R7 Buffer Management

Started 2 months ago | Discussions thread
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John Sheehy Forum Pro • Posts: 25,926
R7 Buffer Management

There has been a bit of unclear talk about what happens when the buffer fills, so I took at look at what actually happens, which I can see in real time on the display, and also use EXIFTool to get exact timing down to 0.01 seconds since midnight, in a spreadsheet. I made a .CSV file with EXIFTool, imported it into OpenOffice, stripped out hours, minutes, seconds, and hundredths of a second from the text for subsecond original time.

Anyway, the behavior is kind of inconvenient.

If I take an old 4GB PNY SD that is very slow to write to, 30fps ES, and attach a remote release and lock it down in bulb mode, then I get this pattern:

30 frames at 30fps (auto ISO resulted in ISO 8000 with a fast 1/2000 shutter speed)

A pause of 88.39 seconds

11 frames at 30fps

A pause of 143.68 seconds

18 frames at 30fps

A pause of 91.80 seconds

11 frames at 30fps

A pause of 13618 seconds


When I say "30fps" I am not kidding; the time interval in hundredths of a second always follows this pattern without fail: 03 03 04 03 03 04 03 03 04 etc.

So, it seems like the camera might be managing the buffer memory in blocks that hold multiple files, and will not make any of the block available until it is completely empty. Perhaps Canon decided this because their files are variable size? Now, if a camera only shot uncompressed images, the camera could write a single file to the card and know with no calculation that another can take its place in the buffer immediately. That could allow a slower-but-consistent burst to continue after the buffer fills (the single file size is the block), rather than the pulsing of bursts that the R7 does (and maybe other Canons).

I don't see any benefit of pulsing as an end in itself, because when your buffer fills, you are most likely to want the next photos, immediately, while you are still following the same subject. After a few seconds, a pulse has nothing to do with your immediate photographic intentions.

Perhaps there is good reason for Canon's decision that I haven't thought of, but it seems to me that it would be better to have the camera continue shooting as often as it can after the buffer is filled, and perhaps the camera should NOT try to maintain 30fps, but something consistent based on card write speed, if you are still pressing the shutter button from the original press.  I'll have to try again with faster cards and see if this pulsing is still an issue.

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Canon EOS R7
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