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Trying to Shoot every Three Seconds for 10 Minutes with Flash

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Offline lyod

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Trying to Shoot every Three Seconds for 10 Minutes with Flash
« on: 17 / March / 2015, 12:31:05 »
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I'm working on machine vision project with my SX260HS (firmware 101a, CHDK 1.3.0-4075) and I need some advice from the CHDK experts. My goal is to take a shot with medium flash every three seconds for 10 minutes.

I can use any intervalometer script to do this for up to ~20 images, but after the ~20th image the flash charge symbol starts blinking and the shot interval becomes long and sporadic. I opened the camera to probe the flash capacitor and found that the charge time (to ~320V) is always less than two seconds, even after 20 shots when the charge symbol blinks. If I quickly reboot the camera I can take another 20 images in three second intervals before the flash charge symbol blinks. This makes me think the canon firmware is limiting the number of flashes even if the system is able to handle more.

I tried doing a param dump during normal operation and when the charge symbol was blinking, but the only changes I see are in the frame count and the time of last frame. I also looked through event procedures but none jumped out at me as solutions.

One solution would be to reboot the camera every 30 seconds. I'd like to avoid this if possible as it would mean retracting the lens and flash every 30 seconds which leads to a ~10 second interval between shots.

I understand that doing this could damage the camera.

Does anyone have ideas for tricking the canon firmware so that the flash can fire every three seconds for 10 minutes?
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Offline waterwingz

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Re: Trying to Shoot every Three Seconds for 10 Minutes with Flash
« Reply #1 on: 17 / March / 2015, 13:56:50 »
If it's not the exact same number of images each time, then it seems likely the camera is slowing down due to some internal condition it is measuring.

Could it be a temperature issue?  Most Canon P&S cams monitor several internal temperatures.  If it is, then bypassing this may very well cause permanent damage.

You can use the CHDK OSD to monitor the know sensor readings while you run some test.
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Ported :   A1200    SD940   G10    Powershot N    G16
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Offline lyod

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Re: Trying to Shoot every Three Seconds for 10 Minutes with Flash
« Reply #2 on: 17 / March / 2015, 17:48:48 »
I just ran a test to see if it is the exact same number of images each time. In this test I turn the camera on, start the intervalometer, then when the flash charge symbol starts to blink I shut down and repeat. The number of flashes turns out to be deterministic:

Code: [Select]
reboot001.log
Image 0001 at time 17 h 8 m 36 s
Image 0002 at time 17 h 8 m 39 s
Image 0003 at time 17 h 8 m 41 s
Image 0004 at time 17 h 8 m 43 s
Image 0005 at time 17 h 8 m 45 s
Image 0006 at time 17 h 8 m 47 s
Image 0007 at time 17 h 8 m 49 s
Image 0008 at time 17 h 8 m 51 s
Image 0009 at time 17 h 8 m 53 s
Image 0010 at time 17 h 8 m 55 s
Image 0011 at time 17 h 8 m 57 s
Image 0012 at time 17 h 8 m 59 s
Image 0013 at time 17 h 9 m 1 s
Image 0014 at time 17 h 9 m 4 s
Image 0015 at time 17 h 9 m 6 s
Image 0016 at time 17 h 9 m 8 s
Image 0017 at time 17 h 9 m 10 s
Image 0018 at time 17 h 9 m 12 s
Image 0019 at time 17 h 9 m 14 s
Image 0020 at time 17 h 9 m 16 s

reboot002.log
Image 0001 at time 17 h 9 m 33 s
Image 0002 at time 17 h 9 m 35 s
Image 0003 at time 17 h 9 m 37 s
Image 0004 at time 17 h 9 m 39 s
...

reboot008.log
Image 0001 at time 17 h 15 m 26 s
Image 0002 at time 17 h 15 m 29 s
Image 0003 at time 17 h 15 m 31 s
Image 0004 at time 17 h 15 m 33 s
Image 0005 at time 17 h 15 m 35 s
Image 0006 at time 17 h 15 m 37 s
Image 0007 at time 17 h 15 m 39 s
Image 0008 at time 17 h 15 m 41 s
Image 0009 at time 17 h 15 m 43 s
Image 0010 at time 17 h 15 m 45 s
Image 0011 at time 17 h 15 m 47 s
Image 0012 at time 17 h 15 m 49 s
Image 0013 at time 17 h 15 m 51 s
Image 0014 at time 17 h 15 m 54 s
Image 0015 at time 17 h 15 m 56 s
Image 0016 at time 17 h 15 m 58 s
Image 0017 at time 17 h 16 m 0 s
Image 0018 at time 17 h 16 m 2 s
Image 0019 at time 17 h 16 m 4 s
Image 0020 at time 17 h 16 m 6 s


In each of the eight reboots 20 shots were fired before the limiting kicked in. Also you'll notice I'm using a two second interval in this test. I ran the same test with a three second interval and the results are the same (20 shots until the blinking charge light).
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Offline waterwingz

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Re: Trying to Shoot every Three Seconds for 10 Minutes with Flash
« Reply #3 on: 17 / March / 2015, 20:12:34 »
Quote from: lyod on 17 / March / 2015, 17:48:48
In each of the eight reboots 20 shots were fired before the limiting kicked in. Also you'll notice I'm using a two second interval in this test. I ran the same test with a three second interval and the results are the same (20 shots until the blinking charge light).
So the camera is clearly keeping count and slowing down.  Almost certainly to protect the hardware.

Did you try adding logging for the temperature sensor values to your script (as I essentially suggested)?   get_temperature(sensor_number)

It would be interesting to see how long the interval needs to be such that the camera does not slow down?  10 seconds?  30 ? 60?

Finally, what if you have the script take the 19th shot with the flash disabled? Does that reset it?

"Grasping at straws here" but I don't believe anyone is going to be able to provide you with a better definitive answer.
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Ported :   A1200    SD940   G10    Powershot N    G16
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Offline lyod

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Re: Trying to Shoot every Three Seconds for 10 Minutes with Flash
« Reply #4 on: 18 / March / 2015, 10:28:30 »
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Did you try adding logging for the temperature sensor values to your script (as I essentially suggested)?

I tried this but the temperature measurements don't seem to have any correlation with the flash limiting.

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It would be interesting to see how long the interval needs to be such that the camera does not slow down?  10 seconds?  30 ? 60?

Just ran some more tests at the medium flash setting. The minimum interval for flashing continuously is around 12 seconds. With an 11 second interval the flash charge symbol blinks after 20 shots. With a 12 second interval the flash charge symbol never blinks (tested through 51 shots).

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Finally, what if you have the script take the 19th shot with the flash disabled? Does that reset it?

I tried this manually and it didn't seem to help. I'll try doing this in a script.

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"Grasping at straws here" but I don't believe anyone is going to be able to provide you with a better definitive answer.

I understand this is a weird/silly/foolish request. I appreciate the help!
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Offline srsa_4c

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Re: Trying to Shoot every Three Seconds for 10 Minutes with Flash
« Reply #5 on: 18 / March / 2015, 10:43:51 »
Take a look at this. It's an old topic, but it might be a good starting point.
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