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high speed with strobes?


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#1 Scott Weatherford

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Posted 20 November 2006 - 02:27 PM

Im shooting a music video next week and i really would like to do some lighting with strobes and high speed simultaneously. Ive read some things about Unilux and other systems, but as far as my gear is concerned, im shooting on an old Arri 16 SR capable of approx 80fps, and just an old strobe light with variable speeds, although the speeds are not denoted on the actual strobe light. I did a camera test and the footage didnt come out that great, but considering i just winged it i knew it wouldnt be good.
Does anyone have any good suggestions about how to light with strobes for 16mm 24fps and higher? im not married to the idea but it will provide a very appealing aspect to the video. I fear that i dont have the proper tools and gear of high enough quality to acheive this! Help!
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#2 Michael Nash

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Posted 21 November 2006 - 03:29 AM

I'm not really sure what you're asking -- are you trying to create random strobing, and just want to know how to expose for it, or are you trying to synch the strobes to the camera?

If you have a light meter with a flash function, you can meter the strobes and set your exposure accordingly. Without a way to synch the flash to the camera's shutter, you're going to get an irregular pattern of exposed strobes. Some flashes will be missed by the shutter, others will be only partly exposed, and some will be completely captured on film. If you see a flash through the viewfinder while rolling, then you've missed at least part of that flash on the film.
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#3 Scott Weatherford

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Posted 21 November 2006 - 12:44 PM

Right, the viewfinder issue makes sense, and metering hasnt proven an issue yet (ive metered my strobes in various situations and have gotten correct exposure for my camera tests). My question was more about syncing and if theres any way to get around the irregularity of the strobe and shutter. I was told by someone that if i keep the strobe rate low, then it would work better, but what about higher speeds, 40fps, 70 fps? Seems like if the shutter is moving faster, i can have the strobe going a bit faster as well.

the problem with my camera test was when the flash goes off when the shutter is only half in or out, when its covering half of the gate, and you get that chopped look where only the top or bottom of the frame is exposed.... THATS what im trying to get around, and i dont know if theres a way.
thanks
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#4 Nick Mulder

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Posted 21 November 2006 - 05:12 PM

Right, the viewfinder issue makes sense, and metering hasnt proven an issue yet (ive metered my strobes in various situations and have gotten correct exposure for my camera tests). My question was more about syncing and if theres any way to get around the irregularity of the strobe and shutter. I was told by someone that if i keep the strobe rate low, then it would work better, but what about higher speeds, 40fps, 70 fps? Seems like if the shutter is moving faster, i can have the strobe going a bit faster as well.

the problem with my camera test was when the flash goes off when the shutter is only half in or out, when its covering half of the gate, and you get that chopped look where only the top or bottom of the frame is exposed.... THATS what im trying to get around, and i dont know if theres a way.
thanks


heh, we did exactly the same thing on a recent music vid

I dont know about the Arris but find some sort of 1:1 shaft on camera and use it to trigger the strobe (something that turns in sympathy with the shutter)...

I've done it with a bolex but the strobe unit I had was so unpredictable in its 'time it takes to fire after being triggered' spec that is was still a mess at 25fps - it was pretty good/quick to trigger at lower speeds though, so I got 5 strobes and built a circuit that fired them in sequence 25/5 = relative 5fps for each strobe

The larger your shutter angle the more room you have to play with and with no other lighting the stobe in effect becomes the shutter angle and you can shoot any speed you want without having to change aperture - great for speed ramps...

with a bolex we had the prism so viewfinding wasnt an issue - with a rotating mirror I would just double the strobe rate so you get a flash when the shutter is closed also (ie. use a 2:1 shaft or put two 'switches' on your 1:1) - you could attempt to make that flash a bit more mellow than the exposure flash so charge times would be shorter, thats bit heavier electronics though...

We just guessed exposure... a bit risky but it came out fine

watch out for epileptics

I should also add:

As for 80fps - using this method youd need 80/5 = 16 of the same spec strobes that we used (fun!) - though its probably time to look into dedicated units for hire
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