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Vivek Venkatraman

Shafts of Light with 5 KW Fresnels

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Hello,

 

I know this is a topic that has been brought up time and again on this forum but the past posts have not solved my problem.

 

So I have a project to shoot where I need to create a shaft of light coming in from a window.

 

EQUIPMENT I HAVE ACESS TO

 

1 -Tungsten Fresnels [2KW, 5 KW ,1 KW and below]

2 - Big cardboard reflectors

3 - Small Mirrors, big mirrors if need me

4 - Dust particles

 

DETAILS OF LOCATION/SHOOT

 

1 - It is day outside the location and inside the location.

2 - Currently the weather is over cast

3 - There are a couple of windows from where I can add the light

4 - Distance between window to subject is 5 -8 Feet

5 - Distance between window to light creating beam can be anywhere from 2 feet to 10 feet

 

OTHER DETAILS

 

1 - I will be giving a light bounce to fill the room [aperture of around 2 iso 400 maybe] I will make sure that the ambience does not kill the beams

2 - There will be a practical on the table as part of set dressing.

 

QUESTIONS

 

Is the distance enough for me to get visible rays of light ?

Is the fact that it is day outside [some of which might leak into the room] going to dilute the ray ? I can work around this narrowing the openings in the window. I have this liberty.

Should the light be full soft and focused by cutters ? or should it be spotty ?I can also open the fresnel of my 2 KW or 5 KW allowing more spread in the light which makes it easier to shape

How does distance affect my beam ?

Is bouncing it off a mirror better ?

 

Your suggestions and thoughts please.

 

 

 

 

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I would prefer the look of dust particles over smoke for my scene ? Wont dust particles [lots of them] do the trick ?

 

You have to consider what is safe for your actors and crew to breathe, as well as what is manageable in terms of maintaining a consistent level of smoke or haze.

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Fog in a Can, anyone?

post-64976-0-78533400-1439743872_thumb.jpg

 

:rolleyes:

 

(no, i don't work for Fantasy FX)

Use with bare naked bulbs. No diffusion necessary. Absolutely no bounce or reflected light. 1K or 10K doesn't matter. Hard light gets you hard shafts.

On the other hand, soft light gets you thick blanket of fog.

As for dust, I wouldn't sprinkle that on actors or all over the room. Sprinkle it three feet from the lens and have the operator (and other crew, i.e. dust wrangler) wear a mask, with a basin out of frame to catch that dust. An "eye light" nearest the front of the lens can reflect most of the dust particle without killing your asthmathics.

Edited by Larry DeGala

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A DF-50 Hazer would be ideal. Fog in a Can works for small spaces, otherwise you'll need a lot of cans and lots of people to spray them simultaneously.

 

If you want a strong beam (like 4 stops over) relative to the rest of the room then you may need more powerful lights, especially if you are going to lose 2 stops by adding Full CTB on the 5K to match the existing daylight ambience. A more powerful light further away would give you more a parallel beam and less falloff in exposure - it would look more like real sunlight and less like a spot light. I would look into getting a 4K HMI Par at least.

 

Also consider that a beam of light will be more visible against a dark background, so if you keep the ambience lower then you can get away with a less powerful beam.

 

Use a photometrics calculator to figure out how much light you need: http://calc.arri.de/calculator. ISO 400 @ f/2 1/48sec would be 12 footcandles (fc) required for key exposure. 4 stops over key would be 200fc.

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I would do a mix of a very light even haze plus whatever dust particles you want to float in the air, you could try "effects dirt", which is a sort of powder (Fuller's Earth used to be used until it was deemed unsafe to breathe). You can also try some finely chopped feathers too. Just keep in mind that if you can see particles floating in the air, you want to limit how much of it the actors and crew have to breathe it (the crew can at least wear masks).

 

It's very hard to create an actual solid shaft of light through dust that is not horrible to breathe, and just faint bits of dust in otherwise clean air is harder to see in wide shots, it's not really a shaft effect. You also need a more projected intense light source to really pick up actual dust in the air well (a Source-4 Leko with a narrow lens works well, as does a Xenon, or a narrow spot ParCan). This is why I suggest that you need a mix of haze and dust, the smoke haze to create a base shaft that you can then float dust particles in.

 

As for a 5K fresnel, it all depends on what it is competing with. Outside a window at night coming in at a backlit angle, you'd get a nice beam even in full flood, but have it mix with bright ambient daylight and it might not look intense enough, it would be a fainter shaft. On an overcast day, it might be the right amount of light or you may need to spot it in less.

 

A shaft of light is visible due to the combination of its intensity and the angle relative to the camera coming through something in the air to catch the light, a backlit angle being the most visible.

 

What's good about powerful projected beam lights or bigger fresnels or open face units is that you get a shaft of parallel rays -- with a spotted-in light you may get a stronger beam but it will be shaped differently than sunlight, it will have a hotter center and the dimmer edge will spread more. If you are trying to create the effect of hard sunlight, it helps to have bigger units farther away so that the beam is sharper and spreads less quickly. Other than a big unit farther away, the only thing similar is a small unit with a lens that projected a focused beam like a Leko-style light. But then you won't have the area of coverage that a big unit further away will create, it won't fill a window edge-to-edge. Now that's not always necessary if you can imagine the sun being cut off from filling the window by some partial obstruction like a tree or other building. This is why it sometimes works to put three or four Lekos with narrow lenses outside a window all coming in at the same angle and direction, so that the multiple beams are parallel. Then it looks like one ray of sunlight being broken up by tree branches or the window frame, etc.

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Corn starch is biologically safer than talcum powder (remembering the time students clapped chalkboard erasers, eek!). When using any flour, do not have an open light source (such as burning candle or torch) nearby. Fine flour misted in the air will ignite, and anything flammable in that flour mist will also burst into flames (actors). Be safe and have fun!

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Larry, telling people that things are dangerous, while simultaneously suggesting their use is kinda stupid. Any fine powder suspended in air will ignite under a naked flame or hot lamp. There are a great many substances that we no longer use; cracked oil and Fuller's earth being just two. Water based and Glycol based haze and smoke is accepted as safe, and non explosive, corrosive or carcinogenic. There's a reason why they are used. Let's not make wild suggestions that could have serious consequences.

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Larry, telling people that things are dangerous, while simultaneously suggesting their use is kinda stupid. Let's not make wild suggestions that could have serious consequences.

Stuart Brereton, not sure where "be safe" was lost in translation. it is better to be forewarned than to be forlorned. Safety first.

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Being safe would be not suggesting the use of Corn Starch, or any other flour.

 

Corn starch is biologically safer

But still explosive.

 

When using any flour, do not have an open light source (such as burning candle or torch) nearby.

 

Don't ever use flour!

 

These substances are banned on every professional set in the western world. Why you would choose to suggest them is beyond me.

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On 8/17/2015 at 4:19 AM, David Mullen ASC said:

I would do a mix of a very light even haze plus whatever dust particles you want to float in the air, you could try "effects dirt", which is a sort of powder (Fuller's Earth used to be used until it was deemed unsafe to breathe). You can also try some finely chopped feathers too. Just keep in mind that if you can see particles floating in the air, you want to limit how much of it the actors and crew have to breathe it (the crew can at least wear masks).

 

It's very hard to create an actual solid shaft of light through dust that is not horrible to breathe, and just faint bits of dust in otherwise clean air is harder to see in wide shots, it's not really a shaft effect. You also need a more projected intense light source to really pick up actual dust in the air well (a Source-4 Leko with a narrow lens works well, as does a Xenon, or a narrow spot ParCan). This is why I suggest that you need a mix of haze and dust, the smoke haze to create a base shaft that you can then float dust particles in.

 

As for a 5K fresnel, it all depends on what it is competing with. Outside a window at night coming in at a backlit angle, you'd get a nice beam even in full flood, but have it mix with bright ambient daylight and it might not look intense enough, it would be a fainter shaft. On an overcast day, it might be the right amount of light or you may need to spot it in less.

 

A shaft of light is visible due to the combination of its intensity and the angle relative to the camera coming through something in the air to catch the light, a backlit angle being the most visible.

 

What's good about powerful projected beam lights or bigger fresnels or open face units is that you get a shaft of parallel rays -- with a spotted-in light you may get a stronger beam but it will be shaped differently than sunlight, it will have a hotter center and the dimmer edge will spread more. If you are trying to create the effect of hard sunlight, it helps to have bigger units farther away so that the beam is sharper and spreads less quickly. Other than a big unit farther away, the only thing similar is a small unit with a lens that projected a focused beam like a Leko-style light. But then you won't have the area of coverage that a big unit further away will create, it won't fill a window edge-to-edge. Now that's not always necessary if you can imagine the sun being cut off from filling the window by some partial obstruction like a tree or other building. This is why it sometimes works to put three or four Lekos with narrow lenses outside a window all coming in at the same angle and direction, so that the multiple beams are parallel. Then it looks like one ray of sunlight being broken up by tree branches or the window frame, etc.

Hi David,

Does a source 4 leko flicker if I shoot high speed? I'm looking at speeds of 100 and 150.

I'm looking to create 'pillars' of light for a music video, so need sharp focused, parallel beams (or as close to that as possible). Considered some stage lights as well, but haven't yet found one that will work with high speed and won't seriously overexpose the actor, should s/he happen to catch the light.  

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