be right. I notice on my D7000 that going to 12-bit lossy mode doesn't show the same number of buffer frames in the camera as are shown in the manual. But if the numbers aren't exact, the effect is still present. Writing faster to the card clears the buffer more quickly. This is obvious if you compare fast and slow cards in a camera. For example, with a Sandisk 95 MB/s UHS-I card in my D7000 in 12-bit lossy mode where the camera shows a buffer of 11, I can go about 18 shots before things slow down. With a crappy old SD card (not sure of the speed), I get about 13 shots.

>I would add that most RAW shooters will shoot either 12 or 14
>bit lossless.

How do you know that? Anecdotally, I know plenty of raw shooters who use the lossy modes. And I think if the tradeoff of going to lossy compression is a substantially higher frame rate, many would choose to make that tradeoff. Even at 12-bit lossy you are gaining most of the advantages of using raw.

-- Jon
Wethersfield, CT, USA
Connecticut High School Sports Photos

  

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Jim Pearce Silver Member Nikonian since 02nd Mar 2004Mon 04-Mar-13 10:40 PM
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#3. "Compressibility could be a big variable..."
In response to Reply # 2


Grimsby, CA
          

I assume that IR uses a standard test scene. As to which modes people use, I only know that wildlife shooters using the d300/s tend to use 12 bit lossless, while those using the D800 tend to shoot 14 bit lossless. But it does raise an interesting question when dealing with the D7100's restrictive buffer - whether 14 bit lossy or 12 bit lossless would make for better pictures?

Jim

  

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jec6613 Silver Member Nikonian since 12th Feb 2013Mon 04-Mar-13 11:55 PM
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#4. "RE: D7100 buffer guesstimates"
In response to Reply # 0
Mon 04-Mar-13 11:57 PM by jec6613

Norwalk, US
          

>The biggest unknown in this estimation is the speed of writing
>to the card. jec6613 suggests that, theoretically, it should
>be the rated speed of the card.

Just a point of order: it's the maximum speed of the card, not the rated speed. Sandisk writes sequential raw data to their cards to measure write speed, while in the real world writing a file is a transactional affair that involves multiple read and write operations. Also, there's the efficiency in the firmware of handling those transactions. As newer, faster cards than the Extreme Pro come out, you should expect further improvements in performance, as there is room to grow in the hardware. So if you get 45 MB/s on those 90 MB/s cards, at 150 MB/s you should see 75 MB/s real world speeds.

One thing of interest is that even with Expeed 2 cameras, faster cards were still faster, with the Extreme Pro being faster than the Exteme and so on, suggesting that most of Expeed 3's improvements are mostly firmware and efficiency of the software rather than card interface hardware.

  

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dagoldst Silver Member Nikonian since 02nd Dec 2012Sun 10-Mar-13 07:17 PM
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#12. "RE: D7100 buffer guesstimates"
In response to Reply # 4


Little Rock, US
          

>transactional affair that involves multiple read and write operations

What sort of reads is the camera doing while flushing frame buffers to the SD card?

David

"Sawed that board three times and it is still too short... "

  

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Toyse_Woody Registered since 20th Feb 2013Tue 05-Mar-13 01:13 PM
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#5. "RE: D7100 buffer guesstimates"
In response to Reply # 0


Fort Worth, US
          

Not that I have much to add other than here are some numbers from this weekend shoot at the track that I will use for comparison when my D7100 comes in.

D300 shooting at continuous burst, Raw at 12-bit lossy with 80-200 2.8 lens, SanDisk Extreme IV 8GB CF card at fast turbo drag bike .

I performed a continuous burst of 21 frames before I audibly heard the camera slow down . The image sizes are 4288 x 2848, 1/1000 at f5, ISO 200 and the file sizes are ranging between 11.5 mb to 12.5 mb .

Unless the action dictates I only shoot burst of 3 to 5 frames to capture the shots I need .

  

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kuzzy Silver Member Nikonian since 12th Dec 2005Wed 06-Mar-13 01:02 AM
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#6. "RE: D7100 buffer guesstimates"
In response to Reply # 0


Milford, US
          

Jon, Just curious. You do not seem like a mash the shutter guy when shooting sports in general. That is not to say that on occasion you don't go this route. How restrictive have you found the D7000 buffer in practical applications. I have never had much of an issue with it as I tend to shoot in short bursts of say 3-4 frames then release the shutter for a moment and then maybe another short burst.

I would doubt that the D7100 will be noticeably worse than the D7000 when it comes to maximum burst rate, I also will find it hard to believe that it will be noticeably better either unless this is truly the highest performing DX camera Nikon plans to have in the line. One hint might be that with image quality set to Jpeg large the buffer capacity of the D7100 will hold more images than the D7000 even though the file sizes are slightly larger. That being the case it is going to come down to write speed as it would appear that the physical buffers are about the same in size.

What kind of performance are you looking for to fit your needs?

Regardless, an interesting exercise. It will be even more interesting to see how close you come to reality once people have a chance to test them out.

Marc
There are always two people in every picture: the photographer and the viewer.-Ansel Adams

http://500px.com/WhatISaw
http://kuzzy.smugmug.com

Visit my Nikonians gallery.

  

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jbloom Gold Member Awarded for the continuous and generous sharing of his high level expertise and his always encouraging comments in several forums. Nikonian since 15th Jul 2004Wed 06-Mar-13 07:00 AM
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#7. "RE: D7100 buffer guesstimates"
In response to Reply # 6


Wethersfield, US
          

Marc, you are right about my approach to sports shooting. I don't usually shoot long continuous bursts. However, I may shoot a number of 3- to 7-shot bursts in rapid succession as the play unfolds, especially in sports where the action is continuous, such as lax or soccer. Those, too, can fill the buffer.

That said, most of my sports is shot in JPEG these days, and because of that the D7000 buffer hasn't really been a problem. I resort to raw only when I'm in a situation where exposure or color balance is iffy. But those tend to be low-light situations where I'm shooting the D3 exclusively or primarily, anyway.

I do shoot other things besides sports, though, and there have been a few occasions shooting wildlife when I've strained at the leash that the buffer imposes just enough to appreciate how frustrating it would be to have to deal with it all the time. (That's true of my D3 as well, which also has a smallish buffer.) I'm thinking of situations such as the long, low takeoffs of trumpeter swans. It's useful to be able to shoot a burst of 5-plus seconds to follow a pair of birds as they fly together, hoping to capture moments when their wings are the the same angle for that "in sync" shot. And there are many, many other examples in wildlife shooting where you want bursts longer than I, at least, need for sports. (Airshows are another subject where I find long bursts sometimes useful, although I tend to use a slower frame rate for those.)

For me, personally, though, this is mostly an intellectual exercise. The more I understand about these devices the more I'll be able to wring out of them when I do approach their limits, even if it's only rarely.

-- Jon
Wethersfield, CT, USA
Connecticut High School Sports Photos

  

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kuzzy Silver Member Nikonian since 12th Dec 2005Thu 07-Mar-13 09:34 PM
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#8. "RE: D7100 buffer guesstimates"
In response to Reply # 7


Milford, US
          

I have never really tried to capture Birds in Flight but I can certainly understand why those long bursts would be very beneficial. With the upgrade to the AF system it would seem that the D7100 would be better suited to BIF than the D7000 but without the ability to shoot longer bursts would only be halfway there.

I understand the intellectual curiosity as well, that's why I bother to read as many posts as I do. You never know what you can pick up that might be just what you need in a given situation. I am sure once a couple of people get the new camera in their hands we will quickly get the answer to your guesstimates.

Marc
There are always two people in every picture: the photographer and the viewer.-Ansel Adams

http://500px.com/WhatISaw
http://kuzzy.smugmug.com

Visit my Nikonians gallery.

  

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dagoldst Silver Member Nikonian since 02nd Dec 2012Sun 10-Mar-13 06:18 PM
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#9. "RE: D7100 buffer guesstimates"
In response to Reply # 0
Sun 10-Mar-13 07:43 PM by dagoldst

Little Rock, US
          

> I chose to examine Sandisk Pro
>UHS-I cards, rated at 90 MB/s write speed.

UHS-I cards are rated at 45MBytes per second at 100MHZ, not 90 - I am not sure how Sandisk is making that claim unless it is the UHS-104 spec, (clocking at 208Mhz).

http://en.wikipedia.org/wiki/Secure_Digital#UHS_Speed_Class

My own rough calculation is that a single 14 bit image from a D7100 is 42.8Mbytes, so that would indicate that within 5 shots, (published buffer size), the card would be writing about 1 image per second, assuming wire speed processing through the ASIC architecture of the expeed processor.

If the D7100 supports UHS-104, it would about double the performance once the buffer is full to around 2 frames per second.

Finally, the real cure appears to be UHS-II, at 312Mbytes/sec, (again, if the ASIC processes that fast). I can't find any card like that yet, hopefully it will be out soon.

Edit to add - I am guessing the D7100 does not support the speed of UHS-II. I found that in the teardown of the D600, it uses a chip for the SD interface that is UHS-1 only...

http://guide-images.ifixit.net/igi/GpMPdA4bDfTXCARM.huge - chip is outlined in dark blue

link below is to the actual chip specs

http://product.inrevium.com/sd/te4302.html

I am guessing the D7100 shares a near identical chipset as the D600.

Edit again...

Some bad news - reading the chart for the TE4302 chip, it runs at the 100mhz speed, so at least for the D600, it is a waste of money to buy the UHS-104 spec cards. Again, I am guessing that will be the story for the D7100.

David

"Sawed that board three times and it is still too short... "

  

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billD80 Silver Member Nikonian since 22nd Jan 2007Sun 10-Mar-13 06:58 PM
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#10. "RE: D7100 buffer guesstimates"
In response to Reply # 9


US
          

>UHS-I cards are rated at 45MBytes per second at 100MHZ, not 90
>- I am not sure how Sandisk is making that claim unless it is
>the UHS-104 spec, (clocking at 208Mhz).

I just received 2 SanDisk 8GB SDHC UHS-1 cards, claiming 95MB/s/633X.

I'm not a big fps shooter, but I'll be curious to try these on the D7100.

www.billkeane.zenfolio.com

  

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dagoldst Silver Member Nikonian since 02nd Dec 2012Sun 10-Mar-13 07:11 PM
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#11. "RE: D7100 buffer guesstimates"
In response to Reply # 10
Sun 10-Mar-13 07:46 PM by dagoldst

Little Rock, US
          

Bill,

Yeah, I see they make them - UHS-104 spec is an enhancement to the UHS-I - I am curious to see if they perform any better in the D7100 so let us know.

David

"Sawed that board three times and it is still too short... "

  

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Jim Pearce Silver Member Nikonian since 02nd Mar 2004Sun 10-Mar-13 10:27 PM
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#13. "According to IR the D7100 supports them..."
In response to Reply # 11


Grimsby, CA
          

Going by Rob Galbraith's numbers the D7000 actually writes at around 26 MB/second with this card. So, I'm expecting a best case scenario of about 2 12 bit lossless NEFs per second - assuming a doubling of the actual write speed. So, we could see the buffer clearing (7 shots) in as little as 4 seconds. This could lead to reasonable performance, at least for a short burst approach - and especially in 1.3x crop mode where the buffer will hold 12 12 bit lossless. I'm hoping to know this week.

Jim

  

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dagoldst Silver Member Nikonian since 02nd Dec 2012Mon 11-Mar-13 12:44 AM
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#14. "RE: According to IR the D7100 supports them..."
In response to Reply # 13


Little Rock, US
          

Jim,

If the D7100 uses the same SD I/O chip as the D600, then when the buffer is full, the frame rate at full sensor size/color depth will fall to... 45Mbytes/sec. That is roughly 1 frame per second.

David

"Sawed that board three times and it is still too short... "

  

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Jim Pearce Silver Member Nikonian since 02nd Mar 2004Mon 11-Mar-13 02:19 AM
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#15. "I'm going by Nikon's numbers here..."
In response to Reply # 14


Grimsby, CA
          

The size of a 12 bit lossless NEF is 22.7 MB. So, 2 frames/second.

Jim

  

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dagoldst Silver Member Nikonian since 02nd Dec 2012Mon 11-Mar-13 10:50 AM
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#16. "RE: I'm going by Nikon's numbers here..."
In response to Reply # 15
Mon 11-Mar-13 11:14 AM by dagoldst

Little Rock, US
          

>The size of a 12 bit lossless NEF is 22.7 MB. So, 2
>frames/second.

Sounds about right, however, with my D600, when I hit 20 frames in 12 bit lossless, it slows to about 1 frame a second. I just tested it.

I think the thing I was hoping for is that the D7100 would have a newer UHS-2 chip in it - that remains to be seen.

Edit to add - the D600 produces about a 26MB file in 12bit lossless, so that would have some effect. For clarification, I have the SanDisk Extreme UHS-1 cards, rated at 45MB/Sec - Imaging Resource used the 95MB/Sec card and cleared the buffer in 0.51 seconds - which would give the 2 frame per second rate.

David

"Sawed that board three times and it is still too short... "

  

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