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

[JMC]

It's time for a confession. I originally come on here as part of my UV research into sunscreens. I must admit I was amazed at the UV photos of flowers I saw, but that wasn't what I was after, so I didn't bother trying to capture any. However it's a sunny day, and I've just been out in the garden to take some images of the flowers I have there - a Buttercup and some Daisies (sorry, I don't know the Latin names, and this isn't meant to be a formal post), and wanted to share them;

 

 

 

These were taken with a Canon EOS 7D mkI, converted to UV by ACS, and a Nikon 105mm UV Nikkor (f11, ISO400 and 2.5s exposure). Images captured in RAW format and white balance set in Darktable (2768K and tint 1.757, based on a photo of a sintered PTFE disk under the same lighting). Other than that they haven't been processed further.

 

I have to admit, I kind of love it now, and I can see why so many of you enjoy taking these UV photos of plants. Need to wait for a Dandelion now - been pulling them out whenever I see them, as my wife hates weeds (even when I call them wildflowers).

 

One thing that did surprise me, it's rare in the UK to get a completely still day. It's a waiting game to get a few seconds of 'breeze free' time to capture an image.

[Jim Lloyd]

Snap !

 

Unfortunately I do not know if there is a cure !

 

Maybe when winter comes I’ll get back to dreary landscapes - but for now let’s go with it !

[Andrea B.]

Another amateur botanist in the making !!! :D :D :D

 

We encourage anyone who is into UV photography of any type to also consider contributing to our botanical section occasionally. Bjørn Birna and I will help with identifications of wildflowers. And I always am available to help with or review the formatting of the entry.

 

So Jonathan, please consider contributing your buttercup and the other flower, OK?

 

For help with a flower ID, make a snapshot of the leaf, the stem, the (top) face of the flower and the sepals or involucre under the flower. Also make a photo of the entire plant so that its habit and habitat can be seen. (Small versions of ID photos can be added to a botanical posting to illustrate the ID.) Note characteristics of the plant. Is it hairy or not? Does it droop or trail? How many anthers and styles does it have? And so forth.

 

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The natural world holds such delights.

 

And also leads to the collection of way too many field guides in my particular case. I now have multiple field guides for stars, insects, butterflies, caterpillars, moths, birds, reptiles, trees, weeds, mushrooms, moss, lichens, mammals, fish and so on.

 

Fortunately these days identification guides are beginning to appear online. We have some excellent botanical resources for North America, for example. Still, there is something appealing about paging through a lovely field guide and lingering over illustrations of things one has not yet seen.

[Andy Perrin]

I have found it particularly hard to shoot buttercups, though. Not only do they have those extra thin stalks, that waxy layer causes all kinds of issues in focusing for me.

[Andrea B.]

Buttercups do indeed have specular reflection problems. Cross-polarization anyone? :D (Reference to Jonathan's posted paper.)

 

Somewhere I posted a note about how Buttercups can be rain pollinated because of that waxy area in the cup of the flower. I'll try to find the link later.

[Andy Perrin]

Also the wind issue is a problem everywhere I think? Certainly here in Massachusetts I have just as much trouble finding a two second interval entirely free of wind.

[Andrea B.]

Patience grasshopper !!

Bwah-hah-hah-ha-ha........

[Cadmium]

Jonathan, Great shots!

[Cadmium]

Maybe I missed the filter you used...?

I would like to see that first shot, shot with UV+Blue+Green stack.

[JMC]

Maybe I missed the filter you used...?

I would like to see that first shot, shot with UV+Blue+Green stack.

This was with a UV conversion from ACS. So the filter is their one, which they do not share the spectra for.

[JMC]

Andrea, I will put these up more formally, however while the weather was good I did go into the garden again. This time with the Zeiss UV Sonnar on a 35mm extension tube with the ACS modified Eos 7D mkI UV. Back to the Buttercups again. This is a full (uncropped) and a crop from the same image. Images have been reduced in size for the forum.

 

 

 

To be honest I think the UV Nikkor is sharper, but this was just to see what it would do.

 

It's interesting and I saw this with the UV Nikkor too - the edge of the petals is highly UV absorbing. I wonder why that is?

[Andy Perrin]

Yep, my buttercups have the dark edges also:

[Andrea B.]

Buttercup UV-black edges....who knows why?? Just one of the many interesting things seen in nature. And we are lucky that we get to explore those features "hidden" from most people. :D

 

You can try to think these things through from a bee vision color model. But we all need to learn the limitations of our attempts at modeling bee color vision. See some references which follow my flower illustration that explain how bee vision really works.

• The center and edges of these two buttercups absorb UV and reflect yellow. So any animal which has the "right" visual receptors will have a vis receptor stimulated by that yellow reflection. The bee probably has its green receptor stimulated and interprets a green or yellow-green signal. (I do not know if it has been nailed down by bee vision researchers that bees physically detect yellow reflection.)
  

• In contrast, the false yellow portion of the buttercups reflects both yellow and UV. So the bee's UV receptor and green receptor might perhaps be simultaneously stimulated* to produce a colour, imaginary to us humans, which we might label +UV+G or UVGreen. Thus the bee is seeing possibly something like the following.
  

From what I have read that Ranunculus edge is very important to the bee. Its color, per se, is not important although changes in the intensity of the colour might be important. It is the edgeness of the edge that acts as a bee visual cue.

 

 

*I think this is probably an erroneous assumption by us bee color vision enthusiasts that both Green and UV receptors are stimulated to produce a bee color.

 

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(....here Andrea must temporarily enter her didactic "teacher mode. Please simply ignore if not interested.....)

 

ADDED: After writing this below, I reread How Bees Distinguish Colors and decided to post about it here: http://www.ultraviol...we-cant-really/ It is more succinct than what I wrote below.

 

The eminent bee vision researcher Adrian Horridge (who is all I read these days!) tells us in his paper How bees distinguish colors.pdf that bees "cared nothing for colors, layout of patterns, or direction of contrast". He also tells us in Parallel inputs in bee vision of colour.pdf that "UV inhibits the blue channel in bees [10] and UV has never been seriously implicated in bee colour vision."

 

What bees do care about are certain visual Cues that when combined enable bees to store a Landmark where nectar and pollen rewards are available.

• Areas (unrelated to Edges)
  
• Edges (unrelated to Areas)
  
• Position of Center
  
• Black Spot
  
• Color == as a visual stimulus, but not as a color. (Does that make sense? It is non-intuitive.)
  
• Radial Edges
  
• Bilateral Symmetry
  
• Average Orientation
  
• Circular or Tangential Edges (I don't know what this means.)
  
• Heterchromatic Modulation
  
• Intensity Modulation
  
• Green-sensitive Edge Modulation (recognize this possibility in the edges of the Ranunculus when re-interpreted in bee colours?)
  

So bees are not looking for the UV-signatures our UV-cameras can capture. Bees are not looking for the geometric shape of a flower although they do recognize cues for bilateral symmetry and radial edges. UV appears not to be used by bees as a colour, per se. Bees respond to passing edges.

 

We cannot apply human vision principles to bee vision.

 

However we should continue photographing flowers in UV and also perhaps with our UV+B+G filters because it enables us to find the edges and contrasts and other cues which might appeal to the bee.

(....got a bit anthropomorphic there with that 'appeal')

[Jim Lloyd]

Interesting - very interesting ...

 

And Bjørn pointed out the importance of the bright edge in the birds foot trefoil which has a uv dark flower - kind of inverse to the buttercup ?

 

See http://www.ultravioletphotography.com/content/index.php/topic/2746-birds-foot-trefoil-an-interestingly-boring-yellow-flower/page__fromsearch__1

[Andrea B.]

Let's think about that Trefoil edge.

 

I'll use my (very incomplete) knowledge of how bees really see.

 

The flower reflects yellow everywhere and reflects UV only on the edges. Bees measure blue content and look for green edge contrast. UV is used by the bee only to know where the sky is. So, what do we have?

 

Relative to the typical green background the visible yellow flower has significantly less (maybe no) blue content. Thus the flower can be detected in a large angular visual field by the bee's blue content measurement process.

 

The yellow reflecting edge has green content and as the bee files that could signal a green contrast change and thus orient the bee as to how to land on the flower. So it is very important, it seems.

 

I'm new to this way of analyzing how the bee sees. And probably oversimplifying. Or getting something not quite right.

[Jim Lloyd]

Is it known how sensitive to uv bees are ?

 

I have been thinking as I take uv pictures , that the amount of uv around is pretty low and variable. Especially in a wood - where lesser celandine grow on shady banks. The number of “yellow photons” will far outweigh the uv ones, so unless bees are more sensitive to uv it seems rather unlikely that the uv signal is critical ???

[Andrea B.]

Jonathan, I've heard that about the UV-Sonnar. But I think you would have no trouble selling it if you don't like it.

 

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Jim, I haven't read anything about how much sensitivity a bee has to UV. In terms of receptors per bee eye facet the count is 1/6/1 for UV/Green/Blue. But Blue content in an area is a preferred Cue in large angle bee vision for detecting flowers. Followed by modulation of edge contrasts detected in small angle vision (hence more Green receptors) as a Cue by Green detectors .

 

Nevertheless, the UV receptor is critically important for the bee. For one thing, the bee has to know which way is up in order to fly properly so its UV receptor tells it where the sky is. UV detection is also used in escape, but I didn't find an example of what was meant by that. Escape from predators? Escape from the hive as in 'going out to forage'?

 

UV is not used by the bee in foraging. The Horridge papers simply say that not much is yet known about the bee's UV receptor. Horridge says UV detection might possible combine with other detection in a useful way to the bee, but we don't know what such a combination might be. Yet.

 

Then Prof. Horridge goes on to say that bees are easy to train, bee experiments are easy to set up and inexpensive and we should all borrow a hive and try it out !!!!! :D

 

Not everything is pollinated by bees.

Hummingbirds, moths at night, wind, rain, beetles & bugs, self-pollination, the hand of man, spiders, lizards, and more.

 

I spent this entire day reading about bee vision. I am bee vision-ed out.

[Andy Perrin]

Andrea, regarding the way the bees see, doesn't that cast doubt on the hypothesis that they use the dark UV bullseye for pollination?

[Andrea B.]

You have to look at the all the reflectivities of the flower. Our UV photos only show one channel.

What does a UV-dark bulls-eye which we capture in a UV photo actually signal to the bee?

 

I haven't yet entirely figured it all out yet. I'm working on it! I could make some sense out of the Yellow Bird's Foot Trefoil posted recently in another thread. But I have to think more about the above Ranunculus in terms of Horridge's model of bee vision. I'll give it a try.

 

Yellow reflectivity means blue is absorbed. So the Bee sees the buttercup and measures no blue content. Hence the buttercup is detected as "bee black". (An absence of a blue content Cue is also a Cue.) So this bee black means something to the bee when lack of blue is measured relative to the buttercup background blue content. The bee can find this yellow Ranunculus.

 

But what about that UV absorbing center? Darned if I know.

[Andy Perrin]

Andrea, you said in the other thread that they only use the UV for finding the sky. You quoted that researcher as saying the UV is more a of a signal for which way is up?

 

From the other thread:

UV: The UV receptor is used by a bee to detect the direction of the sky for level flying or for escape. UV plays no role in bee foraging. UV is not really a colour to the bee as we humans think of color.

 

If it plays no role in foraging, then why the long-time claim that the bullseye is for attracting bees?

[Andrea B.]

If it plays no role in foraging, then why the long-time claim that the bullseye is for attracting bees?

Everybody was wrong.

 

I'm not meaning to be sarcastic with that answer. As often happens in science, new facts and observations change interpretations and provide new explanations.

 

Besides which, as I've written many times, the UV photograph is only one possible "channel" of animal or insect vision. No animal/insect sees only in UV. You have to consider the all the reflectivities of the flower together with the specific types of receptors the animal/insect has. I've tried to show that occasionally in my little charts. But I think those are mostly ignored because mostly here we discuss gear and show photos. Which is good -- that *is* the purpose of a photo forum after all. But now, as it has turned out, my little charts are misleading as well even though they do not typically feature a dark center when interpreting bee vision.

 

I wish I had read the Horridge papers in depth when I first learned about them. (From Dr. Zach, perhaps? Can't remember now.)

 

But this newest model of Bee Vision does not explain why UV-signatures exist in flowers. So who knows how that will eventually shake out. Just a by-product of underlying pigments or chemistry? Meaningful to an insect in some way not yet discovered? I'd like to still be around when more is learned about UV-signatures.

[nfoto]

We discover, by our photography, that these signatures *are* there. That is in fact all that matters.

 

Whether Nature has a Meaning to its manifestation is a question way beyond Photography anyway. We are only the conveyors of information gleaned and that has inherent value on its own.

[Jim Lloyd]

I mostly agree, but if I was to play devil’s advocate I would ask in what sense do these signatures exist out there in an objective sense ? Do they actually only exist in our photographs as revealed by human made instruments. Are they “there” in that sense for bees other animals ?

[nfoto]

We know these signatures arise because there are interactions between the floral structure and UV. To me, that suffices. The phenomenon is for real. Its importance is open for speculation.

[Jim Lloyd]

Like the tree that falls in the forest, making no sound unless there is someone to hear it, so the uv signature is only real if there is a camera to capture it and human mind to contemplate it. It has meaning, but that meaning is embedded in human culture. To try to find it’s meaninf for the bee is futile, as it doesn’t exist for the bee anyway

 

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

 

Just a position to provoke debate and learning ...