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Archive 2012 · For Noobs: What I learned today
  
 
morganb4
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p.1 #1 · p.1 #1 · For Noobs: What I learned today


OK So I generally don't have an issue with getting decent whites. Two reasons for this are I am persistent, tenacious and I am not above using photoshop + layers to fix corsslights when they get really mental.

What I learned today is that a scene lit with a low pressure sodium lamp effectively can not be white balanced. Some one here mentioned it a while ago and I am just reiterating that point.

If you are out and about and think you can rely on available light and you only sodium lights around, check. Do a quick custom WB and shoot a few tests. If the images make no sense then you may well be dealing with LP sodium.



Sep 23, 2012 at 01:45 AM
jcolman
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p.1 #2 · p.1 #2 · For Noobs: What I learned today


Sodium vapor lights are the work of Satan. The are evil, nasty lights.


Sep 23, 2012 at 02:00 AM
morganb4
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p.1 #3 · p.1 #3 · For Noobs: What I learned today


High pressure sodium is often mixed with a few other things like mercury and does have a spectrum associated with but LP just gives you a flat 598nm and thats your lot.

Edited on Sep 23, 2012 at 02:12 PM · View previous versions



Sep 23, 2012 at 02:33 AM
Ian Ivey
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p.1 #4 · p.1 #4 · For Noobs: What I learned today


OK So I generally don't have an issue with getting decent whites.

That's racist.

OR

Yeah, they all look alike to me, too. You shoot one, you've shot them all.

OR

And they say it's hard to get good help.


I've been watching too much Tosh.0



Sep 23, 2012 at 03:10 AM
morganb4
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p.1 #5 · p.1 #5 · For Noobs: What I learned today


Did I just get trolled?


Sep 23, 2012 at 03:45 AM
Ian Ivey
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p.1 #6 · p.1 #6 · For Noobs: What I learned today


Did I just get trolled?

NSFW: http://www.youtube.com/watch?v=4bAK8nWxZEY

If you have to ask....



Sep 23, 2012 at 03:47 AM
morganb4
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p.1 #7 · p.1 #7 · For Noobs: What I learned today





Sep 23, 2012 at 03:56 AM
ricardovaste
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p.1 #8 · p.1 #8 · For Noobs: What I learned today


Where do I find/avoid these evil lamps?


Sep 23, 2012 at 09:53 AM
tonyhart
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p.1 #9 · p.1 #9 · For Noobs: What I learned today


Can you give us more detail Benedict?


Sep 23, 2012 at 03:40 PM
morganb4
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p.1 #10 · p.1 #10 · For Noobs: What I learned today


Only my mother calls me Benedict, and thats when I've been really bad.

Well most street lamps are (I believe) high pressure but are mixed with a few other things and so you tend to get a bit of a spectrum (i.e. colour range).That means you will get a spectrum back from your subject i.e. colour.

With a low pressure lamp (often a deep orange colour), the output is a flat 598nm, single frequency. Therefore you will never get any other colour reflected back from your subject so you cant ever WB it properly.

If in doubt do some test shots and if accept that your shots are going to be in BW or have a brown ambient colour. I even found that BW conversions seemed harder than normal. Really this kind of lighting is conducive only to BW.



Sep 23, 2012 at 03:48 PM
 

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Ian Ivey
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p.1 #11 · p.1 #11 · For Noobs: What I learned today


Tony, the problem with sodium lighting is that it is nearly monochromatic, meaning it produces a peak of light output in the middle of the visible spectrum, but does not produce light waves across the visible spectrum. Most lighting you encounter (tungsten, fluorescent, sunlight, "white" LED) produces light waves across most of the visible spectrum, even though each kind emphasizes different parts of the spectrum. When you adjust white balance, you're simply compensating for the differences in emphasis.

Low-pressure sodium lighting peaks near, and just drops off after, the part of the visible spectrum to which the human eye is most sensitive (which is why that kind of light is efficient -- it doesn't waste energy producing a lot of infrared or ultraviolet light your eye can't use). But that means objects in that kind of light can't reflect the colors of light that simply aren't present.

So there's no white "balance" that can accommodate the absence of light colors necessary for accurate color representation.

Here's a reasonably good explanation of how low-pressure sodium light differs from other light sources.



Sep 23, 2012 at 03:51 PM
morganb4
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p.1 #12 · p.1 #12 · For Noobs: What I learned today


^Thats interesting, it makes the point that contrast is enhanced which explains why the BW conversions seemed harder to do. Thanks Ian.

Heres a particularly brutal example.







Sep 23, 2012 at 04:01 PM
Ian Ivey
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p.1 #13 · p.1 #13 · For Noobs: What I learned today


I even found that BW conversions seemed harder than normal.

Yes, black and white conversion of photos taken under low-pressure sodium lighting would be more challenging because contrast is skewed. Some colors that would normally reflect a medium luminance level reflect nearly no light at all (appearing black) or reflect very high levels of light (appearing near white or blown) because they are respectively far from or near to the peak light frequency of the lamp.

Black and white conversion can compensate for mixed-light-color environments (e.g., tungsten plus flash) where you can't white balance the entire image, but you still have fairly representative luminance levels across the image. That's because black and white is basically just a measure of the quantity of reflected light, regardless of color (simplifying, here). Thus you have contrast levels that are roughly as expected after converting a mixed-light image to black and white, even if the colors you started with were gaudy.

But low-pressure sodium lighting doesn't even produce appropriate contrast levels for accurate black-and-white imaging. It does produce a monochromatic picture (converted or not), but not in the way black and white film (or full-spectrum sensors converting to black and white) produces monochromatic images lit by full-spectrum light sources.

It may be easier to understand how it would look if you just shined a purple light on your subjects. Things at the other end of the spectrum would not reflect the right quantity (luminance) of light to produce the expected contrast level. For example, something that's bright orange might appear to be nearly black under a purple light.



Sep 23, 2012 at 04:06 PM
Ian Ivey
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p.1 #14 · p.1 #14 · For Noobs: What I learned today


^Thats interesting, it makes the point that contrast is enhanced

The article says contrast is enhanced, but it is talking about how the human eye interacts with that light. So it is correct from that view, but a camera sensor does not behave in quite the same way. Image contrast is more skewed than enhanced by LPS light, because the camera sensor is looking for the entire spectrum and does not have the same particular sensitivities the human eye has.

If contrast were merely "enhanced" from the sensor's perspective, then it should (arguably) be fairly easy to make a b&w conversion of LPS-lit images, simply by dialing down the contrast. But the problem is really that the luminance levels of objects in the image are just wrong under LPS light because some things that should reflect medium levels are too high or too low, some things that should reflect little light end up reflecting a lot, and some things that would reflect a lot of full-spectrum light are dimmer than they should be compared to the other objects in the image.

Luminance under LPS all depends on how close to the color of LPS light the object is.

The take-away, here, is that every photographer should have a good BB-gun handy to deal with this issue when necessary.



Sep 23, 2012 at 04:19 PM
morganb4
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p.1 #15 · p.1 #15 · For Noobs: What I learned today


someone should get a list together of all venues that are lit outside with LPS...


Sep 23, 2012 at 04:25 PM
zndr
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p.1 #16 · p.1 #16 · For Noobs: What I learned today


As just an FYI you have multiple kinds of light in that shot, and white balancing would best be done by hand with multiple layers, It's not impossible but this would be the same as having tungsten and daylight mixing. Your BG building has both downward (looks like halogen) and upward lighting of different typs plus you have the LPS lighting on the subjects which, is also a giant pain on it's own. And that light is reflecting off the windows and back out. the fact that it's so many lights is what makes the above shot hard, not that it's LPS. The LPS just makes it more harder...or something grammatically more correct than that.


Sep 24, 2012 at 07:20 PM
amonline
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p.1 #17 · p.1 #17 · For Noobs: What I learned today


jcolman wrote:
Sodium vapor lights are the work of Satan. The are evil, nasty lights.


I think Zack Arias refers to those as Satan's Acid. No kidding.



Sep 24, 2012 at 08:42 PM
Chris Beaumont
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p.1 #18 · p.1 #18 · For Noobs: What I learned today


Elephant in the room maybe?

Is that the colour they were to the eye??

I sometimes think we get so obsessed with perfect colour we ignore what colour things actually were.



Sep 24, 2012 at 08:53 PM
TTLKurtis
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p.1 #19 · p.1 #19 · For Noobs: What I learned today


Chris Beaumont wrote:
Elephant in the room maybe?

Is that the colour they were to the eye??

I sometimes think we get so obsessed with perfect colour we ignore what colour things actually were.


I don't think people care that much about what color it 'actually' is - it looks like hell. I'd be pissed if a photographer delivered images with color like that.



Sep 24, 2012 at 11:02 PM
morganb4
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p.1 #20 · p.1 #20 · For Noobs: What I learned today


I agree, it needs to look nice and he consistent.

For the record, just in case of any confusion, I did not submit images like that. I worked the hell out of them Nd git a good result. The shot posted is one where my flash didn't hit the wall behind me quite right/didn't fire.

Chris, i was using my own light but was expecting more latitude from the ambient light. Lights with the cast or a skew re looking thing but completely monochromatic is something else.


TTLKurtis wrote:
I don't think people care that much about what color it 'actually' is - it looks like hell. I'd be pissed if a photographer delivered images with color like that.




Sep 25, 2012 at 02:23 AM
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