APOD: Ash and Lightning Above an Icelandic... (2010 Apr 19)
Re: APOD: Ash and Lightning Above an Icelandic... (2010 Apr
Gravity waves in Ash Cloud!!!
http://rapidfire.sci.gsfc.nasa.gov/real ... 0.250m.jpg
http://rapidfire.sci.gsfc.nasa.gov/real ... 0.250m.jpg
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Re: APOD: Ash and Lightning Above an Icelandic... (2010 Apr
Artifact of photography.DennyMo wrote:The question everyone I've shown the picture to is "Why is the lightning purple?" Any good answers to that one for me? Artifact of photography, spectral emissions of the lightning affected by the composition of the ash, other?
http://wvlightning.com/faqw10.shtml wrote:
Lightning photographs: The hue of lightning channels in photographs is usually a function of the type of film, camera, exposure and/or recording media used. The same lightning channel can appear blue, purple, red or orange depending on the type of film, length of exposure, and other factors. Slide film is more likely to produce a more purple/blue image, while print film tends to give lightning a more yellow/orange tint. >>
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Re: APOD: Ash and Lightning Above an Icelandic... (2010 Apr
Your reference to different emulsions producing different colors isn't very relevant to a digital image like this. In fact, lightning ionizes nitrogen, which results in the purple color seen here. The main lightning path is saturated, making it appear nearly white. Less bright paths show as a combination of the blue-white thermal continuum and the purple output of ionized nitrogen. The color of lightning can be further modified by scattering processes, depending on the amount of dust, rain, or hail in the air. This lightning appears to be in fairly clear air.neufer wrote:Artifact of photography.
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Re: APOD: Ash and Lightning Above an Icelandic... (2010 Apr
A closed mouth gathers no foot.
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Re: APOD: Ash and Lightning Above an Icelandic... (2010 Apr
Thanks for the above link - great photos!!!!
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Re: APOD: Ash and Lightning Above an Icelandic... (2010 Apr
Is this a 3D picture?Roundup wrote:Gravity waves in Ash Cloud!!!
http://rapidfire.sci.gsfc.nasa.gov/real ... 0.250m.jpg
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Re: APOD: Ash and Lightning Above an Icelandic... (2010 Apr
It wasn't clear to me that it was originally a digital photo.Chris Peterson wrote:Your reference to different emulsions producing different colors isn't very relevant to a digital image like this. In fact, lightning ionizes nitrogen, which results in the purple color seen here. The main lightning path is saturated, making it appear nearly white. Less bright paths show as a combination of the blue-white thermal continuum and the purple output of ionized nitrogen. The color of lightning can be further modified by scattering processes, depending on the amount of dust, rain, or hail in the air. This lightning appears to be in fairly clear air.neufer wrote:Artifact of photography.
In any event, this link claims that the nitrogen factor generates a distinctive blue-white color:
http://www.webexhibits.org/causesofcolor/4.html wrote:
<<Lightning is visible as a flash of light because of both incandescence (due to its high temperature it glows blue-white) and luminescence (excitation of nitrogen gas in the atmosphere). Nitrogen, the dominant gas in the atmosphere, is excited by this strong flow of energy, its electrons moving to higher energy states. The distinctive blue-white color of lightning is caused by light emitted as the electrons drop back to their original energy states.>>
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Re: APOD: Ash and Lightning Above an Icelandic... (2010 Apr
Well, aside from the fact that this is 2010, nobody uses film anymore, and if they did there are only a couple of color emulsions even available... you could always look at the EXIF header, which identifies the camera as a Fuji FinePix S3 Pro.neufer wrote:It wasn't clear to me that it was originally a digital photo.
It's wrong. The blue white color is from the blackbody continuum. Ionized nitrogen is very much purple.In any event, this link claims that the nitrogen factor generates a distinctive blue-white color:
![Image](http://z.about.com/d/chemistry/1/G/4/8/1/nitrogen-glow.jpg)
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Re: APOD: Ash and Lightning Above an Icelandic... (2010 Apr
: has the urge to make popcorn :
A closed mouth gathers no foot.
Re: APOD: Ash and Lightning Above an Icelandic... (2010 Apr
Thanks. I hoped it was somthing being ionized, but I didn't know which what it was.Chris Peterson wrote:Ionized nitrogen is very much purple.
Re: APOD: Ash and Lightning Above an Icelandic... (2010 Apr
Don't know about purple lightning. What amazes me is the lateral red hot ejecta above and below the lightning dendrite nearest the ash cloud. It appears to have a time lapse photo signature that is shorter than the star tracks. How could you photograph star tracks from a moving plane anyway? Camera would have had to been stationary, right? ![Neutral :|](./images/smilies/icon_neutral.gif)
![Neutral :|](./images/smilies/icon_neutral.gif)
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Re: APOD: Ash and Lightning Above an Icelandic... (2010 Apr
That is a vial of ultrapure nitrogen with the purple's red componentChris Peterson wrote:It's wrong. The blue white color is from the blackbody continuum. Ionized nitrogen is very much purple.neufer wrote:In any event, this link claims that the nitrogen factor generates a distinctive blue-white color:
presumably coming from nitrogen returning to it's ground state.
Lightning excited air at one atmosphere might (or might not) be a different situation\
(; it certainly isn't as clear cut to me as you make it out).
http://en.wikipedia.org/wiki/Aurora_%28astronomy%29 wrote: Auroral colors:
<<nitrogen emissions: Blue or red.
Blue if the atom regains an electron after it has been ionized.
Red if returning to ground state from an excited state.
oxygen emissions: Green or brownish-red, depending on the amount of energy absorbed.>>
http://en.wikipedia.org/wiki/Nitrogen wrote:
<<Nitrogen also makes a contribution to visible air glow from the Earth's upper atmosphere, through electron impact excitation followed by emission. This visible blue air glow (seen in the polar aurora and in the re-entry glow of returning spacecraft) typically results not from molecular nitrogen, but rather from free nitrogen atoms combining with oxygen to form nitric oxide (NO).>>
Art Neuendorffer
Re: APOD: Ash and Lightning Above an Icelandic... (2010 Apr
is this what you are referring to? if so, i think it's a star trail too; the ash came in front of it over time. it is parallel with other trails.Ethen wrote:What amazes me is the lateral red hot ejecta above and below the lightning dendrite nearest the ash cloud.
of course he used a tripod. if he didn't, the lightening wouldn't be that sharp & there wasn't any star trail too.Ethen wrote:Camera would have had to been stationary, right?
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wow look at that post! it has been edited THREE times!well i just had to clean up some mess.
Last edited by Amir on Tue Apr 20, 2010 6:03 pm, edited 3 times in total.
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Re: APOD: Ash and Lightning Above an Icelandic... (2010 Apr
I would imagine that its because the dust and other gumph surrounding the volcano is being superheated by the charge from the lightning. So whatever the lightning is hitting on its way to earth is making the light appear purple.
Just a guess, I hope its right.
Just a guess, I hope its right.
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Re: APOD: Ash and Lightning Above an Icelandic... (2010 Apr
Of course, the situation in a gas mixture is more complex. Nevertheless, the purple in the image certainly is coming primarily from ionized nitrogen. This color is very commonly seen in lightning, as well as auroras. As it happens, there are no other atmospheric constituents other than nitrogen that can produce this color under lightning or aurora conditions. It certainly is not a photographic artifact.neufer wrote:Lightning excited air at one atmosphere might (or might not) be a different situation\
(; it certainly isn't as clear cut to me as you make it out).
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Re: APOD: Ash and Lightning Above an Icelandic... (2010 Apr
Chris Peterson wrote:Of course, the situation in a gas mixture is more complex. Nevertheless, the purple in the image certainly is coming primarily from ionized nitrogen. This color is very commonly seen in lightning, as well as auroras. As it happens, there are no other atmospheric constituents other than nitrogen that can produce this color under lightning or aurora conditions. It certainly is not a photographic artifact.neufer wrote:Lightning excited air at one atmosphere might (or might not) be a different situation\
(; it certainly isn't as clear cut to me as you make it out).
I'm with chris........ He gave me money....
JK, makes sense to me! I accidentally posted my post without knowing there was a page 2, it sounded ok so thats why i left it.
Paul
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Re: APOD: Ash and Lightning Above an Icelandic... (2010 Apr
How do you capture such a pic. when it has only mili seconds to perform ? What do you use for camera equipment, timers , sensors ??? How do you get these shots ?
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Re: APOD: Ash and Lightning Above an Icelandic... (2010 Apr
It's not difficult. You don't need anything special, just a camera capable of fairly long exposures. A DSLR or other digital camera with manual mode control works well. You aim the camera wherever you are hoping for lightning, and open the shutter. How long you leave it open depends on the background brightness. The darker the background, the longer you can open the shutter. And then you just keep doing this, over and over. With a little luck, you eventually catch some nice events.rany wrote:How do you capture such a pic. when it has only mili seconds to perform ? What do you use for camera equipment, timers , sensors ??? How do you get these shots ?
It doesn't hurt to have an erupting volcano in your backyard, of course!
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Re: APOD: Ash and Lightning Above an Icelandic... (2010 Apr
Another "scattering" process can be the objective lens used on the camera (some chromatic aberration). This is very common, as lenses tend not to be super corrected everywhere on the spectrum. But the rest is true as well.Chris Peterson wrote:Your reference to different emulsions producing different colors isn't very relevant to a digital image like this. In fact, lightning ionizes nitrogen, which results in the purple color seen here. The main lightning path is saturated, making it appear nearly white. Less bright paths show as a combination of the blue-white thermal continuum and the purple output of ionized nitrogen. The color of lightning can be further modified by scattering processes, depending on the amount of dust, rain, or hail in the air. This lightning appears to be in fairly clear air.neufer wrote:Artifact of photography.
The idea to take lightning pictures of these subjects during the day is to close the photographic aperture quite enough, to make exposures last longer, cause lightning not to saturate too much (not to appear too thick) and to get as much lightnings as we can in the longer exposure.. Some pictures of this volcano also have star trails in them, that illustrates how long the exposure can get!
Fil.
Re: APOD: Ash and Lightning Above an Icelandic... (2010 Apr
is "chromatic aberration" a problem is such a short focal length (Cameras)?Fil wrote:Another "scattering" process can be the objective lens used on the camera (some chromatic aberration).
what Diaphragm is usually used to capture a sharp and not so thick Lightening picture?Fil wrote:...The idea to take lightning pictures of these subjects during the day is to close the photographic aperture quite enough, to make exposures last longer, cause lightning not to saturate too much (not to appear too thick) and to get as much lightnings as we can in the longer exposure...
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Re: APOD: Ash and Lightning Above an Icelandic... (2010 Apr
Chromatic aberration tends to be more pronounced on short focal length (wide angle) lenses, due to the fact that it is difficult to make a lens that can accept light from a wide set of angles without perfectly counteracting refraction problems.Amir wrote:is "chromatic aberration" a problem is such a short focal length (Cameras)?
Do you mean "aperture"? For most lenses you want to try to use an aperture close to the middle of the range. If it is open too much, you can get artifacts from imperfect construction or design of the lens. If it is closed too much, you can get diffraction artifacts. The advice I usually use is "f/8 and be there". Especially for landscape shots where there is not much in the foreground. For this shot, it would probably look identical if shot from f/4 to f/16 (as long as you compensated properly with the shutter speed).Amir wrote:what Diaphragm is usually used to capture a sharp and not so thick Lightening picture?
Re: APOD: Ash and Lightning Above an Icelandic... (2010 Apr
aperture is the diameter of the Lens/Mirror & could not be referred as f/x i guess.WildGuruLarry wrote:Do you mean "aperture"?
the one you mentioned (f/8) is focal ratio (aperture/focal length). which i've heard the term "Diaphragm" (=a device for varying the effective aperture of the in a camera or other optical system) instead of focal ratio when talking about Cameras.
thanks for the hint, i'm gonna try it some day. would f/8 be still appropriate when you're waiting for lightening with open shutter (like this APOD Picture)?
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Re: APOD: Ash and Lightning Above an Icelandic... (2010 Apr
A "diaphragm" is a device for controlling aperture, but nobody really talks about that directly, unless they are discussing how many blades it has. The aperture is the diameter of the opening in the diaphragm. "f/8" would be the focal ratio like you said, but it is also the aperture. For example, on a 50mm lens, if you set a focal ratio of f/8, then the aperture will be equal to f/8, or 50mm/8, or 6.25mm. So most people would say "shoot with an aperture of f/8", rather than "shoot with a diaphragm of f/8". At least, in my experience in North America.Amir wrote:aperture is the diameter of the Lens/Mirror & could not be referred as f/x i guess.
the one you mentioned (f/8) is focal ratio (aperture/focal length). which i've heard the term "Diaphragm" (=a device for varying the effective aperture of the in a camera or other optical system) instead of focal ratio when talking about Cameras.
![Smile :)](./images/smilies/icon_smile.gif)
It really depends on a lot of factors, but that's where I would start (probably with ISO 100 and exposure time of 30s), and then I would adjust accordingly after a few test shots to make sure the background is being exposed properly.Amir wrote:thanks for the hint, i'm gonna try it some day. would f/8 be still appropriate when you're waiting for lightening with open shutter (like this APOD Picture)?
I wish the EXIF data had not been stripped from this photo (and all of his others as well, as far as I can find). It is a very useful instructional tool for us budding photographers.
Re: APOD: Ash and Lightning Above an Icelandic... (2010 Apr
thanks for the explanation. i guess your sentence (At least, in my experience in North America.) reminded me the fact that i'd never speak English like an American. yeah, you're definitely right. i shouldn't have discussed something i've never used or heard in english. in fact in my language we say Diaphragm. that's why i thought everybody should use the same term!!
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