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accuracy of timing

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Offline walterjwhite

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accuracy of timing
« on: 27 / January / 2011, 16:20:25 »
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Hi all,

I am using CHDK on a A540 and have a 60 - 70% accuracy with timing which is okay, but will cause jerky video once I stitch it together.

For instance, I have no pictures on 00 seconds, but this is what I do have: (also odd why this pattern is repeated)

02
04
08
10
14
16
20
24
26
30
32
36
38
42
46
48
52
54
58

I am using a simple sleep 2000.

Any ideas?

Walter
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Offline SkyWalker9

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Re: accuracy of timing
« Reply #1 on: 27 / January / 2011, 17:03:37 »
Quote from: walterjwhite on 27 / January / 2011, 16:20:25
I am using CHDK on a A540 and have a 60 - 70% accuracy with timing which is okay, but will cause jerky video once I stitch it together. For instance, I have no pictures on 00 seconds, but this is what I do have: (also odd why this pattern is repeated)

04  08  10  14  16  20  24  26  30  32  36  38  42  46  48  52  54  58

I am using a simple sleep 2000.
In order to determine what is causing this sequence we need to see the script. Please post the script you are using that is causing the re-occuring 2,4,2,4,2,4,4 pattern.
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Offline reyalp

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Re: accuracy of timing
« Reply #2 on: 27 / January / 2011, 17:14:04 »
You should calculate your sleep time, rather than using a fixed time.

something like:
Code: [Select]
t1=get_tick_count()
shoot()
sleep(2000 - (get_tick_count() - t1)
If you are relying on autofocus on a variable scene, you may need to make additional adjustments to account for variation in AF time. With fixed focus, the above should be able to give you consistent intervals to within tens of milliseconds.

Of course, your interval also has to be longer than the maximum time the actual shot will take.
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Offline walterjwhite

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Re: accuracy of timing
« Reply #3 on: 28 / January / 2011, 10:37:35 »
I think I fixed the issue.  I used the get_tick_count found in another script to account for those differences.  I had already disabled the autofocus, so the only thing that would be dynamic would be the exposure time.  I should have been shooting a relatively stable scene.


Thanks,


Walter
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Offline walterjwhite

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Re: accuracy of timing
« Reply #4 on: 30 / January / 2011, 12:21:19 »
Hi,

This my revised script ... I am still having issues with every once and a while, it will miss a picture:



@title Intervalometer
i=2000

set_focus 4500
set_aflock 1

while 1 do
   a=get_tick_count
   shoot
   b=get_tick_count
   
   c=a - b + i
   
   if c < 0 then c = 0
   sleep c
wend



Walter
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Offline reyalp

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Re: accuracy of timing
« Reply #5 on: 30 / January / 2011, 14:57:14 »
What mode are you shooting in ? In some of the auto modes, the camera will refuse to shoot if it thinks are too wrong.

Are you shooting raw or DNG ?  If so, the saving time might exceed your 2 second interval.

Have you verified that the set_focus and set_aflock are doing what you expect ?
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Offline fudgey

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Re: accuracy of timing
« Reply #6 on: 30 / January / 2011, 15:07:01 »
Quote from: reyalp on 30 / January / 2011, 14:57:14
Are you shooting raw or DNG ?  If so, the saving time might exceed your 2 second interval.

Maybe in some circumstances exposure + focus + shoot + JPEG encoding + saving could exceed even 2 seconds (low light, JPEG scaling enabled, slow SD card, lots of photos on card, delay of creating a new DCIM subdirectory to SD card, ...).

And the obvious: did you disable photo review?
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