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Keying From Outside A Window

HMI 18K Lighting from window daylight interior

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#1 Jonathan Taylor

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Posted 12 March 2017 - 09:35 PM

I'm curious on what kind of output would be necessary to key from a light outside a window into a small (10ft x 12ft) room for a daylight interior setup. This is assuming no direct sunlight or night. Do I need a 12/18K or can I use something like an M90, M40, or even something of lower output?


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#2 David Mullen ASC

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Posted 12 March 2017 - 11:21 PM

Depends on so many factors, do you want a hard sunlight effect + soft skylight (or is the skylight natural, available light) or do you want a soft light?  What ASA rating, what f-stop do you want to shoot at, how big is the window, etc. Time of day? But I'd hazard a guess and say that a room that small probably doesn't have a huge window and you can do most anything you want with a 6K or 4K HMI, soft or hard, or maybe even just two M18's through a diffusion frame. You might need nothing at all if there is enough natural daylight.  But likely you don't need a 12/18K.


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#3 Brian Drysdale

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Posted 13 March 2017 - 03:18 AM

I've done it with a 2.5K HMI though diffusion over the window and it gave a reasonable overcast day look inside. It wasn't planned, but we had to shot a day interior at night, instead of shooting during the day (it was a low budget job).


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#4 Jonathan Taylor

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Posted 13 March 2017 - 05:21 PM

Depends on so many factors, do you want a hard sunlight effect + soft skylight (or is the skylight natural, available light) or do you want a soft light?  What ASA rating, what f-stop do you want to shoot at, how big is the window, etc. Time of day? But I'd hazard a guess and say that a room that small probably doesn't have a huge window and you can do most anything you want with a 6K or 4K HMI, soft or hard, or maybe even just two M18's through a diffusion frame. You might need nothing at all if there is enough natural daylight.  But likely you don't need a 12/18K.

 

Thanks David! I'm looking for more of a hard sunlight effect keying the talent (with maybe 1/4 grid) rather than a soft light key- although I may push it through shears. I'd probably shoot 800 ASA at a T2.0 to T2.5 range. Window is just your typical 2.5x5ft household window. Probably daytime with no direct sunlight to the window, just skylight. I'll link to an example of what I'm looking for. https://vimeo.com/121040557 The bedroom scene in the beginning is similar to what I'd like to achieve. (Credit to Steve Annis as DP for the piece)


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#5 Albion Hockney

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Posted 13 March 2017 - 05:46 PM

Bigger is always better I think - but you might even get away with an M18 for that if you need too. I would try to get an M40 Though.

 

The powerade spot for sure is using some diffusion - since the window isn't very big so even a strong diffusion will give you some beam shape and shadow quality.

 

If this is your biggest setup though save the budget and the big genny - get a putt putt and an M40 and you will be solid.


Edited by Albion Hockney, 13 March 2017 - 05:47 PM.

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#6 Adrian Sierkowski

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Posted 13 March 2017 - 05:55 PM

with today's higher iso cameras (basing around 800 which is kinda insane when i recall 500T being "insanely fast!") you can often get away with a very mobile combo of a M40 and 6500 honda-- so long as you don't need too much audio. If you do, though, really a 6K Par might be cheaper to rent than an M40 and once you run the distro for the tow plant you may find you're much more mobile and able to really get lights easily where you need them (assuming you have a good BBE).


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#7 Guy Holt

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Posted 22 March 2017 - 07:57 PM

... you can often get away with a very mobile combo of a M40 and 6500 honda-- so long as you don't need too much audio.

 

It is no longer true that Honda EU6500s make too much noise to record clean audio.  With the right equipment and planning it is possible to get clean audio tracks.

 

Even the super quiet Honda Inverter generators have the problem that by the time you move them far enough off set that you don't hear them you have significant line loss. To the problem of line loss, you have the added problem that as you add load, the voltage drops on portable generators (it is not uncommon for a generator to drop 5-10 volts under full load.) The combination of voltage drop on the generator and line loss on a long cable run can cause voltage to drop to the point where HMI and Kino ballasts cut out unexpectedly or won't strike at all. For these reasons, portable gas generators are typically operated too close to set where they are picked up on audio tracks. The trick to recording clean audio with a Honda EU6500is is to use a 240V-to-120V step down transformer, like our 60A Full Power Transformer/Distro, that has a slight voltage boost built into it, which enables you to operate the generator at a distance without suffering from voltage drop.

 

60A_Transformer-Distro_Honda_WebPS.jpg

Our 60A Full Power Transformer/Distro provides 7500 Watts of power in a single 120v circuit from the Honda EU6500is Generator or the new Honda EU7000is Generator 

 

To record sync sound without picking up any generator noise, all you need is 200'- 300' of extension cable between the generator and set. This is usually enough cable to place the generator around the corner of a building, or to run it out of a van or truck - which is usually all the additional blimping you need with these generators. A heavy-duty 250V twist-lock cable runs between the generator and the Transformer/Distro, which eliminates multiple long cable runs to the generator and eliminates the severe voltage drop you would have using standard electrical cords. And, to assure full line level (120V) on set, our Full Power Transformer/Distros are designed to compensate for the unavoidable line loss you will have over an extended cable run. 

 

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"Select" Models allow you to adjust for line-loss to maintain 120V on set

 

Our standard Transformer/Distro is designed to boost the voltage on the load side (secondary) of the transformer by 5 percent. For instance, if you were to plug the Transformer/Distro directly into a generator running with no load and feed the supply side (primary) of the transformer with the generator's 240V output, you will get 126 Volts out on the secondary side where you would plug in lights. We have designed this slight boost into our standard Transformer/Distro to compensate for the line loss that is unavoidable over a long cable run, and the voltage drop on the generator under load. Our "Select" model of Transformer/Distros, enables you to adjust the amount of voltage boost in two 5% steps. This enables you to maintain full line level (120Vs) regardless if the supply voltage has dropped to 228V, or even 216V, from line loss and load running on the generator.

 

A good example of how our Transformer/Distro makes it possible to record clean audio tracks even under the worst of conditions is the indie short "Toothbrush." In this story of mistaken identity produced by Guymanly Productions, a pivotal scene takes place in the middle of a near vacant parking lot of an all night convenience store.

 

GM_Title_Page_Sm.jpg

 

With no building or other sound barrier within a reasonable distance to block the sound of the generator, Gaffer Aaron MacLaughlin had no recourse but to put it behind their grip truck as far from set as possible. As you can see from the photos below, he ran 300' of twist-lock extension cable from the generator to our Transformer/Distro hidden behind a newspaper box. From the Transformer/Distro he then ran 200' of 6/3 Bates Extension to set where he broke out to 20A Edison receptacles using a 60A snack box. While running the generator near full capacity with a lighting package that consisted of three 1200W HMI Pars and two 1k Baby Quartz Fresnels, he experienced no appreciable voltage drop on set even after a 500' cable run because our Select Transformer/Distro was able to compensate for both the line loss of the cable and voltage drop of the generator under near full load. 

 

GM_MontageSm.jpg

Left: Scene in parking lot. Center: Transformer/Distro hidden behind newspaper box (set 200' in distance.) Right: Generator baffled by truck (Transformer/Distro 300' in distance.)

 

This example shows how the variable boost of our Select Transformer/Distros, not only enables you to place the generator further from set where you won't hear it, but also assures that the supply voltage on the secondary side of the transformer does not drop too low. By comparison, had Aaron run 500' of standard 14 Awg electrical cord he would have experienced a line loss alone of 24.5V. With that severe a voltage drop, his HMI ballasts would probably have cut out from low voltage as he added additional loads on the generator. Without the line-loss compensation of our Transformer/Distros, he would have had to move the generator closer to set where it would be picked up on the audio tracks.

 

For more detailed information on line loss, I would suggest you read an article I wrote on the use of portable generators in motion picture production. The article is available at www.screenlightandgrip.com/html/emailnewsletter_generators.html.

 

Guy Holt, Gaffer, ScreenLight & Grip, Lighting Rental & Sales in Boston

 


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Also tagged with one or more of these keywords: HMI, 18K, Lighting from window, daylight interior


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