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Light for sun beam effect: 2,500k HMI fresnel?


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#1 Tomas Koolhaas

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Posted 07 July 2006 - 12:58 AM

Hi Everyone,
I was just wondering people's thoughts on this: I am shooting 500T in various small rooms with windows on a ground floor, the director wants the room to be quite un-lit except for shafts/beams of hot sunlight coming through the windows, obviously I need to smoke the rooms to achieve this, but I am calculating that I will need around 300/400+ footcandles of light to sufficiently over-expose the beams coming in to get them "Hot" looking enough the light will probably be between 10/15ft from the subject. The Budget is very tight, For lights and power, so I was thinking of using a 2,500K HMI fresnel (that should give me the right amount of foot candles), which is only $170 per day, but I was wondering if this light would work well for the shaft affect seeing as the lense would make it less of a sharp "Beam". I've never used this light for this effect before so....
Has anyone used this light or one similarly priced (please no-one suggest Xenons!-$$$) for this effect???? Any thoughts would be appreciated.
Cheers.
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#2 Michael Nash

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Posted 07 July 2006 - 02:04 AM

I'd have to break out the Harry Box book to look up the exact footcandles, but in general for this kind of effect I'd use nothing less than a 6K HMI. With a fresnel you can get a really hot, narrow beam with a soft shadow (full spot), or a hard shadow with a bean that's significantly less bright (full flood). A 4K HMI par can be pretty darned punchy too.

With a 2500 HMI you're going to need a genny and some distro anyway.
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#3 Matt Workman

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Posted 09 July 2006 - 09:38 PM

Heh, when I got my 1200w HMI fresnel I though I could pull off an effect like that. Not quite. <_<

What is the industry standard fog machine? I would like to start experimenting with that effect.

How do you know how many FC you need to overexpose? I hardly use the FC rating, but I'd like to know.

Wouldn't a PAR be better suited for this effect over a Fresnel anyway?
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#4 Michael Nash

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Posted 10 July 2006 - 12:11 AM

Heh, when I got my 1200w HMI fresnel I though I could pull off an effect like that. Not quite. <_<

What is the industry standard fog machine? I would like to start experimenting with that effect.

How do you know how many FC you need to overexpose? I hardly use the FC rating, but I'd like to know.

Wouldn't a PAR be better suited for this effect over a Fresnel anyway?


There are some other threads around here about fog machines. For a general "haze" with good hang time, the DF-50 is very common.

The amount of overexposure for a shaft of sunlight totally depends on taste. For one thing, the amount of smoke, angle of the beam, and the darkness of the background it's framed against will all affect the visibility of the beam. As a point of reference though, I've always thought that sunlight coming through a window needs to be about three stops over (incident exposure) to look convincing, IF you're exposing for indirect or ambient light in the room. This is for film, not video; video takes less overexposure to look "hot." But if your subject is lit or partially lit by the shaft of light, you might choose to expose closer to the beam and effectively underexpose your interior. So it's all relative. Footcandles are only a measure of light and don't tell the whole story. The conditions of the room, framing of the shot, and film stock or video camera will all influence how bright you may choose to make a shaft of sunlight.

A par is very effective and giving a strong, focused shaft of light, but it's also diffuse within that beam and doesn't throw a very crisp shadow (like sunlight often does). Fresnels on the other hand can give a pretty sharp shadow in full flood, but you're spreading the light across a larger area and as a result don't get as much "heat."
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#5 chris kempinski

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Posted 10 July 2006 - 04:24 AM

my suggestion,
if you can only do it with the 2500. Take out the lens and full spot. You will gain about another stop.
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#6 Alex Wuijts

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Posted 10 July 2006 - 09:52 AM

my suggestion,
if you can only do it with the 2500. Take out the lens and full spot. You will gain about another stop.


you should never take of the lens of an HMI lamp because of danger of UV radiation burns and retinal burns.
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#7 Bob Hayes

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Posted 10 July 2006 - 10:28 AM

I usually choose to go with Pars because they are smaller and have more punch. A 2.5K HMI light might just be enough. Jordan Cronenweth did some fun lighting on a film called ?Cutter?s Way?. He lit some of the interiors using arcs outside the windows and white cards on the floor.

Don't pull the lens on an HMI!
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#8 Matt Workman

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Posted 10 July 2006 - 10:39 AM

My HMI's wouldn't strike if you pulled out the lens, most have a protection mechanism.

Doesn't the lens focus the light more anyway?
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#9 Rupe Whiteman

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Posted 10 July 2006 - 06:06 PM

A 2k xenon will give you a good strong shaft of sunlight in a smoked up average room (uk room that is!)...

- there's a good example of this in the 'Reflections' book from the asc...

- in general the bigger the source the better the shaft and the more control you'll have in terms of flagging and light shaping...

Rupe W

endeavour to persevere...
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#10 Miljan

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Posted 10 July 2006 - 08:35 PM

My HMI's wouldn't strike if you pulled out the lens, most have a protection mechanism.

Doesn't the lens focus the light more anyway?



Lens has a uv protection coating, no?
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#11 Tomas Koolhaas

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Posted 11 July 2006 - 12:03 AM

Heh, when I got my 1200w HMI fresnel I though I could pull off an effect like that. Not quite. <_<

What is the industry standard fog machine? I would like to start experimenting with that effect.

How do you know how many FC you need to overexpose? I hardly use the FC rating, but I'd like to know.

Wouldn't a PAR be better suited for this effect over a Fresnel anyway?


Hi,
Thanks for the responses, as M.Nash pointed out F/C are just a starting point, I hardly ever use them on set, but if you need a very specific effect (sun beam) and don't have the budget to just get a bunch of big lights, it helps to know roughly how many footcandles of light you need in order to get the right light. Im terms of exposure Micheal is right in that it varies on the angle background etc.. but I arrived at around 300/400f/c because I am shooting 500T and figured I would expose at around a 2.8 so in order to over expose the "Sun light" about 3/4 stops I would need around an 8/11 which on 500 you need around 300/400f/c of light on the subject to achieve (this is just roughly, as we said before there are many other factors and on-set it will no-doubt have to be tweeked, but in general for figuring out what kind of lights you need f/c can be very useful as arough guide).
Regarding Pars, I agree with micheal again, they often have softer shadows especially around the edges of the beam. Ideally I would just get a big Tungsten fresnel for this (20k) on full flood but we lack the funds for that so hopefully the 2,500k HMI will work out. Does anyone know if one type of fog machine or fogging liquid disperses more evenly and linggers (sp?) in the air longer (I really dont want people to notice that the room is smoked I just want enough that the beams are apparent).
Cheers.

Edited by Tomas Haas, 11 July 2006 - 12:04 AM.

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#12 Fredrik Backar FSF

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Posted 11 July 2006 - 03:37 AM

Trivia: The Norwegian queen and many others got retinal burns during a television show due to a broken lens on a fres.
C ya:-)
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#13 chris kempinski

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Posted 11 July 2006 - 01:59 PM

Super good to know
Thanks
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#14 Tomas Koolhaas

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Posted 11 July 2006 - 02:12 PM

Hi,
Frederik Bakkar, your music videos are excellent man!!!! not really relevent to this thread but still....respect!
Cheers.
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#15 Michael Nash

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Posted 11 July 2006 - 10:40 PM

Does anyone know if one type of fog machine or fogging liquid disperses more evenly and linggers (sp?) in the air longer (I really dont want people to notice that the room is smoked I just want enough that the beams are apparent).
Cheers.


There have been several threads here about foggers, some within the last year.

A "hazer" such as the DF-50 is ideal for what you want. The haze has good hang time if the room is sealed, and never gets too dense. "Party foggers" on the other hand put out dense billowy clouds that don't hang very long.
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Wooden Camera

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Glidecam

Media Blackout - Custom Cables and AKS

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