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Flower with nectar guides

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#1 Stefano

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Posted 26 January 2020 - 22:06

Hi, back in September (when leaves and flowers were still abundant), I took some UV, VIS and IR photos of this flower (and other flowers). It is the "visible yellow, UV false yellow" flower type (like Rudbeckia hirta, dandelions, sunflowers, etc.). I never obtain strong colors in UV, and the colors are stronger in videos than in photos, for some strange reason.
Also the IR shots are not very good, but I will post them anyway.
I would like to know what flowers it is, so I can buy it since it has some really nice nectar guides.

Also, it isn't really noticeable in the visible photos, but I could tell with my naked eyes that this flower had nectar guides. Usually, if you see yellow flowers that are slightly orange in the center it means that they have a dark center in UV. This was a great example. To my eyes this flower was yellow with a light orange ring, right where the black pattern starts. It was a ring, not a filled circle, though.

Cameras and filters:
Samsung Galaxy A5 2016 rear camera (SM-A510F), unmodified, for visible and IR.
Full spectrum Panasonic DMC-F3 with ZWB2 (2 mm) + chinese BG39 (2 mm) for UV. I call it "chinese BG39", how should I call it?
Black pen ink filter for IR.

"big area" shots:

UV, f-stop: f/2.8, ISO 1600, 1/15 s exposure
Attached Image: P1000770.JPG

VIS, f-stop: f/1.9, ISO 40, 1/1241 s exposure. Overexposed, I know.
Attached Image: 20190909_110401.jpg

IR, f-stop: f/1.9, ISO 200, 1/8 s exposure
Attached Image: 20190909_110353.jpg

close-ups:

UV, f-stop: f/2.8, ISO 1600, 1/25 s exposure
Attached Image: P1000774.JPG

VIS, f-stop: f/1.9, ISO 40, 1/4310 s exposure.
Attached Image: 20190909_110630.jpg

IR, f-stop: f/1.9, ISO 80, 1/10 s exposure. I tried 8 times, but the phone couldn't focus.
Attached Image: 20190909_110719.jpg

#2 Andrea B.

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Posted 27 January 2020 - 16:48

Stefano, I am not sure what this flower is. I'm going to look further. It might be a Heliopsis.

Here is a link to one Heliopsis which shows a broad UV-absorbing bullseye.: https://www.ultravio...n-smooth-oxeye/

Of course, within a genus we can and do find differences in the UV-signature amongst individual species. But there tend to be more similarities than differences within a genus.

It is always more difficult to identify a garden plant because there are so many hybrids and cultivars. :wacko:

Look for some sunflowers to buy at the larger grocery stores or at a flower seller. They have a large central UV-dark bullseye. Some sunflower species also have some interesting UV-dark (very) narrow stripes.




I never obtain strong colors in UV
I do not know how you are converting/processing your photos. But you could attain a higher false-colour saturation (where possible) by setting a higher saturation either in the camera settings or when you convert the raw file. Of course, there are some false-yellow flowers which simply do not have a high yellow saturation. And some which offer quite a lot of false-yellow. Look through the Helianthus photos in the botanical section to see examples. Here are two links.

This sunflower photographed by Andy Perrin shows a low saturation false yellow:
https://www.ultravio...850nm-ir-uvivf/

Three sunflowers showing 3 different false-yellow saturations:
https://www.ultravio...-straightedgeu/




I think the Galaxy A5 has trouble focusing because the lens is causing so much flare in IR. Also it appears that it cannot close-focus in IR. Those long IR wavelengths! But the photos are still useful to show the reflectivity of this flower in IR.




Look for a potted Gazania flower to photograph in UV and IR. Here in the US we can find these at grocery stores and at plant nurseries where gardening plants are sold. Gazanias need lots of sun but no cold. Most Gazanias have a small amount of IR-absorbing patterning which is quite fascinating to see given that most flowers are entirely IR-reflective.
http://www.ultraviol...rigens-gazania/
https://www.ultravio...__fromsearch__1
Andrea G. Blum
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#3 Stefano

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Posted 27 January 2020 - 20:28

View PostAndrea B., on 27 January 2020 - 16:48, said:

I never obtain strong colors in UV
I do not know how you are converting/processing your photos. But you could attain a higher false-colour saturation (where possible) by setting a higher saturation either in the camera settings or when you convert the raw file. Of course, there are some false-yellow flowers which simply do not have a high yellow saturation. And some which offer quite a lot of false-yellow. Look through the Helianthus photos in the botanical section to see examples. Here are two links.
What I do is put the filter on my camera (which, I remember you, is a "compact" type camera, the type with fixed lenses), I WB on a paper tissue (I don't have a PTFE target, and cellulose appears to have a very flat reflectance curve, but I never checked this aspect), and then I take photos or videos. As simple as that. No post-processing, no custom WB after I take my photos.

In that occasion I also made two videos, and you can see the difference.
Here is a frame from one of those videos. Probably the exposure was 1/30 s, and everything was basically the same.
Attached Image: 1 - Copia.jpg

And, if I use the "multishot" mode (you keep the button pressed and it keeps taking photos), the first one has worse colors than the others.

#4 Andrea B.

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Posted 27 January 2020 - 21:14

You could try setting the Color Mode in the F3 to Vivid. That should give more false color.

I should have added: That should give more false color if it exists. Some subjects have no false colour in UV.
Andrea G. Blum
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#5 Andrea B.

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Posted 27 January 2020 - 21:21

I should have added this: White paper often has added optical brighteners which could possibly skew the white balance setting.
Andrea G. Blum
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#6 Stefano

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Posted 27 January 2020 - 22:01

View PostAndrea B., on 27 January 2020 - 21:21, said:

I should have added this: White paper often has added optical brighteners which could possibly skew the white balance setting.
Yes, that's why I don't use normal "printer" paper. It isn't coloured in UV, it appears grey, since it converts some UV into blue light.

This is an example of what I usually do.

f-stop: f/2.8, ISO 800, 1/20 s exposure, sunlight.
Attached Image: P1010088.JPG

Normal paper (with pencil writings and drawings) and "tissue paper".
f-stop: f/2.8, ISO 200, 1/50 s exposure, 365 nm LED.
Attached Image: P1000957.JPG

#7 nfoto

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Posted 28 January 2020 - 08:21

My impression is this might be a Calendula species. However, in the vast Asteraceae impressions are not very reliable when it comes to exact species identification; only using a good flora and examining the actual plant will do.

Paper is not an adequate starting point for setting "UV white" balance. If you cannot get hold of pure PTFE, the expanded foam of packing material (blackish in appearance) tends to be quite useful as it photographs UV-grey.

#8 Andrea B.

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Posted 28 January 2020 - 09:05

Unbleached tissue paper might work well enough, Birna. I think I know where to get some to try. If I do find it, then I’ll compare it to Spectralon and PTFE.

Good call on the possibility of Calendula. It could be that flower.
Andrea G. Blum
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#9 nfoto

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Posted 28 January 2020 - 09:30

My gripe with paper is that the material is too variable in spectral terms. Optical brighteners or other substances may have been added and there is no way to ascertain this by eye only. If the paper fluoresces brightly under UV light one can be sure something has been added.

Expanded foam is, on the other hand, pretty reliable. You find the material easily, for example, used as inserts or padding. In the test picture below, expanded foam is the background (insert in a Pelicase). My notes were written on coarse paper and in this scenario, it is quite neutral. However, there is no guarantee this will occur in UV.

Attached Image: T1503226480_UV_Nikkor_Tussilago_BaaderU_sRGB.jpg

Full-spectrum Nikon D600, UV-Nikkor 105 mm f/4.5, Baader U (2nd gen.), Broncolor studio flash with uncoated xenon tube.

Note that changing the colour space into sRGB has thrown off the original w/b.

#10 Stefano

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Posted 28 January 2020 - 13:39

Normal white paper has a very strong blue fluorescence, which is "activated" by violet and ultraviolet light. This makes it less reflective than PTFE or other materials in UV, since a portion of UV light isn't reflected back as UV. You can see this in my image above. The paper of the tissue, instead, has a pale white fluorescence, and is very reflective in UV. Cellulose, as everything, will eventually absorb as you go deeper into UV, but it seems to me that, at least in the upper half of UVA, it is nearly 100% reflective and, most importantly, has a flat reflectance curve. Further tests must be done in order to be sure of this.

Edited by Stefano, 28 January 2020 - 15:23.


#11 Andrea B.

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Posted 28 January 2020 - 17:15

Stefano, here is something off topic: http://uvirimaging.com/
That is the UV/IR website of David Prutchi. If you are not already familiar with it, then I think you might like to take a look. David is quite inventive and also has a lot of do-it-yourself projects available on the website.
Andrea G. Blum
Often found hanging out with flowers & bees.