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Current status of precision sync

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Offline waterwingz

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Re: Current status of precision sync
« Reply #10 on: 02 / May / 2015, 14:28:59 »
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Quote from: arsenix on 02 / May / 2015, 10:18:58
The only CRTs I have laying around are in my old digital oscilloscopes. I should be able to use the vertical scale on one of those to test sync.
This post explains pretty nicely how to do that : 
D20's, hall effect sensors and stereo-photography
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Offline arsenix

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Re: Current status of precision sync
« Reply #11 on: 02 / May / 2015, 17:25:36 »
In an unrelated incident I just smoked both of my functional cameras... and in swapping the mainboards one of the lens flex connects tore. One of those days! So sync testing will have to wait until I get a shipment of more camera guts.
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Offline mr.burns

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Re: Current status of precision sync
« Reply #12 on: 04 / May / 2015, 03:27:49 »
Hi,

I am thinking of a different way to measure sync for my stereo S110s, but don't know if it is reasonable.
I want to replace the CRT measuring way if possible.
Is there any way (may using a script) to switch on the AF LED after image was taken?

Then I  would put a photo transistor in front of each cam's AF LED and use my oscilloscope to measure the difference in time when both AF LEDs switch on.

Can / will this work?

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Offline waterwingz

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Re: Current status of precision sync
« Reply #13 on: 04 / May / 2015, 08:19:05 »
Quote from: mr.burns on 04 / May / 2015, 03:27:49
I am thinking of a different way to measure sync for my stereo S110s, but don't know if it is reasonable.
I want to replace the CRT measuring way if possible.
The link I posted above gives you away to do it using just your oscilloscope.   
  • Configure both cameras for USB remote operation with sync  - One Push switch, Normal control mode
  • Connect both cameras to a shared USB remote switch
  • Point both cameras at the screen of the oscilloscope
  • Attach your scope probe across the shared USB remote switch
  • Set the scope to trigger when the switch is released ( i.e. falling edge with a trigger threshold around 2.5V)
  • Set the horizontal sweep to 10 msec/division  (you may want to tweak this later
  • Press the switch, hold for two seconds, release the switch
  • Download the resulting two images and observe in each photo where the scopes beam was when the shutter opened
  • The difference in the two positions is the camera's "sync accuracy"

Quote
Is there any way (may using a script) to switch on the AF LED after image was taken? Then I  would put a photo transistor in front of each cam's AF LED and use my oscilloscope to measure the difference in time when both AF LEDs switch on.
While this can be made to work (best done as a hack to CHDK C code) it will not be very accurate as you will essentially be measuring variations in sync and variation in the time it takes to turn on the LED.  There is no way to know how much of the total measured values to assign to each delay.
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Offline mr.burns

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Re: Current status of precision sync
« Reply #14 on: 05 / May / 2015, 01:45:52 »
Hi waterwingz,

thanks for reply. But I doubt that it will work wit my digital oscilloscope (HAMEG HMO1022).
This uses an LCD screen and there is no beam I can track.

Do you think it can/will work?
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Offline waterwingz

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Re: Current status of precision sync
« Reply #15 on: 05 / May / 2015, 08:42:05 »
Quote from: mr.burns on 05 / May / 2015, 01:45:52
thanks for reply. But I doubt that it will work wit my digital oscilloscope (HAMEG HMO1022).
This uses an LCD screen and there is no beam I can track. Do you think it can/will work?
You could still try it but as you suspect, the LCD update rate and the image refresh rate will probably not be fast enough for it to work. I guess there are still some things my very old analog oscilloscope can do better than a fancy digital scope. 

Which I guess leaves you with only a few options :
  • Find an old CRT monitor (thrift shop? computer repair place? 2nd hand store?) and use the SDM sync test
  • Beg / borrow an analog scope for a couple of days
  • Build something like I did here :  testing sync among more cameras.  It actually worked pretty well - especially once I expanded it to 10 high brightness LED's
  • Build some sort of rotating target with alternate black & white stripe and spin that target very quickly.  (electric drill?).  Then photograph with the two cameras sync'd and measure the difference in the resulting images.  If you know the rotational speed the a little math will give you the sync error.

It's never easy, is it ?
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Offline mr.burns

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Re: Current status of precision sync
« Reply #16 on: 07 / May / 2015, 10:41:34 »
Hi waterwingz,

no it's never easy ;-)

What about this one:

Create a small circuit of a resistor of 1K, phototransistor, power supply and DSO digital oscilliscope.
(see attached image)

Then switch on the flash on both S110s (lowest power of flash will be enough).
Then take a photo using USB switch, sync enabled.
Then both cameras will take a photo and fire the flash. The DSO should detect two peaks from 5V to 0V, one from the flash of the first cam, the other one from the 2nd cam.
The closer both peaks are together (on the x-axis of the DSO) the better the cams are synced.
The sync delay can be calculated by the time difference of both peaks.

Can/will that work?
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Offline mr.burns

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Re: Current status of precision sync
« Reply #17 on: 11 / May / 2015, 02:12:28 »
Hi,

I still need some help on this please - many thanks!
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