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UltravioletPhotography

First flower attempt - gorse


Jim Lloyd

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I have always done landscape photography up until now and I don't even posses a macro lens as I have never done any close work. It was blowing a gale outside so I decided to try something indoors. Only light source was daylight through a window, so I know that cuts UV (I am not sure exactly where, I think a reasonable amount of UVA is passed?).

 

Only flowers around at the moment is gorse (a few snowdrops are struggling out) (added some dead twigs with lichen also)

Nikon D3200 converted

UG1 2mm + BG40 2mm

Nikon E 50 mm

f 5.6

ASA 200

20 seconds exposure

WB on teflon tape (out of shot)

Saturation increase and some other processing in Lightroom

Image is cropped

 

I know I have a long way to go - but pretty pleased with that ...

 

post-175-0-01945200-1517069965.jpg post-175-0-85606400-1517069977.jpg

 

post-175-0-93445300-1517069990.jpg post-175-0-37167000-1517069999.jpg

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Gorse Ulex europaeus has a distinct UV signature that comes well across in your photo. Kudos with that attempt.

 

Interesting "UV flower shots" needn't be done with a close-focusing lens. I've done them with anything from fisheyes to extreme focal lengths. Here is a wide-angle lens used to capture Andrea shooting Scottish Gorse.

 

Andrea and Scottish Gorse T1605022910.jpg

 

(Nikon D3200 with internal Baader-U, Tamron 21 mm f/4.5. And this being Scotland, some rain drops were encountered as well :D )

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I still find it curious how yellow petals often appear yellow in reflected UV images as well.

 

That Gorse looks like an unfriendly kind of plant who doesn't like to be touched (are those spines or just needles (leaves)?).

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Mark, it is odd, but of course they often are not all yellow (in the bullseyes for example). I have also seen yellow sunflowers go green. It has to be a side effect of the Bayer dyes though.
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Many thanks for comments.

I was thinking just the same about the yellow. I assume it is just co-incidence - that is this flower has two peaks in its reflected spectrum, one at visible yellow (about 550 nm?) and one around 360 nm (based on Steve's wonderful image http://www.ultraviol...dpost__p__19165 )

(Or is it more likely that the yellow is not a pure spectral colour by caused by stimulation of red and green sensitive cones in the visible, but a similar principle would apply?)

Presumably someone will have measured something like this with a spectrophotmeter ?

 

As we can't see 360nm we could presumably show it as any colour (as discussed elsewhere)

 

This is the BGR version.

 

post-175-0-68187200-1517153198.jpg

 

As I was curious about this I picked up a few yellow things while out walking the dog: some catkins and yellow leaves (ivy I think). Same settings as above. Here is visible then UV with normal and BGR. The images speak for themselves I think. I am probably not going very deep into UV - so I am sure could look different, but shows the point that visible does not predict UV:

post-175-0-30576700-1517153444.jpg

post-175-0-45016600-1517153453.jpg

post-175-0-69125400-1517153462.jpg

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The catkins are from a Hazel Corylus avellana. Not sure about the leaves, they might be from the flowering shots of a Hedera (Ivy).
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You have to be careful around here! Soon you will start picking up Latin names for everything!!

 

I love the rich yellow Gorse flowers on rainy days.

 

Thanks for showing us your indoor experiment.

 

The R/G/B channel colours in which your camera records under a UV-pass filter are a by-product of the Bayer filter dyes. The false colours presented in your converted JPGs are a by-product of whatever channel swaps you perform or whatever area of the photo you click on with the white balance tool. There is no "right answer" here. You are free to choose what you like to present. (((((....unless you want to make a formal presentation in the botanical section where we require a standardized look....and we do encourage everyone to add their floral UV-signatures there if a proper id can be made....we will help if we can.)))))

 

 

The yellow of the Gorse flower is likely due to flavonol pigments.

 

Reference added later:

Chemical Dictionary of Economic Plants

Jeffrey B. Harborne, Herbert Baxter

John Wiley & Sons, Aug 30, 2001

 

The yellow pigments are a mix of 3 chalcones and 2 flavonols.

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I was surprised that searching on scotch broom versus gorse turned up an actual answer: Both are in the Pea Family and have similar yellow flowers but Gorse has "rigid spines".
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I was thinking just the same about the yellow. I assume it is just co-incidence - that is this flower has two peaks in its reflected spectrum, one at visible yellow (about 550 nm?) and one around 360 nm (based on Steve's wonderful image http://www.ultraviol...dpost__p__19165 )

(Or is it more likely that the yellow is not a pure spectral colour by caused by stimulation of red and green sensitive cones in the visible, but a similar principle would apply?)

Presumably someone will have measured something like this with a spectrophotmeter ?

 

As we can't see 360nm we could presumably show it as any colour (as discussed elsewhere)

 

White balance, like with visual, aims to neutralize the color cast or color temperature so that grays look gray, white looks white... so there is no color cast.

White balance can just as well be called gray balance.

So given a neutral color balance, then grays in UV represent a uniform UV reflectance.

Keep in mind we are white balancing a narrow spectrum, given that 320nm to 400nm is about the same width as red, blue, or green. Try white balancing an even narrower bandpass range sometime...

Getting to my point, the yellow from the flower in UV means that the Bayer is not seeing any blue, and some mix of green and red. So the flower is not reflecting any 370nm-400nm.

Of course you can white balance the shot alternatively or non-neutrally, but then you will have a color cast.

Yellow in UV means there is no reflected 370nm-400nm, and nothing below 350nm either. Basically.

Indeed the color that the Bayer sees is accidental, not intended, because the Bayer isn't intended to record anything in UV or IR, just 400nm to 700nm.

Regardless of that, it does, or we would not be here.

 

More on all this:

http://www.ultraviol...20%20uv__st__40

 

This shot shows how U-340 4mm thick has no 370nm-400nm (blue), and how the 330nm filter has no 350nm+ (red or blue), white balance in this photo was done on the PTFE holder.

This is not reflected light, delineated 340nm reflected UV (green) is hard to find in a 320nm to 400nm filtered shot.

post-87-0-56476200-1517376908.jpg

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the yellow from the flower in UV means that the Bayer is not seeing any blue, and some mix of green and red. So the flower is not reflecting any 370nm-400nm.

Yellow in UV means there is no reflected 370nm-400nm, and nothing below 350nm either.

 

We must be careful when extrapolating from a stepped filter board to an actual UV-signature because the reflectance chart for flowers typically does not have sharp shoulders or "stepped" peaks. For example, the yellow, UV-reflective tip of an outer Dandelion ray has a UV-peak at 350 nm. But the shoulders on that peak are rather gentle reaching between 300 - 400 nm. So while not at peak strength, there is still UV-reflectivity between 370-410 nm and under 350 nm. After 410 nm, blue and green are (obviously) absorbed. At about 500 nm the reflectivity begins to rise again to produce visible yellow.

Link: http://www.reflectan...corollaless=161

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