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<blockquote data-quote="WayneF" data-source="post: 227817" data-attributes="member: 12496">I think your only problem is that the interval may need to be 2 or 3 seconds longer than the shutter time.If 20 second shutter, try 23 second intervals.If you are missing shots (if result is fewer shots than calculations predict), then you simply need a longer interval.The interval time includes:1.&nbsp; Shutter duration time.2. time to process/compress the image file.3. time to write the image file to the memory card.&nbsp;&nbsp; If you have a slow memory card, this takes more time.If writing large Raw files to a slow card, you will need a lot more time.&nbsp; Writing 40 MB D800 Raw files to the fastest 1000x memory card needs 3&nbsp; seconds more interval than a long shutter time.&nbsp;&nbsp; JPG is a smaller file to write, but other&nbsp; cameras are slower writing, and certainly other cards are slower writing.&nbsp; No one answer, but you need more than one second.If your interval time is too short, and operations are not complete yet, then it simply skips next interval, and waits for next scheduled interval.&nbsp; Your results will have fewer shots than you planned.&nbsp; Start a short test with interval time being too long.. maybe 5 seconds longer than the shutter time.Then as you see the card writing access LED finish and go out, and&nbsp; you realize there is a lag before the next shutter, then you know about how much you can reduce the interval to reduce that lag.&nbsp; But there needs to be at least a tiny lag time, or it cannot do it.&nbsp; This seems to imply that multitasking and buffering do not apply to interval timer.But a one second lag before next interval starts will not affect star trails.&nbsp;&nbsp; It will make your intervals be very reliable.</blockquote>

[QUOTE="WayneF, post: 227817, member: 12496"] I think your only problem is that the interval may need to be 2 or 3 seconds longer than the shutter time. If 20 second shutter, try 23 second intervals. If you are missing shots (if result is fewer shots than calculations predict), then you simply need a longer interval. The interval time includes: 1. Shutter duration time. 2. time to process/compress the image file. 3. time to write the image file to the memory card. If you have a slow memory card, this takes more time. If writing large Raw files to a slow card, you will need a lot more time. Writing 40 MB D800 Raw files to the fastest 1000x memory card needs 3 seconds more interval than a long shutter time. JPG is a smaller file to write, but other cameras are slower writing, and certainly other cards are slower writing. No one answer, but you need more than one second. If your interval time is too short, and operations are not complete yet, then it simply skips next interval, and waits for next scheduled interval. Your results will have fewer shots than you planned. Start a short test with interval time being too long.. maybe 5 seconds longer than the shutter time. Then as you see the card writing access LED finish and go out, and you realize there is a lag before the next shutter, then you know about how much you can reduce the interval to reduce that lag. But there needs to be at least a tiny lag time, or it cannot do it. This seems to imply that multitasking and buffering do not apply to interval timer. But a one second lag before next interval starts will not affect star trails. It will make your intervals be very reliable. [/QUOTE]

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