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Helianthus annuus [Common Sunflower]

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#1 Chelidon

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Posted 31 July 2020 - 14:33

Giglio, F. (2020) Helianthus annuus L. (Asteraceae) Common Sunflower. Flowers photographed in ultraviolet and visible light. UV-induced visible fluorescence also shown. https://www.ultravio...nuus-sunflower/

Specimen
Sunflower at the early stage of blossoming collected from a cultivated crop. Flower stem was kept for some days in a water jug to follow the complete blossoming, all the photographs were taken in a dark room.
Location
Fiorenzuola, Italy
Date
19-24 July 2020

Operations
The UV reflectance photos were shot using long exposure and doing light painting with a Convoy S2+ (Nichia 365 nm), using a modified camera. The second of the two photo was shot after 5 days.
The visible photo was shot with standard tungsten light (dark-body spectrum centered on orange), using a standard camera.
The UV flourescence photo was shot using long exposure and doing light painting with a Convoy S2+ (Nichia 365 nm), using a standard camera.

1) VIS, ISO 100, f/8.0, 4 s
Attached Image: Heliantus_VIS.jpg
2) UVIF, ISO 100, f/8.0, 15 s
Attached Image: Heliantus_UVF.jpg
3) UVa, ISO 80, f/4.0, 4 s
Attached Image: Heliantus_early-blossom.jpg
4) UVa, ISO 80, f/5.6, 8 s
Attached Image: Heliantus_full-blossom.jpg

Comments
I know it is a popular subject to start with, but I have found interesting to notice how much change the center disk because of the opening of the disk florets during blossoming. In image 3 only the disk florets on the external circumference are starting to release the pollen, while image 4, after 5 days, shows the disk completely covered with pollen. The UV reflectance of the disk changes mainly because of the pollen fluorescence which brightens up the contrast with the well-known bull's-eye pattern in the corolla. Conversely, the ligulae on the corolla do not show any evident modification. The pollen fluorescence is shown clearly in image 2. I have not taken the same UVIF after 5 days, but it was obviously very brightly fluorescent when illuminated. In image 3 there are even some droplets on the disk that could be seen also on image 1 for reference. I suppose it was nectar and not mist.

Reference
1. Wikipedia (2020) Helianthus annuus. Wikimedia Foundation, San Francisco, CA.

Hope you enjoyed.

#2 Chelidon

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Posted 31 July 2020 - 14:40

Pardon, lingulae instead of ligulae it is obviously a lapsus linguae (it is a fine verbal joke), due to the closer meaning of tongue in my latin rooted mother language. :lol:

#3 Andy Perrin

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Posted 31 July 2020 - 15:23

Heee. Nice photos! Is there a benefit to going below ISO100?

Also, what cameras and lens and filters did you use for the shots? I think that belongs on the formal entries?

Edited by Andy Perrin, 31 July 2020 - 15:31.


#4 Stefano

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Posted 31 July 2020 - 16:26

My sunflowers still have to bloom. Maybe I planted the seeds too late (I think in May). I hope they will bloom this year.

#5 Andrea B.

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Posted 31 July 2020 - 17:34

Fabio, grazie for this excellent contribution to the botanical section.

(I will later make minor edits so that the post is index-able and search-able.)
Andrea G. Blum
Often found hanging out with flowers & bees.

#6 Chelidon

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Posted 02 August 2020 - 09:03

Thanks, I would have liked to edit for the typo errors but I have found the locked edit button.

View PostAndy Perrin, on 31 July 2020 - 15:23, said:

Heee. Nice photos! Is there a benefit to going below ISO100?

Also, what cameras and lens and filters did you use for the shots? I think that belongs on the formal entries?
Ah well... no benefit at all! :lol: They are simply two different cameras (the first two images are taken with a standard not modified, the others two simply cannot) with different base ISO. I will explain later in another thread about this equipment, because I prefer to discuss widely about the pros/cons of this solution that is pretty cheap. Obviously UV reflectance was made with a two filter stack, otherwise I would have collected a lot of fluorescence signal.

At the moment I will just let you the spectra for that stack I measured with a spectrometer.
Attached Image: uv-pass+vis-block.JPG
I think it helps to frame the two UV reflectance images (3, 4).
Attached Image: unknown-IMX.JPG
For the two visible images (1, 2) the spectral sensitivity should be (not exactly is, probably: pentax, sony never disclose anything about it) similar to this one more or less (taken from this reference).

#7 JMC

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Posted 02 August 2020 - 10:42

Depending on which camera you have, I've measured the spectral response of the Sony A7III here (modified for multispectral and standard);

https://jmcscientifi...-the-beginning/

https://jmcscientifi...era-conversion/
Jonathan M. Crowther

http://jmcscientificconsulting.com

#8 Andy Perrin

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Posted 02 August 2020 - 16:20

Interesting. Please do make that equipment thread, it’s not good to be too mysterious about these things since the point of having this board is to share technical details as well as photos. And we cannot properly interpret a photo without those details, or help with any problems.

Re your stack - that will certainly leak infrared in sunlight. In general if any IR bump is visible on a linear scale spectrum then it will contaminate an image in sun.

#9 Stefano

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Posted 02 August 2020 - 18:50

View PostAndy Perrin, on 02 August 2020 - 16:20, said:

Re your stack - that will certainly leak infrared in sunlight. In general if any IR bump is visible on a linear scale spectrum then it will contaminate an image in sun.
Maybe it is a second-order diffraction spectrum (if his spectrometer uses a diffraction grating). Otherwise, if that is infrared, it will certainly leak quite a lot.

#10 nfoto

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Posted 03 August 2020 - 21:56

The Asteraceae species like Helianthus have ligulate florets (peripheral rays) and disc florets (centre).

#11 Andrea B.

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Posted 05 August 2020 - 18:06

Editor's Note: Minor changes made for indexing and terminology. Typo fixed.
Chelidon, please let me know of any problems with changes.
Andrea G. Blum
Often found hanging out with flowers & bees.