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UltravioletPhotography

I'm hooked - first attempt at UV colour photography of flowers


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Andy Perrin
To put another way - the uv signature is a camera created image rather than something that exists out there. It has no existence without a camera

 

NO! It does have real existence "out there." It is not camera created. The pigments really absorb UV light. Heck, probably the bees can detect it if they get close enough, and certainly other UV-sensitive creatures can see them, like the birds.

 

And by the way if the tree falls in the forest, it does obviously make a sound. The view of reality that claims otherwise is flawed.

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Jim, I've been putting this everywhere.

 

 

Editor's Statement: The floral UV-signature is real. It exists. It is associated with the underlying pigment chemistry in the flower. That a bee does not interpret the UV, blue and green reflective signals from a flower face in the way that was originally postulated does not negate the existence of the pigments and the reflective properties of the flower.

 

All along I've tried to point out the the UV photos we record are only one channel-ed. For any creature having UV visual receptors, the UV photograph represents the possibilities -- but not necessarily the realities -- of their very complex vision.

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Sound is the sensation experienced by a human (maybe other animal) when the pressure waves produced by the falling tree hits the ear.

 

The UV signature is the image produced when a narrow band of reflected "light" is focused and projected onto a 2d plane and transduced into the visible spectrum.

 

We infer from this that a particular arrangements of pigments exist,

 

I think that the UV images seen on this site are beautiful and I really enjoy making and looking at them, but they are photographs. And as such are a construction rather than a direct reflection of reality.

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Andy Perrin
And as such are a construction rather than a direct reflection of reality.

Then there are no direct reflections of reality? This is ridiculous. If everyone's photographs agree that there is something in the middle of the flower that does not show up in visible light photos, then there is something in the middle of the flower. Some people's photos may show it differently than others, but there is definitely something there. The cameras did not all have a convention amongst themselves and agree to show us the same fake flower image.

 

To quote physicist Alan Sokal, whose hoax was intended to show how vacuous this sort of statement is:

Fair enough: anyone who believes that the laws of physics are mere social conventions is invited to try transgressing those conventions from the windows of my apartment. (I live on the twenty-first floor.)
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One can believe that laws of physics are social conventions and also know that jumping out of a window is not a good idea. After all the laws on gravity have changed radically on a few occasions and most physicists would agree that there is a problem reconciling quantum theory and relativity. The laws can be used to make useful predictions, but I think it is a moot point whether these laws and reality are the same thing.

 

"The cameras did not all have a convention among themselves and agree to show us the same fake flower image"

 

Well the cameras didn't, but people did. The camera is modeled on the human visual system and so will show a particular human-centric view.

 

All I am really saying is that it may be informative to take a step back. From the work that Andrea has been referencing it looks like the UV signature does not have any reality for the bee. So trying to see from the bee's perspective might be helpful. Holding on to an idea of reality based only on a human perspective might be holding us back.

 

I have worked as a clinical scientist for many years so I can see the benefits of a scientific approach. I would not want to do away with that. I also find the approach of certain artists infuriatingly irritating, BUT my gut instinct is that science is not the only way to understand the world.

 

The nature of reality debate could run and run as philosophers have grappled with this since at least the time of Plato. A strand of contemporary philosophy called speculative realism takes a stance in favour of an absolute reality against the post-Kantian correlationism (that is that we can only know of the appearance of things, but not things in themselves). From what I have read of that it can lead to some quite bizarre and counter intuitive conclusions.

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What I am reporting is that Horridge does not say what the significance of UV absorbance/reflectance might be for the bee. Horridge says that the significance of UV receptors has not been fully explored.

 

It's entirely possible that those UV-reflecting, UV-absorbing areas mean something more for the plant than for the bee.

 

Direct measurement of reflectivity tells us that there is no doubt about the existence of a UV-signature.

 

I am a scientist/mathematician. Science is the way to understand the world. Philosophy is a way to interpret the world in terms of human experience. I would gently suggest that the two be not confused. Post-Kantian correlationism or other philosophical stances on what is real or not-real are certainly not in my radar. That starts bordering on 'religion' and religion is something best kept to oneself and separated from science, IMHO.

 

Let's just say that it is difficult enough in science to get the facts straight. Periodically we learn new things and revise our old interpretations. That is all that has happened here. Horridge has a newer model of bee vision. It does not negate the existence of UV-signatures. It does not alter what our cameras record.

 

Added: Please see next post. I think I got to barking in this one and came across badly.

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Jim - after re-reading what I just wrote I think I sounded too harsh !!!!! Nothing I wrote was directed at you or at the role of art in interpreting human experiences. I do absolutely love art, like to think about what art means and the benefits of are to us humans and I want to be sure you know that, OK? Please accept my apology if you felt that previous post was "off". I was really just trying to respond and explain a view. That I personally try to keep science & philosophy/religion separate does not mean in any way that others should not make use of both disciplines in explaining the world around us. Sometimes I sound fiercer than I really am. Sometimes I'm an idiot.

 


 

I have a personal policy that as an Editor here on UVP I will never go back and erase anything I wrote in a post because I don't ever want folks thinking I would "rewrite history". If I have to edit something I wrote I will cross it out. Or if I do delete a word I'll say what it was. Or I will mark an addition to a post with an "Added" indication. But everyone kindly note that I do give myself about a half-hour to beat my posts into shape by re-wording, correcting typos and so forth. (Just call me slow in catching typos!) Sometimes I put up an "in progress" note to indicate that I'm still revising.

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That's fine thank you Andrea

 

Can we park the broader issues for now and maybe come at the specific question from a different angle: how would you (or anyone else reading) define exactly what is meant by a "uv signature"

 

I think a lot can be gained from thinking about the relationship between science and philosophy - This book is a great introduction - very short, very readable and very cheap

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Andy Perrin

My personal definition of uv signature for a flower is just any pattern of UV absorption on the flower that is independent of the specifics of how we take the photo (assuming the photo is made using only UV light). I hope this matches other people's definitions!

 

Usually relating to the distribution of reflected intensity, although using the standard white balance we seem able to mostly agree on color too (notwithstanding certain counter-examples like your dark yellow flower that was really gray with a better lens).

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Andy, agreed.

 

Bjørn originally used the terminology "UV-signature" here on UVP with regard to the totality of how a flower looks in reflected UV photography because the terminology "UV-pattern" seemed to imply that there should be stripes or spots or other markings and of course that does not always happen. The UV-signature of a flower may be all UV-dark with no stripes, spots or other marks. Or, similarly, the UV-signature of a flower may be all UV-light. Of course, "all UV-dark" or "all UV-light" must be tempered with the observations that there are usually some relatively brighter or darker bits here and there even in an otherwise uniform UV-signature.

 

I don't think that UV-signature should include the false colours which we bring out by the white balance step during conversion because that is too dependent on the converter, white balance tool, bandwith of the UV-pass filter and other factors. You could make the argument that light and dark tones are also dependent on converter and exposure factors, but I think that is less of a dependence because the relative contrasts can be retained even when adjusting exposures. (And we should try to do that - maintain relative contrasts I mean - in these photos.)

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Ok so "UV-signature" ...[is] ...the totality of how a flower looks in reflected UV photography" seems a reasonable working definition, although I'm sure it could be tightened up.

 

My argument above was that this UV-signature doesn't exist "out there", but is a construction, was based on the fact the this UV-signature is not something that any animal will ever see. As discussed elsewhere many times animals don't see in single waveband channels, what they see depends on how several channels are processed together. It is unlikely that they even see fixed images in the sense of a photographic image, rather the visual information is processed as they move and guides their behavior (paper quoted by DavidO elsewhere).

 

Of course there are chemical and physical properties of the flower that really exist and give rise to these UV-signatures - but the UV-signature itself is how it looks in UV photography and in that sense it is a human construction. To deny this seems wrong on two counts; firstly it is likely to lead to flawed understanding of animal behaviour and secondly I think it underplays the importance of UV photography as part of the overall artistic practice of photography.

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My argument above was that this UV-signature doesn't exist "out there", but is a construction, was based on the fact the this UV-signature is not something that any animal will ever see.

 

I'm not sure the fact that nobody will ever see a UV-signature with their ordinary eyes makes the UV-signature a human construction. Nobody ever sees atoms, but they are not a human construction. Nobody ever sees radio waves, but they aren't a human construction. There are many things we cannot see until we put on special glasses. In the case of UV-signatures, the glasses just happen to be made from BaaderUs. :D

 

And I'm not sure we can say animals cannot see UV-signatures. They can detect it, but just not in the same way the camera can.

 

I'll let others discuss this now. I really prefer shooting UV-signatures to talking about them. :lol: :lol: :lol:

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This seems to have turned into an interesting discussion.

I know most members here are fixated on bee vision. But I have an alternative hypothesis.

I think the flowers have uv regions to act similar to photovoltaic cells. And wonder if the concentration of chloroplasts and other light sensing molecules are in gradients in these regions.

In my limited observations with Dandelions in doors. If you bring one inside, then don't expose to uv or water, it will dry out flower intact. If you hydrate and expose to uv, then it will elongate the stem and change the head orientation. Then when dehydrated will fully go to seed. If you expose to uv, but stay hydrated it will close up the flower and start to push it, but will not drop the yellow cap off until dehydrated.

So I think the uv patern is for the flower to signal seeding internally rather than just for pollination.

But these are age old questions, like why do leaves change color in the fall. That one may be adequatly studied now, but a I am still not sure if a fully agreed upon answer has been found.

 

Also an alternative hypothesis, is Mendel working with camera lens manufacturers from the future designed the pattern to atract future uv photographers to spend all their money on Quartz lenses. However, this hypothesis is less likely.

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Those are excellent observations, David, about the Dandelion.

 

And I'm also enjoying the Time Travel hypothesis having myself spent rather too much money on quartz lenses !!! :D :lol: B) :rolleyes:

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Somewhere recently I mentioned that UV absorption may have benefit to the plant. These papers might be of interest on that.

 

Here is a paper discussing the possible protective effect of UV absorbing pigments. And it also mentions UV-absorption on the underside (abaxial) side of the flower. ((Bjørn Birna and I try to photograph the abaxial sides of flowers.))

https://www.ncbi.nlm...icles/PMC61112/

 

 

 

Here is a paper discussing UV absorption as an enhancement to color saturation in a flower. Only the abstract is available.

https://link.springer.com/article/10.1007%2FBF00937735

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It is so interesting to see these papers. Some efforts we UV photographers have been making since the 1990s are beginning to show up in scientific papers. The reference above from Werner uses an RGB stack made up of R(Vis green) + G(Vis blue) + B(UV red).
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