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Diffusing HMI for maximum throw


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#1 Toni Vucic

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Posted 14 May 2018 - 03:14 PM

Hello everyone

 

I'll be gaffing a night interior shot on 200T film in a few weeks. The idea is to have a very blue moonlight through the window(s), and have the tungsten sources inside register as warm. It's a low budget short so there will only be one moonlight fixture (and a bunch of dimmed tungsten inside)

 

DoP doesn't want the hard light from a pure HMI. I assume we will want to be able to shoot out the windows.

 

My ideal fixture would be a daylight balanced maxibrute, which gives a window-sized source and a fairly focused beam. But I'd need more than full CTB to get the color we want, which is a real waste of energy.

 

Is there a type of diffusion I can use with a 1.8kW Arrimax HMI that maintains the light direction and (somewhat) intensity while increasing the source area? My experience with stuff like Lee 250 and 216 is that it goes everywhere, and throw is lost. A grid on standard diffusion isn't the solution either, as a lot of light is lost when it gets absorbed by the grid. I don't mind doing double diffusion like in a softbox as long as it somewhat keeps its direction while getting softer.

 

Thanks in advance  :)


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#2 David Mullen ASC

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Posted 14 May 2018 - 04:49 PM

Its just a compromise between lighter diffusion that softens less and heavier diffusion that softens more. You might consider using a frame (like 6x6 or 8x8) of either Half Soft Frost (similar to Opal but not noisy in wind) or 1/4 Grid Cloth (more like 250). You can get a soft egg crate light control grid for the frame.

They do make some of the grid cloths dyed blue but I think it would be easier to just add blue gel to the light if uncorrected HMI daylight isnt blue enough.
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#3 Albion Hockney

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Posted 14 May 2018 - 11:18 PM

I'm confused why you are worried about the "light direction" when it is an interior shoot. Since you are placing the light outside of windows spill/source size shouldn't be a big problem as the windows will control most of the spill. I think you need to separate two things: How diffused the source should be (IE the shadow and wrap quality of the light) and Spread of the beam of light. 

 

The spread of light can be controlled in various ways, with flags and egg crates etc. It does get harder to control with a more diffused (IE larger) source, but if you have windows involved and a bit of distance between the source and subject you should be able to use flags to control the source off of what you don't want it hitting w/o much of a problem. 

 

So I think all you really need to do is decide how soft you want the moonlight and then decide on the right density and size of diffusion to obtain that (of course along the way make sure you are not loosing too much light to obtain the stop the DP wants at 200 ISO). If you think Lee 250 is too strong try 251 or if you want bigger then 4x4 half soft frost like David mentioned might be a good pick.  

 

As for light loss/throw from the diffusion generally you can account for that by using a big enough light. To get a ball park I generally just combine the photometrics of the light you want to use ( http://calc.arri.de/calculator ) w/ the light loss of the diffusion ( http://www.leefilter...usion-list.html


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#4 Toni Vucic

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Posted 15 May 2018 - 03:10 AM

Thank you for the replies David and Albion.

 

The reason I'm concerned about light direction is because I want to maintain the intensity of the beam, so I don't have to rent a bigger more expensive light.

If I need to use a diffusion that takes two stops to get the same size source as a maxibrute, I might as well use a maxibrute and gell it full CTB.

 

Thank you for that Lee filters comparison. 264 Tough Spun 3/8 seems to have an interesting characteristic where it increases the source area a lot while only taking one stop of light. Lee claims in the description of all the Spuns that they leave the beam intact.

9UvlWyu.jpg

 

 

464 Quiet Quarter Grid Cloth has a similar effect.

AJOxNDc.jpg

 

If we compare to the Half Soft Frost, the beam size seems to barely have increased, while it takes a stop and a half of light..

d8XhQ4n.jpg

 

Thoughts?


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#5 David Mullen ASC

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Posted 15 May 2018 - 09:14 AM

If you want some spread to the beam, then it looks like the 1/4 Grid Cloth is your answer.

 

You could also try putting four ARRI SkyPanels together for semi-soft moonlight effect.


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#6 Albion Hockney

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Posted 15 May 2018 - 09:26 AM

 

If I need to use a diffusion that takes two stops to get the same size source as a maxibrute, I might as well use a maxibrute and gell it full CTB.

 

A couple things about your Maxi brute idea. 1 is that you will need to rent a generator of considerable size to run a light like that which would cost I'm sure more then a larger light. (I'd think it would cost less to run an M40 off a putt putt then run a maxi off a trailer mounted generator, not just because of the rental, but also crew). The cheapest thing would probably be two M18's and a putt putt.

 

The other thing is the size of the source. I might be wrong about this, but I have never known anyone to choose a maxi brute because of the source size. Generally it is backed off so far away the separate source's unify into a single beam or it is put through diffusion. The intention generally isn't to get a softer source - but I don't have much experience with that so maybe there is a softening quality - I'd just be worried about having multiple staggered shadows. 

 

Lastly the Lee diffusion guide is far from perfect, I wouldn't worry too much about those little pictures. Although I will agree soft frost  is not the most efficient diffuser. It has a nice quality though. 


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#7 Adrian Sierkowski

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Posted 15 May 2018 - 09:37 AM

Before going Maxi-Brute I might even consider going 2x 4K Soft-Lights with perhaps 1/2 CTB on them and saving the diff. (this assuming one couldn't get a skypanel or gemini).


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#8 David Mullen ASC

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Posted 15 May 2018 - 02:53 PM

If you're really set on using a Maxibrute, I suppose you could find some old FAY globes with dichroics in them for a bluer color base... But you could just use multiple HMI's and fill a diffusion frame too if you want a softer light.


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#9 Toni Vucic

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Posted 15 May 2018 - 05:15 PM

Thank you for all the thoughtfull replies.

Power isn't an issue on this location. It's an old hospital and the caretaker has arranged extra circuits for films there before. But of course it's nice to not have to ask for that favor.

 

Good point about the brute Albion, I might have needed some light diffusion to blend the bulbs. But we've decided against the brute due to the hassle of moving it and powering it.

As far as I know, soft-lights are not available in Norway sadly.

 

Very interesting point about the dichronic FAY globes David. I forgot they existed. Maybe one of the rental houses still has them, I'll keep it in mind. My angle now is going for HMI.

 

Skypanels are out of our budget.

 

My ideal solution now if the budget permits it, is a 6x6 frame of 1/4 silent grid cloth, with two 1800w Arrimax HMIs through it.

My next best is the two HMIs through a 1x1m 1/4 silent grid frame each attached to the light (save money on easylifts and cloth woooo)

Last choice is just one HMI through a 1x1m frame.

 

I also fired off an email to Lee to ask for their thoughts and got this back:

Thank you for your email, I would suggest the 464 as you mentioned in your email.


Richard McKitty - Business Development Manager


Edited by Toni Vucic, 15 May 2018 - 05:20 PM.

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#10 Josh S Wilkinson

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Posted 16 May 2018 - 03:04 PM

One of the thing ive done thats worked pretty well is using an M18 into a 8x8 silver lame with a little haze, the silver even cools the light out a little more.
Stays very directional.

https://1drv.ms/u/s!...cpa92CnWvFGRBrw

Edited by Josh S Wilkinson, 16 May 2018 - 03:09 PM.

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