23 replies to this topic

[bobfriedman]

So I was doing some painting with light and figured I would try some UV stimulated resonance fluorescence into the visible. (Yes.. I did see Andy's nice work)

Nikon D850, AF-S VR Nikkor 200/2G
25s f/13.0 at 200.0mm iso31


Nikon D850, AF-S VR Nikkor 200/2G
61s f/13.0 at 200.0mm iso31

[colinbm]

Beautiful images Bob.
Could you talk about it all a bit more please.....

[bobfriedman]

not much to discuss really.. both images in a dark room the first image illuminated with a visible torch to paint in the subjects... the second identical setup but with a Nichia torch with a U-340 filter.

folks here call this UVIVF

Edited by bobfriedman, 25 November 2020 - 01:12.

[bobfriedman]

as far as painting with light (all visible like the first image), you might check this link..

https://haroldrossfi...and-techniques/

[Andy Perrin]

Gourd-ous!

They look like ducks to me.

[Cadmium]

Bob, Looks great!
They reminded me of ducks also. Three ducks, the one in the middle either sleeping or not doing too well...

[Stefano]

I like how especially the first gourd on the left has two colors with a sharp transition.

Nice images overall, both visible and fluorescence.

[dabateman]

Andy Perrin, on 25 November 2020 - 01:26, said:

Gourd-ous!

They look like ducks to me.

After you said ducks, I now see the left and right arguing over whom killed the middle one.
Great composition.

[Andrea B.]

Bob, you make such good photos.

Wondering why gourds fluoresce? Are they coated with something?

[Stefano]

Andrea B., on 25 November 2020 - 20:00, said:

Wondering why gourds fluoresce? Are they coated with something?

Well, pretty much anything fluoresces under UV, except for (in my experience) water (and snow) and air. There could be hundreds of different chemicals responsible for the fluorescence, and finding them is not easy. Unless you use a spectrometer, it is almost impossible.

(I don't think a coating is the reason of the fluorescence, but it may play a role).

Edited by Stefano, 25 November 2020 - 20:16.

[Andrea B.]

Nah, not all that much is fluorescent.

.....arguments to the contrary always welcomed, of course.....
I'm always willing to be proved wrong.

I have a gourd like the left one in Bob's photo. Its green area seems to fluorese slightly red (chlorophyll?), but the orange neck not much at all.

[Andy Perrin]

Andrea, I’m not sure why you are saying not much fluoresces? My experience has been more like Stefano describes. Definitely the brightness varies considerably though.

[Cadmium]

Yep, almost everything fluoresces. Some. It is hard to find things that will not show some fluorescence when illuminated by a UV-only torch. Example:
Here is brown cardboard, but even black rubber can fluoresce, depending. The illuminated area on the right is 100% fluorescence.

[Andrea B.]

Definitely the brightness varies considerably though.

Yep.


It's easy to confuse the reflection of the emitted light off non-fluorescent parts of a subject as fluorescence.
But I still don't think that all that many things fluoresce.

The green parts of my gourds seem to fluoresce a little bit red from the chorophyll. The yellow/orange carotenoids do not fluoresce under 365nm IIRC. I think you need a much lower wavelength to induce some UV fluorescence in carotenoids. (Look up??) Anyway, that's neither here nor there, it is just that the cyan fluorescence in the second photo in the first post has me a bit baffled.

[Cadmium]

Your not looking for brightness, you are looking for purity. Any added brightness is from visual rang light, you want that removed.

Almost everything fluoresces some. Hard to find anything that will not show some dim florescence.
Put your UV glasses on, turn off all your lights, and go around looking for anything that will not show some light when you point your UV torch at it.
Of course, some of that will be dust, but look at the material, something clean and something black.
Everything...
You said I could disagree.

Why is the cyan baffling?

Edited by Cadmium, 01 December 2020 - 06:07.

[Andy Perrin]

Yeah, when you have eliminated all visible light from the torch, any other light you are seeing is coming from fluorescence of SOMEthing. It's true you can get one material fluorescing and an adjacent one reflecting it, but that doesn't mean it's not also fluorescing (although it may be hard to work out what color).

[Andrea B.]

Why is the cyan baffling?

I have a bunch of gourds here. Some like in the photo. No cyan fluorescence. A bit of red fluor from the green areas.

[Andy Perrin]

Andrea I have two gourds and one of them has developed cyan stripes over the course of the last month. I would suggest that the cyan might be due to a mould or fungus on the surface (and maybe not very visible to the eye without fluorescence).

[Bernard Foot]

Beautiful photos, Bob. The similarity to a group of birds has just got to be intended!

What I don't understand, and I don't think is covered in the discussion above, is why the dark blue/green areas of the "dead" duck and its murderer on the right are so different under fluorescence. Is it what Andy says - the gourds are of different ages and one has started growing a fungus?

[bobfriedman]

Bernard Foot, on 03 December 2020 - 09:36, said:

the gourds are of different ages and one has started growing a fungus?

no idea.