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Lighting with home disco strobes


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Greetings all,

I am thinking about doing a night dream sequence outside using home disco strobe units with coloured gels. I would like to know if anyone has experience with this.

Some questions:

What is the relationship of of shutter angle vs. strobe speed?

What is the relationship of frame rate to strobe speed?

Any insights would be greatly appreciated.

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>What is the relationship of of shutter angle vs. strobe speed?

 

The flash duration is the "shutter speed" i.e very short.

 

>What is the relationship of frame rate to strobe speed?

 

With a 180 degree shutter you'll get ~ 1/2 the flashes on film.

 

10 flashes per second (often the max rate on commercial "theater" strobes) @ 24fps you'd get about 5 per second per unit.

 

What you see in a mirror reflex finder is exactly what you DON'T get on the film and versa vice......

 

> Any insights would be greatly appreciated.

 

The home units don't put out much light, not as bright as they "look"

 

You can stagger multiple units to get more flashes on the film.

 

With unsynced strobes you can run the risk of catching - "freezing" the shutter's edge, this may not matter to you/

 

-Sam

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Thanks Sam.

I don't exactly know what ".... "freezing" the shutter's edge" would look like.

Can you describe it?

Also these units have a potentiometer that's marked slow and fast. Any suggestions about slightly more accurate calibration so I can have a slightly more precise of the flash rate?

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Hi,

 

Freezing the shutter, as far as I can work out, refers to the extremely short duration of the xenon strobe occurring while the shutter is partially obscuring the frame, with the result that you get a strobe exposure over one part of the frame, and a hard line between that and the non-strobe exposure. I cautiously predict that it'd look a bit like a video monitor with a very severe sync fault.

 

Watch Alien. There's lots of strobe work towards the end where Sigourney Weaver is making her way to the escape shuttle. You can clearly see that the strobes are running at almost exactly 12Hz, meaning you get alternate-frame flashes about half the time, and nothing the other half. I recognise the type of strobe and, like almost all of them, they're a simple diac-breakdown trigger - once the thing's charged to a certain level it releases. It's possible but not really a practical retrofit to make these sync to things.

 

As for more precise control - there's probably syncable flash units out there, including those strobes that're intended for high speed shooting (someone remind me of the name.) There's also Dataflashes, which are strobes designed for DMX-512 control which are capable of a very wide range of effects and should be easily rentable. It is a coincidental characteristic of DMX-512 that it updates the entire range of addresses at exactly 48Hz, and with a bit of electronics it might be possible to sync that to the camera, then work out the delays required to have strobes hit exact frames. Bit of a development project, though.

 

Phil

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I think Phil pretty much answered it.

 

Of course you can go with a synced system like Unilux, but.... $$$$, worth it if you need it.

I think you'll be doing it by "feel" really - it can work OK. Run the camera w/o the mag to get a sense of what's happening at different rates.

 

Interesting idea on DMX Phil !

 

I do think there'd be some homework to do. Last time I used DataFlash-like units, (they were actually HyperFlash) there were some compatibilty issues between the controller and one head. Turned out to be easier to have a PA hit the buttons ! (find a PA who's an ace at text messaging :D

 

-Sam

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A vintage strobe that uses electrolytic capacitors instead of the polypropylene(?) power factor caps that most current strobes are using will give you a much longer flash. The ESR (equivalent series resistance) of electros is much higher, meaning they can't dump their whole charge anywhere near as fast, hence the longer flash.

Regarding the DMX idea - it would be far simpler to build a synced strobe from scratch than try to turn DMX into a useful timebase. Most lighting desks are smart enough that they will only transmit the last channel with data greater than zero, so the actual frame (DMX frame, not film frame) time is usually much shorter than all 512 channels.

However there are disco strobes with 'remote' or 'audio' trigger inputs, which are pretty easy to interface with. One more item on the ever growing to-do list is a 'gen-lockable' strobe sync-box.

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