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will I need an IR filter for this kind of shoot?


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#1 Jamie Metzger

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Posted 13 April 2009 - 03:21 PM

http://www.hemmy.net...-kanazawa-city/

We are building a 12x12 room with 3/4 inch plexi holding 1-2 inches of water above us. The performers will be underneath the plexi, no one will be on it. We will be silking the sun, and using a 6K to augment.

I'm unsure if I will need an IR filter (or an 85) because of all of these variables.

Any ideas would be great.

Thank you

Jamie
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#2 John Sprung

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Posted 13 April 2009 - 03:55 PM

With only 2" of water, the color shift to blue-bluegreen should be way too small to worry about. It takes a few feet to become significant.

The big concern here is that 2" of water on a 12 x 12 ft area is close to 1500 pounds. Add the plexi and it's like walking around under a car. The water should keep you safe from localized heating, but be real careful about dropping anything onto the plexi and starting a progressive failure from a small impact point. Use a laser level to get the plexi dead on first.




-- J.S.
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#3 Jamie Metzger

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Posted 13 April 2009 - 03:59 PM

With only 2" of water, the color shift to blue-bluegreen should be way too small to worry about. It takes a few feet to become significant.

The big concern here is that 2" of water on a 12 x 12 ft area is close to 1500 pounds. Add the plexi and it's like walking around under a car. The water should keep you safe from localized heating, but be real careful about dropping anything onto the plexi and starting a progressive failure from a small impact point. Use a laser level to get the plexi dead on first.




-- J.S.



Are you talking about getting a small crack in it, like a windshield, and it spreading during the shoot? Interesting point.

Did you address the IR filter need?
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#4 Serge Teulon

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Posted 13 April 2009 - 04:09 PM

Hey Jamie,

I think he did with the comment of ".....color shift to blue-green should be way too small to worry about."

I'm also feeling a bit apprehensive as I have a shoot with the red soon but from what I perceive from previous posts, the red tends to have a lot of noise in the blue channel....
The general consensus I'm getting is that the IR filter should always be implemented.

As for the 85 that would only come in use if you shoot with tungsten lights. As the cmos chip in the red is daylight balanced.

If I'm wrong, please, someone, correct me.
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#5 Jamie Metzger

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Posted 13 April 2009 - 04:15 PM

Hey Jamie,

I think he did with the comment of ".....color shift to blue-green should be way too small to worry about."

I'm also feeling a bit apprehensive as I have a shoot with the red soon but from what I perceive from previous posts, the red tends to have a lot of noise in the blue channel....
The general consensus I'm getting is that the IR filter should always be implemented.

As for the 85 that would only come in use if you shoot with tungsten lights. As the cmos chip in the red is daylight balanced.

If I'm wrong, please, someone, correct me.


I understand that the RED is 5000K, but I'm thinking that there will be an abundance of blue for this shoot, and I would like to be prepared. I'll have one regardless. I was on an outdoor cloudy shoot with the red, and there was tons of IR and we didn't have a filter. I had the kelvin up to 10,000K and it still wasn't warm enough.

Jamie
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#6 Serge Teulon

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Posted 13 April 2009 - 04:32 PM

If you figure that there will be tons of blue then I would definitely get an IR filter.

Good luck with it and it would be great to know how it worked out for you.
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#7 John Sprung

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Posted 13 April 2009 - 05:36 PM

Are you talking about getting a small crack in it, like a windshield, and it spreading during the shoot?


Yes, and plexi being flexible, it would start to sag at the cracks, more water would flow to the low area, increasing the load on the weak points. Then it could suddenly let go like the World Trade Center. The water would merely be unpleasant, but broken 3/4" plexi with the force of that water behind it could hurt people. You need a special effects crew who really know their s--t.

As for the IR filter, it never hurts. It protects you from the unknown. But this being heavy in blue rather than red, it's less likely to be an issue. With the Red, you see what you have, so you know what the IR's doing, if anything.

An 85 filter may be way more than you need. Given the low sensitivity of silicon to blue, you're better off getting as much blue as you can to the chip, and taking it down in post. Filtering too much optically and cranking blue up in post will get you into noise trouble.




-- J.S.
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Rig Wheels Passport

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Aerial Filmworks

Glidecam

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Metropolis Post

rebotnix Technologies

Technodolly

FJS International, LLC

Ritter Battery

The Slider