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I tested my Nikon D800 with a SanDisk Ultra 64 GB 80 MB/s SD card.

I have a device which measures time and is triggered by the green LED light on the back of my camera which indicates that it's writing to the memory card. I took an image and measured how long the green light was on. I put the value into a table (shown below) and took the next image. I did this with 10 images and it seemed that the amount of time for saving the image increased with every shot. Here are my results (in seconds):

5.671
6.616
13.740
22.843
22.970
22.360
22.753
22.600
7.189
4.019

Between the green light going off and the next shot, I just put the value into my computer. This took me about 2 to 3 seconds. I can only imagine that the camera needed to clear the buffer or something like that in the meantime.

Maybe the green light switching off does not mean the camera finished all its work.

I was capturing uncompressed 14-bit RAW files. Saving times decreased to about 1 second using a decent CF card as the primary card.

Usually I use this SD card as a second card for saving low-res jpegs as a backup. I did not notice the same slow-down effects using this SD card as the secondary card.

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  • \$\begingroup\$ Does this answer your question? Why does it take more time to write a photo to memory when I shoot in RAW? \$\endgroup\$
    – xiota
    Mar 14, 2020 at 13:02
  • \$\begingroup\$ No it doesnt. I understand that a RAW file is larger and needs more time to be saved. Why does the first photo needs much less time to be saved than the third one? The second pictures was taken a few seconds AFTER the first was saved. The third one was captured AFTER the second one was completely saved. I would understand that the saving time increases for a second image when the first image isn't saved just yet. \$\endgroup\$
    – Arji
    Mar 14, 2020 at 13:13
  • \$\begingroup\$ I would try the test again - but wait much longer between shots and also make sure the picture is the same each time (maybe with the lens cap on?). \$\endgroup\$
    – rrauenza
    Mar 14, 2020 at 14:37
  • \$\begingroup\$ What I tried a few minutes ago: take a picture, wait until the light turns off, wait another 15 seconds and take the next picture. In this case the saving times (or at least the duration the green light stayed on) were approximatively the same. \$\endgroup\$
    – Arji
    Mar 14, 2020 at 17:19
  • \$\begingroup\$ Are these times in seconds or milliseconds? 22,970 seconds is almost six and one-half hours. \$\endgroup\$
    – Michael C
    Mar 15, 2020 at 8:24

1 Answer 1

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This is normal and expected. It's basically queuing theory. Here's an analogy that might help in visualizing this:

If you walk into an empty store (sensor/camera), grab an item (light/data), and get in line (buffer) for the cash register, they'll ring you up right away (write to SD card), and you're on your way.

If you walk into a packed supermarket and grab an item — even if there are n cash registers, if there are more than n people ahead of you when you get in line you're going to have to wait before you leave. All else being equal, the more people in line ahead of you, the longer you'll wait.

Similarly: if the length of time between images captured < the time it takes for the buffer to persist that image to SD/CF card and clear itself, your shot will have to "wait in line". How long is a function of e.g., buffer speed, buffer size, SD card speed, and file size, not to mention other variables like compute power.

Hope this helps!

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    \$\begingroup\$ This would mean the green indication light turning off doesnt implie that the camera is done with the image (which I assumed is what the light turning off again should be indicating). \$\endgroup\$
    – Arji
    Mar 14, 2020 at 14:24
  • \$\begingroup\$ How so? I guess I may have misread your post — when you say "I did this with 10 images and it seemed that the amount of time for saving the image increased with every shot."... how did you determine the duration between shots? Just "when the light turns off, take another and repeat?" \$\endgroup\$
    – Jesse Stuart
    Mar 14, 2020 at 14:52
  • \$\begingroup\$ Every time the light went of my measurement device displayed how long the light stayed on. Instantly I wrote the value to the table. Then I would take the next image. As I said it took me about 2 to 3 seconds to do that. \$\endgroup\$
    – Arji
    Mar 14, 2020 at 17:23
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    \$\begingroup\$ @Arjihad Thanks for clarifying. This may be of interest to you as well — they measure buffer clearing times for this body under a range of conditions. This one came as a surprise to me: "ISO sensitivity and noise reduction settings can also affect cycle times [...]". \$\endgroup\$
    – Jesse Stuart
    Mar 17, 2020 at 2:37

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