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UltravioletPhotography

Dandelion


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This was one of my first flower shots at a local park.

I see other places that the UV pics show the center as green, red, and other colors. Some are bee simulated etc. I have not got my head around this yet.

Is the green because that is the color we get by combining gray and yellow? If these other colors I am seeing around for the center of a dandelion are not a combination of something, then how can it be anything but dark if the UV is being absorbed there? Is a life force needed for flowers to show a nectar guide pattern, ie. will a stone dead and dried up flower show a pattern? And if so, what good is that to any bee? I will try this and see. Why can I not pull the green out of the foliage in the UV?

UV is so weird and exciting! So much to learn.

Visible pic: UV pic:

Nikon D70 All same as visible except shutter was 1s (well there was a filter in front)

1/100's

f8

ISO 200

No Flash

 

-Damon

post-51-0-73860500-1402631851.jpg

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Damon,

 

They look fine to me, exactly what I would expect from a dandelion (yes they are weeds here in Australia as well) when taken through a Baader-U filter. I can't get my head around the way others combine UV (as a monochrome) with green and blue channels which are the other colors bees can "see" to get those weird results you mention.

 

Dave

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I have seen dry artificially preserved flowers still retain their UV reflectivity pattern.

 

As far as false colours go - people can do anything and everything in photoshop. Whether its purpose is to emulate animal vision somehow, or a purely artistic endeavor its personal choice. Like this one: http://www.ultraviol...806-hot-target/

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Damon: your UV dandelion is what we would expect using a broad-band UV transmission filter (Baader U 2nd generation) and balancing the image against a UV-neutral target. The darkness of the central part of the flower head indicates there is a good elimination of IR. Same goes for the dark foliage. Some dandelions come over with pure blue scapes in UV and on occasion there is some blue or deep green to the leaves as well.

 

Your dandelion looks a bit like what we in Europe call 'sand dandelions' (Taraxacum sect. Erythrosperma) , these are small, native species on sandy or dry habitats mainly in coastal regions, and recognisable by having reddish fruits. Don't put too much into this as the taxonomy of dandelions is a true mess - suffice it to know that many if not the majority are not weeds at all.

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Damon, the different colours you see in various UV dandelions are all "false colors" produced by the camera or in the editor. Some folks try to simulate bees' visual receptors of uv, blue and green by manipulating the files r, g and b channels. Look up here on UVP Nico's article on how he does this. (I'm on cell so can't go copy the link right now.) In short there are lots of ways to present a UV photo as you have already seen.

 

While it is thought that UV signatures may guide pollinators, all the facts are really not known yet. Why for example do bees/flies visit some flowers which are rather uniformly uv dark? Well, plants have evolved multiple pollination strategies based on: visible appearance, uv appearance, shape, fragrance, texture, nectar, wind, rain water, self-pollination, animals, birds, insects, mimicry and more.

 

There may be some underlying chemistry associated with UV signatures. Maybe absorbing or reflecting UV is somehow important to a particular flowers life cycle in some way.

 

Some flowers do change uv appearance or visual look after pollination. A dandelion loses its rays and becomes a fluff ball. A forget-me-not becomes more uv-bright as it ages.

 

So there are many interesting questions!!! And so we record our uv floral signatures in hopes that maybe they will be useful to eventually answer some of the questions.

 

Your dandelion looks great!

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Damon,

This being one of your first UV shots, I must say it is excellent.

You are obviously already a skilled photographer prior to taking up UV.

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BTW, Damon, I do hope to see some formal botanical posts from you eventually. We want everyone to contribute UV signatures as they can.

 

Added: About foliage in UV - it may appear as grey, blue, green or black in UV after the photo is white-balanced. Depends on the distance to the subject and which plant it is.

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Dave--thanks! We think alike. I am beginning to think it is important to get across the contrast if there is any. I was just wondering if the center of a Dandelion is black(ish) in UV naturally because it is absorbing UV, then how can it be any other color at all? I keep saying color in UV. I guess I should stop doing that. The good thing is we don't always have to understand something to enjoy it (at least I don't!). :lol:

 

Alex H--that's interesting. Thanks for that. Makes me think that in that circumstance the reflectivity had reduced function while it was alive. It could be risky for a flower to invest resources to reflect and have insects visit it also when dead and thus waste it's resources too because there is nothing there for it. The same insect may then not visit a live one if it remembers that. Of course insects may not be thinking at all! Nor may the reflectance have anything to do with insects. Have you seen dead/dried flowers that retain nectar guide patterns (dark)?

 

Col-thanks!

 

Bjorn-Thanks, so I am on course then which is good to know. I took this in the sandy pine barrens so you landed pretty close with that ID. And I live in the coastal plain so bang again. You sound like you have taken your share of Dandelions and have had fun trying to ID them.

 

Zach-Thanks!

 

Andrea-Wonderful information for a beginner like me and to the point so I thank you for that. If they are false colors then what would I see if I removed the colors? A black and white photo? Those are colors too though as I can see them. See how quickly I can paint myself into a corner!

The UV dark flowers that get visited by insects sounds like the attraction is not in the pattern.That sure is a lot of pollination strategies. The asters appear the most successful and I would love to take a UV of a 40 million year old aster to look for patterns. I wonder if any UV signatures remain in a fossil? Since the dandelion appears dark, does it follow that it is also warmer there from the sun? Like wearing a black shirt in summer. Could the center be giving off heat as well, which may allure a bug? You are right--there are lots of cool questions. It's like I landed on another planet. My last question for you Andrea, if a bee is seeing visible and UV then does it likely see a combination of both? I will get some formal post going as soon as I can get some more pictures. I have some of Gazanias but not much else that you already don't have.

 

JC-thanks for the compliment. I see that you also have very keen skills. I just looked through your link below your name and holy moly, that is tremendous and something to be proud of. Awesome body of work there! So you are the one I should ask this question to: Why does sunscreen absorb UV and not reflect it? Absorbing something normally means it becomes part of you

 

-D

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Alex H--that's interesting. Thanks for that. Makes me think that in that circumstance the reflectivity had reduced function while it was alive. It could be risky for a flower to invest resources to reflect and have insects visit it also when dead and thus waste it's resources too because there is nothing there for it. The same insect may then not visit a live one if it remembers that. Of course insects may not be thinking at all! Nor may the reflectance have anything to do with insects. Have you seen dead/dried flowers that retain nectar guide patterns (dark)?

 

I do not understand how are you making these conclusions from what I said: I have seen dry artificially preserved flowers still retain their UV reflectivity pattern.

 

First of all, UV reflectivity pattern will include both hightly reflective and non-reflective areas.

 

Second, I was speaking about artificially preserved flowers, cut and dried for herbarium. Not the flowers that completed their life cycle in nature. Such flowers, if pollinated, will turn into fruit. If insects visit the fruit, they will do it for completely differen reason.

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Since the dandelion appears dark, does it follow that it is also warmer there from the sun?

Areas which are black to human vision absorbs all human visible wavelengths.

UV-dark is not black. UV-dark areas absorb UV wavelengths.

An area can be black to human vision but also reflect UV.

I do not know whether a UV-dark area is necessarily warm.

 

if a bee is seeing visible and UV then does it likely see a combination of both?

A bee has UV, blue and green visual receptors. If any two receptors are stimulated, then the bee sees a color which is a combination of those two receptors. Thus bees have 6 basic colours which are typically named in the scientific literature as: blue, cyan (blue-green), green, UV-blue, UV-green and UV. If all three of the bee's visual receptors are equally stimulated, then the bee sees "bee white". If none of the bee's visual receptors are stimulated then the bee sees "bee black".

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Alex H, I may have stated some things in a confusing manner. That's probably because I don't know what I am talking about. I eventually will be smarter with this UV. My suggestions and questions will be soon over when I have mastered this UV stuff--say in around 40 years. I was not making any conclusions though there, only expressing ideas.

I think I see where I got turned around. I thought the UV areas of a flower (bulls-eye, nectar guide) were dark areas thus would not be considered a UV reflected pattern but an UV absorbed pattern. How can a UV reflectivity pattern include something that doesn't reflect in UV? That's confusing.

 

I was not suggesting an insect may visit an artificially preserved flower but was wondering if they would visit a dead one that may or may not still retain it's pattern. Just trying to decipher if some of the Nectar patterns/guides are associated with being alive. I had a lot of my Rhododendron flowers come off and fall to the ground during a heavy rain storm not long ago and after a couple/three days, I saw some of those flowers were still open but somewhat dry, wrinkled & dead looking. While the bees were visiting the ones still attached to the shrub, I did not see a single one go on any of the ones that fell off. I will try and find this out too by some testing later. Although it will have to be something else as all the Rodo's are done blooming.

 

Andrea-Dark Dandelion, thanks and that makes perfect sense

Re:Bee colors--makes sense as well. Thanks you for you time and all your answers.

 

Re: UV warm areas:

Exciting but preliminary update! I looked at my Gazania UV photos I took recently and checked out the very pronounced dark UV absorbed areas that encircled it. So I took a digital thermometer gun and shot the laser (while flower was in the sun) at the tips of the petals and went down towards the center from there. When the laser hit the area that corresponds to the UV dark areas I noticed before--the temperature went up! I did this multiple times and had a second person watch and they agreed. I did a video as well but need to do it a tad more professionally. I also need to have a steady light source as I am not sure the sun was shining exactly the same during the whole procedure, but it looked like it was. So my initial thoughts are that the UV dark areas are indeed warmer, at least in the Gazania I tested. There could be many things that a warmer flower part or center could influence. I will try this whole thing again tomorrow and see if I can repeat it.

 

-D

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I think I see where I got turned around. I thought the UV areas of a flower (bulls-eye, nectar guide) were dark areas thus would not be considered a UV reflected pattern but an UV absorbed pattern. How can a UV reflectivity pattern include something that doesn't reflect in UV? That's confusing.

 

Because the therms reflection, transmission and absorbtion are part of the same equation. In simple theory, 100% absorption will be equal 0% reflection and 0% transmission. An how would you describe the surface that absorbs 50% of electromagnetic radiation (light) and reflects 50% of electromagnetic radiation radiation? Being 50% reflective or 50% absorbtive?

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I usually call that "moderately UV-absorbing" or "moderately UV-reflecting" accordingly as the area falls slightly to the UV-dark or slightly to the UV-light side of false colour midtone grey. :) But the point is well-made about the terminology.

 

So, let's remember that Bjørn has proposed calling the overall look of a flower its UV-signature rather than using such terms as "UV-reflectivity pattern" or "UV patterning". The term UV-signature covers those cases where there is an almost uniform UV-absorption/reflection over the entire flower (i.e., little obvious 'patterning') as well as those flowers which do have obvious bullseyes or other UV-dark markings in UV.

 

UV-signature

UV-signature

UV-signature

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Why does sunscreen absorb UV and not reflect it? Absorbing something normally means it becomes part of you

 

Well, since you ask, when a molecule (active ingredient) in the sunscreen product absorbs UV radiation then some molecule that is part of you (such as DNA) does not and is protected. This is referred to as a chemical sunscreen agent, with energy dissipated primarily via vibrational relaxation (heat) or through radiative (fluorescence) or some type of non radiative energy transfer (sensitization). The physical sunscreen agents, such as TiO2 and ZnO, also absorb UV, with much lower extinction coefficients, but act primarily via scattering radiation, a component of which is indeed reflected out of the layer of product on the skin.

- JD

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Alex H--What Andrea said. :)

Andrea-thanks again

 

JC--I had a feeling I would get a cool scientific answer from you. Thanks and that is the detail I was hoping for. Interesting.

 

-D

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