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beams of light


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#1 Christian Tanner

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Posted 23 May 2006 - 03:50 PM

hey guys!

i´m planing to use "visible light rays", "beams of light" as part of my lighting strategy for a shoot coming up.

i had just one or two goes at that before. and i can´t say i was entierly happy with the result.
there are actually just those three things i apply to get my light visible...:

smoke of course
backlight or at least cross.
the harder (and stronger) the better.

obviously you might think. that´s why i was wondering if anyone could give me advice in how to handle that tricky bit of lighting.
for instance - how strong should my lightsource preferably be? (a geni would stretch the budget - so, running 2.5k hmi´s on the normal hosehold sockets 13amp sockets would be ideal...).
also - i noticed that there is a certain angle a hard light is especially visible. that angle seems to be extremely tight. correct?
and last but not least - is there a trick i can check on how the beam of light is going to show on screen?

many thanx in advance guys!
cary
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#2 Michael Nash

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Posted 23 May 2006 - 06:07 PM

The one thing you left out is that the beam needs to viewed against a dark background. Even the brightest beam won't show up against white; and it takes very little to show up against black.

With more haze, a darker background, and a brighter light you can bring the beam angle more lateral. Shafts that are completely perpendicular to camera are done all the time.

How strong the light should be depends entirely on the light levels you're shooting at and how bright you want the shaft to appear. Just factor in that the farther away the unit, the more straight or narrow the beam becomes (which means the light has to be brighter for the same exposure).

Your eye is really the best judge to decide how the beam will look on film. You can attempt to spot meter it, but that can be tricky when the BG is busy and the haze very faint. Just go by eye.

You're not going to run a 2.5K HMI off a 15 amp circuit, though. 2.5's draw over 20 amps@110v and often have a 60a Bates coming off the ballast. For that reason the 1200W Par is the most common HMI to run off house power.
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#3 Christian Tanner

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Posted 24 May 2006 - 08:59 AM

thanx michael!

i´m shooting in the u.k. - at 220Volts. (or is it 230? - i'm confused... :) usualy they're on 16amp fuses. so i guess that explains why i was able to run 2.5ks so far.

anyways: should i use par lights? or the usual fresnel?

plus: the tricky thing is, that i shoot on location - not studio. meaning i got some sunlight coming in as well. luckily, i don't see windows in shot. would it make sense to build some kind of a "tent" with black cloth (hope you know what i mean) to get i darker - in order to cope with the 2.5ks?

...how much more expensive are stronger hmi's anyways?

over all - would you say it's feasible at all to do beams of light with 2.5k? or should i abandon the idea in the first place?

question after question...
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#4 Tim O'Connor

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Posted 24 May 2006 - 10:31 AM

The 1200w HMI pars are great because they come with different lenses so you can get a beam with real
punch to it or, with another lens and perhaps some diffusion to your liking, come a lot closer to a fresnel
effect with the same light. Plus you can plug them into the wall and they put out more light than some
bigger units that would require a generaator or tie-in.
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#5 Chris Cooke

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Posted 24 May 2006 - 01:24 PM

Should i use par lights? or the usual fresnel?

Use a narrow spot par. It'll output more light per watt and you can get a tighter beam.
The best option is to use a Xenon. It's an arc light that is very efficient and creates a high intensity parallel beam. Very expensive though.

plus: the tricky thing is, that i shoot on location - not studio. meaning i got some sunlight coming in as well. luckily, i don't see windows in shot. would it make sense to build some kind of a "tent" with black cloth (hope you know what i mean) to get i darker - in order to cope with the 2.5ks?

Yes. Otherwise, your blacks will get milky similar to flashing the negative. It's hard enough getting rich blacks when using smoke without other unwanted light entering the frame.

...how much more expensive are stronger hmi's anyways?
HMI's are 3 to 4 times stronger than tungsten units of the same type.

over all - would you say it's feasible at all to do beams of light with 2.5k? or should i abandon the idea in the first place?

2.5k is plenty of light depending on what your exposure will be and what other light is in the frame. I've created nice shafts of light against a black background with only a 500w narrow spot tungsten par.
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#6 Dominik Muench

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Posted 24 May 2006 - 01:50 PM

i recently used that on a music video shoot, if you have budget restrictions and cant rent xenons. go to a stage lighting company and get yourself a spot follower or chaser.

they have an adjustable spot size and a 2000W light gives you a lot of punch and a very defined ray of light.
also, with a 2000W light you dont need an extra generator, you can run it of a normal 220V circuit. they also have those little flip in frames at the front where you can place different gels, so color temperature isnt too much of an issue.

what i discovered was, that once we had our set smoked up for the light ray, the smoke reflected quite a lot of light and made the ambient light level on set rise a fair bit, i was surprised how bright it got.

Edited by Dmuench, 24 May 2006 - 01:54 PM.

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#7 Dominik Muench

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Posted 24 May 2006 - 02:10 PM

here are three samples of lightrays created with that stage follower:

http://www.hereticarts.com/blood1.jpg
http://www.hereticarts.com/blood2.jpg
http://www.hereticarts.com/blood3.jpg

sorry for the lowres images, i captured them from a small preview quicktime file, but im sure you'll get the idea :)
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#8 Michael Nash

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Posted 24 May 2006 - 04:42 PM

Everyone's replies are right on.

The only distinction I would make is that a fresnel unit on full flood will usually give you a sharper edge to shadows in the beam, but at the huge expense of output. A 1200W par with no lens will give you incredible punch, but a very narrow beam with "sloppy" edges (not sharp shadows). You'll have to decide how bright the beam needs to be, how much area it needs to cover, and how much visible "spread" of the beam you can accept for the shot (real sunlight shafts have paralell edges and don't "spread," if that's what you're trying to create).

You're right about the 220V thing; I didn't realize you were overseas.
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#9 Dominik Muench

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Posted 24 May 2006 - 04:51 PM

Michael: with the stage light i used, you were able to focus the edge of the beam and make it really sharp, no matter what the diameter of the beam was. the light had some sort of two lens system infront of the bulb which you could move back n forth.
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#10 Michael Nash

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Posted 24 May 2006 - 05:17 PM

Michael: with the stage light i used, you were able to focus the edge of the beam and make it really sharp, no matter what the diameter of the beam was. the light had some sort of two lens system infront of the bulb which you could move back n forth.


You're right. I was answering the par vs. fresnel question, but I probably should have included the ellipsoidals you mentioned as well.

Ellipsoidal units (like follow spots and source 4's) use a lens system to focus the beam very sharply. You get very high output from the source, but at the expense of a relatively narrow beam angle.

But if Cary is trying to balance to daylight, I don't think a 2k follow spot would be bright enough after color correction. Certainly not as bright as a 1.2 or 2.5 HMI.
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#11 Dominik Muench

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Posted 24 May 2006 - 05:22 PM

But if Cary is trying to balance to daylight, I don't think a 2k follow spot would be bright enough after color correction. Certainly not as bright as a 1.2 or 2.5 HMI.



yep, that could be the problem, i think the source 4s go up to 2500W only
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#12 Michael Nash

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Posted 24 May 2006 - 06:06 PM

I don't think actual Source 4 ellipsoidals go above 750W tungsten. But there are follow spots up to 2K tungsten; above that you go to either HMI or xenon.

While we're at it there are other kinds of "beam projector" options, including a 1.2 HMI followspot. And Mole makes a projector lens assembly for some of their fresnels (that slides right into the barn door bracket), but you REALLY lose a lot of light that way.
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#13 Christian Tanner

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Posted 25 May 2006 - 06:17 PM

thanx guys! that helped a lot - just changed my order to 2.5k pars...

beleive it or not - but i was told (and i believe that source word for word...) that i could use a 4k bulp in a 2.5k hmi - and still run it on 230v (in the uk) mains. well - i guess at least worth a try...

so, again - thanx guys - i let you know how it went.

cary
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#14 Michael Nash

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Posted 25 May 2006 - 10:53 PM

beleive it or not - but i was told (and i believe that source word for word...) that i could use a 4k bulp in a 2.5k hmi - and still run it on 230v (in the uk) mains. well - i guess at least worth a try...


There are units that can be globed either 2.5 or 4K, and of course it runs off the same voltage (that doesn't change), but that doesn't mean it draws the same amperage. To be honest I don't know exactly how the switchable ballasts work in terms of current draw. But I wouldn't expect to get more wattage (4k) out of the same voltage (220) without a higher amperage. Volts x amps = watts.

Check the amperage on your 4K unit before you plan on plugging it into a 16 amp circuit...
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#15 Christian Tanner

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Posted 26 May 2006 - 07:31 PM

....so...
what about that "little experiment" would go wrong - i was just wondering.
would the bulp just blow? or just the fuse right? and if so - would the rental house probably charge me for that (not treat it as a "normal" case of a burnt out bulp etc.)?
hmm...
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#16 Michael Nash

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Posted 26 May 2006 - 08:19 PM

....so...
what about that "little experiment" would go wrong - i was just wondering.


You'd just trip the house's circuit breaker (or blow the fuse, which would have be replaced). No big deal, but you wouldn't get the shaft of light for your film, either. ;)

It wouldn't cause any damage to the light or ballast. It just wouldn't be receiving enough amps to startup, or keep running if it did.
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Visual Products

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Technodolly

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Aerial Filmworks

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Glidecam

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Media Blackout - Custom Cables and AKS

Rig Wheels Passport

Broadcast Solutions Inc

Tai Audio