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Catching a flash on two cameras simultaniously


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#1 Stephen Price

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Posted 08 December 2009 - 01:31 PM

Hello All,

I'm currently on a UK drama using two F35's. We had just done a shot where both cameras were shooting a scene while a sigle bright flash is triggered. We were finding only one camera would catch it at a time. The DoP was keen to get both cameras to capture the flash, retried it several times but to no avail.

Both cameras each had a lock it box, and were gen locked. We could not slow down the length of the flash, it was a fixed speed. I tried slightly adjusting the shutter angle on one of the cameras to see if that would catch it but it did not.

Every time one camera would catch it and the other would not. Is there any tricks to this? Presumably the F35 is no different to many other digital cameras in this sense. I guess it is to do with the syncing of both cameras.

Any suggestions?

Many Thanks

Steve Price
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UK
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#2 David Williams

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Posted 08 December 2009 - 04:16 PM

Shutter off might do it.
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#3 Stephen Price

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Posted 10 December 2009 - 07:40 AM

Unfortunatly, turning the shutter off is not an option as the correct motion for the action is critical.

Ant other thoughts?
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#4 Ed Sieb

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Posted 10 December 2009 - 09:33 AM

Sounds like one of the cameras is one field (1/2 frame) out of synch from the other. This may due to cable lengths affecting the propagation of gen lock signals to one or the other camera. Most studios would lock the cameras to the burst or synch gen via equal lengths of cable, or delay lines.

Can't think of any other reason.
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#5 Hal Smith

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Posted 10 December 2009 - 10:00 AM

Same make and model of lock box? If different there could be a phase difference between the two outputs. You'd never notice that sort of thing until trying to capture an instantaneous event on two cameras.
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#6 Stephen Price

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Posted 11 December 2009 - 04:18 AM

Hello,

Thanks for your replies.

Both cameras were using the new lock it box from Abient ACL 203. Designed specifically for a more accurate Tri Level sync. And all the cable were brand new and exactly the same length.

One important factor i did not mention before was, we where using both cameras with the SRW-1 deck split from the camera body. The lock it boxes were fitted to the deck and connected with Timecode and Genlock was connected to the ref in on the deck.

On reflection, the camera could no way benefit from the Genlock as in the mode we were shooting the two units are separate entities. Has any one experience with this? When separated in this way, should you still Genlock from the camera body?

Many Thanks
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#7 Chris Millar

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Posted 11 December 2009 - 05:43 AM

Out of interest does the phase on any camera come from the point at which you hit record, start up the camera, or from some other higher up the chain source (internal clock) ?

Depending on the answer to that you could just keep trying until dumb luck came about or maybe even never get any overlap in the exposures (exactly 180deg out of phase).
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#8 Stephen Price

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Posted 11 December 2009 - 08:45 AM

Out of interest does the phase on any camera come from the point at which you hit record, start up the camera, or from some other higher up the chain source (internal clock) ?


Thats a good question, i have always assumed that it would be from when the system powers up. Maybe that's not the case.

Anyone?
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#9 Stephen Price

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Posted 16 December 2009 - 03:59 AM

I spoke to my UK Sony contact yesterday. They confirmed that the sync of the camera generated internally begins during its startup. This is true for all sony cameras. When Gen Lock is connected, it automatically switches to being slaved off the master source and will switch back to its internal clock when disconnected.
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#10 Chris Millar

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Posted 16 December 2009 - 05:34 AM

I spoke to my UK Sony contact yesterday. They confirmed that the sync of the camera generated internally begins during its startup. This is true for all sony cameras. When Gen Lock is connected, it automatically switches to being slaved off the master source and will switch back to its internal clock when disconnected.


Righto - interesting - thanks for finding out...

I thought it could really be any of those options - I know my EX1 for instance has a 'always on' clock in the background that is used in the metadata for instance (actually thats an assumption) but now that you've confirmed it is put into phase at start up at least if you found you weren't getting much luck you could try switching on and off until you got a good overlap in the two exposures.

Hopeless with one off events though huh :rolleyes:
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