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4k HMI distance?


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#1 Brandon Rubesh

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Posted 26 March 2008 - 07:54 AM

Just a quick question that I'm sure some of you know right off the top of your heads. I'm going to be shooting a 4k HMI through the windows of a cafe. Going next week to scout the cafe and was thinking about the distance I need outside the cafe to place the light. I'd like a stop of around a 5.6 to an 8 inside the cafe. I know there's probably some sort of formula for this, but I'm not sure of what it is. Thanks for any advice.

- Brandon
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#2 Mike Lary

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Posted 26 March 2008 - 08:03 AM

Have you checked to see if there are photometric charts available for the light? I don't know what light you're using, but a quick search came up with this:
http://extranet.mole...page/6641-L.gif
You'd just need to convert the foot candles to f-stop with a chart from the ASC manual or elsewhere.
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#3 Brandon Rubesh

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Posted 26 March 2008 - 11:19 AM

I don't know exactly what light I will rent yet, but I was thinking a 4k HMI with some optional lenses. For the inside I would just have on hand kinos and smaller tungsten units for fill, eye lights, focus areas, etc. but I want the main source to be from the HMI placed outside. But thanks for the link, I'll check it out.

- Brandon
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#4 Brandon Rubesh

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Posted 26 March 2008 - 11:35 AM

Ok got it! for 50 ASA at an F8 I need around 400 footcandles, unless I'm mistaken. So with the different lens options that allows me a margin of between 25 and 150 ft outside the cafe. Thanks!

- Brandon
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#5 Kevin Zanit

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Posted 26 March 2008 - 11:45 AM

The 4K with lenses is a PAR, though many of the 4k PARs rent with a fresnel lens as well.

Though your photometric numbers may give you the stop you are looking for, don't forget that you need spread as well. You may have plenty of foot candles, but its in a very small spot.

Plan on needing to diffuse the light if you need it to spread and light a large space.
Posted Image
(those are 18k fresnels through opal)

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#6 Mike Simpson

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Posted 26 March 2008 - 11:13 PM

Maybe this should be a seperate subject but its somewhat related so Ill just ask. I was having a similar conversation dealing with a 4k thru a window yesterday, and we were trying to get the hardest light possible with a 4k fresnel.

The window was about 5ftx5ft, the actor about 10 ft away from the window, the wall another 10 feet from the actor.

So I asked for the light to be backed up and spotted in so it was hitting all of the window but not much more.

My question: The gaffer told me I should flood the light out to get the as hard as possible. This seemed counter intuitive to me, and Im having a hard time wrapping my head around it.

To me, it seems like I should spot the light in and back it up as much as I can while keeping the exposure good to get the hardest shadows. He claimed it should be as far away while full flood and maintaining good exposure.

Anyone else run into this before?

Edited by Mike Simpson, 26 March 2008 - 11:14 PM.

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#7 Hans Engstrom

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Posted 27 March 2008 - 03:50 AM

Maybe this should be a seperate subject but its somewhat related so Ill just ask. I was having a similar conversation dealing with a 4k thru a window yesterday, and we were trying to get the hardest light possible with a 4k fresnel.

The window was about 5ftx5ft, the actor about 10 ft away from the window, the wall another 10 feet from the actor.

So I asked for the light to be backed up and spotted in so it was hitting all of the window but not much more.

My question: The gaffer told me I should flood the light out to get the as hard as possible. This seemed counter intuitive to me, and Im having a hard time wrapping my head around it.

To me, it seems like I should spot the light in and back it up as much as I can while keeping the exposure good to get the hardest shadows. He claimed it should be as far away while full flood and maintaining good exposure.

Anyone else run into this before?


With a Fresnel you get harder shadows when its flooded. It´s because when it´s flooded all rays travel parallel and when it´s spotted they don´t and may cross each other creating fuzzy shadows.
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#8 Serge Teulon

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Posted 27 March 2008 - 09:37 AM

Ok got it! for 50 ASA at an F8 I need around 400 footcandles, unless I'm mistaken. So with the different lens options that allows me a margin of between 25 and 150 ft outside the cafe. Thanks!

- Brandon


Kodak tables show that 400fc = F4 on ASA 50 not F8

S
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#9 Mike Simpson

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Posted 27 March 2008 - 11:21 AM

With a Fresnel you get harder shadows when its flooded. It´s because when it´s flooded all rays travel parallel and when it´s spotted they don´t and may cross each other creating fuzzy shadows.


And that really makes a bigger difference than the extra distance you get from maintaining the same intensity by spotting and moving back?
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#10 Hans Engstrom

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Posted 27 March 2008 - 01:19 PM

And that really makes a bigger difference than the extra distance you get from maintaining the same intensity by spotting and moving back?


Yes it will. The extra distance will however be good to minimize the falloff but for sharp shadows I would go with flooding the fresnel.
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#11 Nor Domingo

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Posted 27 March 2008 - 07:20 PM

Yes it will. The extra distance will however be good to minimize the falloff but for sharp shadows I would go with flooding the fresnel.


Is that the same for a par, say a 4k arrisun, when flooded or is that only for fresnel lamps? Creating harder shadows, i mean.
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#12 Tebbe Schoeningh

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Posted 31 March 2008 - 02:10 AM

check out the photometric calculator on arri.com
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