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Sodium Vapor


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#1 Nadav Hekselman

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Posted 17 June 2009 - 09:06 AM

(I accidentally posted this topic also in the Cinematographer section)

Hey everyone,

I'm about to shoot a short on August with a lot of night exteriors. Most of the locations are streets in Tel-Aviv which are usually lit with the famous sodium vapor lights (the low pressure yellow-orange ones).

I'll probably be shooting on EX3 or F900 and looking for the best way to shoot those lights. I want to keep their yellowish quality but in a nice and natural way. According to some tests I did I fear a simple WB wont be enough and some camera or post manipulation are needed. any advice on camera settings? WB? post work?

Also I need some advice with gel configuration for matching 3200k light to the sodium ones. A configuration that will be nice for skin tone.

Any other advice on handling those vapors will be appreciated.

Thanks.

Edited by Nadav Hekselman, 17 June 2009 - 09:06 AM.

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#2 David Mullen ASC

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Posted 17 June 2009 - 10:15 AM

Sodium Vapors have missing wavelengths so they cannot be fully corrected -- all you end up with is a muddy, desaturated image if you try. Plus if you try and white balance to a color temp much lower than 3200K, you are already pushing the blue channel quite heavily. At the most, you could try just adding a little coldness to take out some orange. But white balancing under the sodium lights isn't really going to work well, I'd try putting some 1/4 CTO on a tungsten light pointed at a white card and white balancing to that -- that would add a little blue into the sodium color but not cancel it completely.

As for gels, there are lots of combinations people try. Rosco just created two new gels for this purpose: Industrial Vapor, which is an ugly brown-green gel that supposedly matches real sodium, and Urban Vapor, which is an orangey-yellow gel that looks like most people's impression of sodium vapor without as much green. But you could also try various gel combinations, like Full CTS + 1/4 Plus Green, Apricot, etc.
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#3 Nadav Hekselman

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Posted 17 June 2009 - 02:31 PM

Sodium Vapors have missing wavelengths so they cannot be fully corrected -- all you end up with is a muddy, desaturated image if you try. Plus if you try and white balance to a color temp much lower than 3200K, you are already pushing the blue channel quite heavily. At the most, you could try just adding a little coldness to take out some orange. But white balancing under the sodium lights isn't really going to work well, I'd try putting some 1/4 CTO on a tungsten light pointed at a white card and white balancing to that -- that would add a little blue into the sodium color but not cancel it completely.

As for gels, there are lots of combinations people try. Rosco just created two new gels for this purpose: Industrial Vapor, which is an ugly brown-green gel that supposedly matches real sodium, and Urban Vapor, which is an orangey-yellow gel that looks like most people's impression of sodium vapor without as much green. But you could also try various gel combinations, like Full CTS + 1/4 Plus Green, Apricot, etc.


Thank you David for the quick reply.

I'm actually trying to find a way to keep the sodium yellowish color but in a nice way. Any advice doing that?
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#4 David Mullen ASC

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Posted 17 June 2009 - 07:03 PM

Thank you David for the quick reply.

I'm actually trying to find a way to keep the sodium yellowish color but in a nice way. Any advice doing that?


"Nice way" is rather subjective, isn't it? Shoot some test footage with sodium vapor lights and time it in post to see what degree of color shift you want to employ. Then decide if you want to add that shift in post, or with camera filters, or by fooling the white balance, playing with other levels in the camera.
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#5 M Joel W

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Posted 17 June 2009 - 07:16 PM

Low pressure sodium lights emit two visually undifferentiable wavelengths, and are capable of rendering only one color: deep orange. You can't use gels to change their color because they emit only one; you can only add or subtract how much "ugly orange" you have. (Black body sources like incandescent lights and carbon arcs emit a broad spectrum of colors in a curve that is centered around their nominal color temperature; thus tungsten lamps' color temperature can be changed nicely with gels.) Every gel on a low pressure sodium light will work like an ND gel and will not alter color temperature. The same goes for filters, so I wouldn't advise using an 82 filter or whatever; it will just work like an ND filter. White balance is some sort of algorithm magic, so it might do some good, but it might result in something weird.

Newer streetlights (high pressure sodium) render color much better, but they are still not great. If you can use an area with these you'll be much better off. I think there's an article in AC where Rodrigo Prieto discusses how he dealt with street lights when shooting 8 Mile, but I haven't read that article, and I'm not sure if he was dealing with low pressure sodium, high pressure sodium, or mercury vapor. For what it's worth, I've noticed that the EX1 is good with discharge lamps, but I doubt anything can make low pressure sodium look good.

David's one of the most knowledgeable people on this board and I would take his advice. Find a white balance (maybe around 2700ยบ) that looks okay and use your scene files to decrease saturation if that helps. Post work can change the tint of your footage but it can't introduce colors that were never there. Shoot some test footage to make sure this doesn't look terrible or introduce lots of video noise; the lower your WB the noisier your footage will generally be. If you plan to light your wide shots, use tungsten lights with gels of your choosing to get a similar looking color temperature, or dim your tungsten lights until they look more orange.

For close ups, you can flag off the discharge lamps and use softer, prettier colors on your talent. Maybe use 1/2 CTS or something. Just test to make sure everything matches okay and nothing gets too noisy.

Edited by Matthew Wauhkonen, 17 June 2009 - 07:20 PM.

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#6 Nadav Hekselman

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Posted 18 June 2009 - 01:13 AM

I'll go do some more tests, aimed for post. I'll post them here for review when they are worthy of attention.


Thank you all for your inputs.
I
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