• Ultraviolet Photography
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Here's one for you to try

10 replies to this topic

#1 Andrea B.

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Posted 27 January 2020 - 22:10

Make a visible photo of a/some flower/s under mixed light containing UV (such as sunlight)
and then under ONLY visible light.

Some flowers having strong UV-induced visible fluorescence should show a difference, shouldn't they?

You'd probably want to use a visible LED for this with an additional strong UV/IR blocker.

I'm just curious.
Andrea G. Blum
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#2 Bernard Foot

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Posted 27 January 2020 - 22:40

I'd have guessed that the UVIVF is never going to be noticeable in visible light that is strong enough to photograph in. But I stand to be corrected.

Another approach might be to take a UVIVF shot and a visible shot and stack them in some way.
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#3 OlDoinyo

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Posted 28 January 2020 - 02:05

Are you proposing obtaining a fluorescence image by subtraction?? I am not sure I understand why.

#4 dabateman

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Posted 28 January 2020 - 06:08

Yes lighting matters.
Andrea might just be after the different in camera colors.
However, due to the loss of lower wavelengths in the visible only. Then the petals of such flower will seem less crisp. I like the crunchy sharpness UV gives to flowers.

#5 Andrea B.

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Posted 28 January 2020 - 08:56

I may not have explained that well.

Make first visible photo under UV + Visible illumination.
Make second visible photo under Visible illumination only.

In both cases a UV/IR blocker is on the lens.

If the UV induces some visible fluorescence, then it is possible the vis fluor intensifies or slightly alters a color in the subject being photographed. And that intensification or alteration would be noticeable when compared to the second photo having no visible fluorescence.

As a quick experiment I looked at marks made with my fluorescent highlighters under combined illumination from my Nichia 365nm UV-Led torch and a Visible LED torch. The marks were indeed less colourful after the UV torch was turned off.

It would be difficult to perform this experiment in natural sunlight though. Because how would you prevent the UV in sunlight from reaching the subject? I suppose a large UV blocking Filter Dome could be placed over the subject. OK, now this is getting crazy.....
Andrea G. Blum
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#6 Stefano

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Posted 28 January 2020 - 13:45

View PostAndrea B., on 28 January 2020 - 08:56, said:

I suppose a large UV blocking Filter Dome could be placed over the subject. OK, now this is getting crazy.....
Like using a Dome of UV pass filter glass to make UVIVF shots outside, under the sun. It could be done for very small subjects using an incandescent blacklight envelope, cut to a Dome shape. But you would need to remove the IR contamination...

#7 dabateman

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Posted 28 January 2020 - 16:25

A large polycarbonate plastic box or sheet could work. Or a difuser screen. Take image in direct sun light, with subject with and without the diffuser.

A bed sheet might also work. Not sure how much UV passes through cotton. Uv does pass through polyester.

#8 Andrea B.

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Posted 28 January 2020 - 17:26

Stefano, I don't think the IR would cause problems. It would be very uncommon for the IR to induce visible fluorescence in typical outdoor subjects being photographed.

David, yes if polycarbonate or UV-blocking window glass were used as a box top, that could work. (Box could have cardboard or wood sides.) Finding known transmission of the poly or glass might be iffy. Like, if I just go over to Home Depot or Lowes, I'm not sure I would find materials accompanied by transmittance charts. This comes full circle to my ever increasing "need" for spectroscopy gear.

(Now I've gone blank. Do we call it spectrometric gear or spectroscopic gear. Oh well. Look it up, Andrea B.)

Well, currently there are so many other things to do. And I'm not sure this experiment is all that interesting.

Well, it is, to me anyway.....but there are so many other things to do.
Andrea G. Blum
Often found hanging out with flowers & bees.

#9 Stefano

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Posted 28 January 2020 - 20:11

View PostAndrea B., on 28 January 2020 - 17:26, said:

Stefano, I don't think the IR would cause problems. It would be very uncommon for the IR to induce visible fluorescence in typical outdoor subjects being photographed.
Yes, forgot that. You don't need pure UV if you have a UV/IR cut filter on the lens.

#10 Damon

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Posted 29 January 2020 - 05:42

I am interested in this experiment. It may add a clue to why UVIVF occurs at all.

I wonder if flowers that fluoresce brightly also emit more heat during the day. Some insects can detect heat changes very well.
The dark UV signature in the center of a Gazania for ex is warmer than the outside petals. I saw this with a laser thermometer. Maybe UVIVF adds to this so the total flower heat emission is higher than surrounding flowers without these characteristics.

In the morning these early extra heating flowers attract the first insects that come flying around. Insects also need heat to get moving around faster too so a win win in a bunch of ways.

Or maybe all these nights with UV lights is finally getting to my brain.

#11 Cadmium

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Posted 29 January 2020 - 06:43

Damon, You mean why UVIVF occurs in flowers? Not everything, right?
As far as heat, indeed some flowers and such, probably retain more heat because of the insulating dead air space in their structures.
Here is a low res example of heat retained in a few flower structures.
Well the dandelion isn't exactly a flower anymore in this shot, but still retains more heat than other material surfaces in the photo.

Attached Image: Flower_Visual_vs_FLIR.jpg

Edited by Cadmium, 29 January 2020 - 06:44.