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Frozen outdoor


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Two frozen outdoor UVIVF scenes while we still have darks here. Both with 105mm f/4 @ f/9, 30s ISO 100 and UV- painted with a Tank007 TK-566 UV-LED light with a ZWB1 2mm thick filter on the front and an L39 filter on the lens. The tree fell by itself a sunny quiet summer day, infested by carpenter ants, but the stub was later trimmed.

 

 

2018-05-02-0141E-7197-md.jpg.ebc56458c22a32cccf63bdbe679b7cf2.jpg

 

 

 

I was surprised to find UVIVF in what looked like clear thin sheet of ice crystals in visible light.

 

2018-05-02-0143E-7198-md.jpg.f11552a67bb42e4518cc3da3c4b0a174.jpg

 

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Andrea B.

Very interesting. There are all kinds of fluorescent activities in the first one.

Seems like the carpenter ants might have killed their host and food item. Not a particularly good adaptation by them, I'm thinking? But perhaps the the carpenter ants simply took advantage of an already weakened tree? Hard to know, I suppose.

 

I have a Question for Øvind or anyone who can answer it: In the ice crystal photo, has the crystal possibly refracted the UV light and changed the wavelength so that the blue occurs because of refraction and not because of fluorescent emission? I'm just being curious.

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Andy Perrin

Refraction can’t change wavelengths. It can separate different wavelengths that are already there but it can’t make new ones.

 

I would like to know if the visible light from the source is being well-blocked though?

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Andrea B.
Why do they say that then? That the frequency remains constant but the wavelength changes? I R confussssed.
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Andy Perrin
They don’t say that. Frequency is c/wavelength (c is speed of light which is constant In air but not in the material which is where I think you are getting confused). You have light with one mix of wavelengths coming in and (mostly the same ones) coming out just in different physical locations. This neglects absorption but I’m talking about transparent coatings in leaves.
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Andrea, the tree was dry and dead when I first moved into the cabin many, many years ago, so unlikely that ants were guilty of killing it. It was joined together at the root with a dead neighbor tree that fell a few years ago, and since they were tilting in different directions I was waiting for this one to go down, actually looking out that it would not hit me on the way to the outhouse(!). It survived some recent severe winter storms, so it was surprising when it fell on such a quiet summer day.

 

Judged from how light was emitted from an object like a white dinner plate (my previous "some foods" thread, weak purplish emission) and intensity of the presumed fluorescence from the ice relative to nearby objects, I think it is unlikely that the majority of the blue color on the ice is due to inadequate visible light filtering on the UV source. Notice how black the small tree trunk in the frame is. There could perhaps be something in the water like suspended microorganisms or humus ? This was ice on a melt water pool so there are many possibilities although it looks clear. I regret I forgot to do visible light shots at the time documenting how transparent and smooth the ice was, but I now just went outside and took some sunlit visible hand held shots of both (this time without the ice present) and I will complement for the record once I processed them in the evening, and perhaps also try a UVIVF capture with unfrozen water.

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Andrea B.

That was interesting, Øvind. The ants were being opportunists then. The tree was damaged or dead and the ants were able to move in. Yes, that would be a bit frightening that the tree fell over on a quiet summer day. I have fanciful visions of a squirrel giving it just one push too many. :)

 

Or perhaps there could be dissolved minerals in the water?


 

Andy, I had gone to review Snell's law, etc. and found the attached assertions about wavelengths that simply make no sense to me given the reciprocity of wavelength/frequency (and which we recently reviewed somewhere else on UVP.) I must be misreading them somehow which is why I asked the question above. What can these websites mean when they are writing that "wavelength changes"? It seems very misleading. If you Google "refraction changes wavelength", then you will see more examples. Halp!! And thank you in advance.

 

Apologies to Øvind for going off topic on his post, but we do tend to do that a little bit on UVP because we are all so interested in so many different science and engineering topics in addition to our photography interests.

 

Screen Shot 2018-05-05 at 8.48.55 PM.jpg

 

Screen Shot 2018-05-05 at 8.50.58 PM.jpg

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Andy Perrin

Andrea, the statement is correct, you're just missing the fact that when the light LEAVES the material, the wavelength changes BACK to what it was before. Light hits the material at an angle, the wave slows down in the material so wavelength gets shorter (frequency stays constant) inside the material, and the light changes direction, but then the light leaves the material and the wavelength gets longer again, reversing the change in wavelength, but the direction is usually still altered unless both the material surfaces are parallel (as in a sheet of glass).

 

Since we are in air and taking photos in the air, we would not see any change in the wavelength from out here, although we could potentially observe the light having its wavelengths separated out spatially, like in a prism. I'm not seeing any rainbow colors here, though.

 

From this site:

https://www.school-f..._refraction.htm

 

This illustration shows what I'm saying pretty well. In this case, the two surfaces of the material are parallel, so the light gets shifted parallel to the original beam but the ultimate direction is the same as the initial direction, despite the change inside the material.

post-94-0-63038900-1525574860.jpg

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Andrea B.

Whew, thank you for restoring my physics sanity.

You're right, I was not letting that light leave the refracting medium. I was stuck in the middle of it myself. :lol: :lol: :lol:

We can get hung up on the most obvious things sometimes. (Well, I can anyway...)

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Here comes the promised reference captures in visible light but also see new UVIVF capture and comment further down.

 

Looks like there is some chlorophyll on the tree stub:

 

2018-05-05-1453E-7200-md.jpg.f2b7b25a9e90148e639fce417a958932.jpg

 

 

The water level in the meltwater puddle was slightly lower now:

 

2018-05-05-1453E-7201-md.jpg.93506ce1a30691756355986b06d28ca9.jpg

 

 

Now after all this discussion about the potential fluorescent properties of ice, I just went outside to have a new look in the dark. Nothing was now frozen on the puddles, but the bluish-pastel green fluorescence was still present (it was leaning slightly more to the green to the eye than in the captures with daylight WB) on all the meltwater puddles, not only the one in the original capture. First a visilbe light reference shot (Nightrider 200 lumen LED bikelight light source); I included some melting snow to have some reflective frozen stuff:

 

2018-05-06-0057E-7205-md.jpg.549794539bdaca5479a5ef3c5bcbc9aa.jpg

 

 

Then the UVIVF captured same way as above, 30 sec exposure f/9 ISO 100, UV-LED light at about 0.5m distance lighting most of the frame simultaneously:

 

2018-05-06-0058E-7206-md.jpg.7ed139e33d5df6c65782c011b1fa4faa.jpg

 

 

The blue color of the snow is mostly due to light from the night sky, as it is not completely dark at night here any longer. Here the UV LED light is off to capture the background light with the same exposure:

 

2018-05-06-0059E-7207-md.jpg.cff64815e6d607991f2b6fee06d54934.jpg

 

 

To conclude there is something in the melt water everywhere causing a milky pastel blusih-slightly green fluorescence. Perhaps it could be algae?

 

 

BTW, I think we are rapidly approaching summer here - the first mosquito was out today, but none captured - dead or alive. (We have two species overwintering as adults here).

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Andrea B.

Nice follow up investigation to the original photos. And the ice water is definitely fluorescing to me. It's very pretty in the snow/ice photo (#4).

 

I suppose the only question might be "what colour" is that fluorescence? I mention this because there has been an ongoing conversation about white balance in UVIVF photos. (And whether there is violet/blue leakage from our lights or filters). But I don't want a colour question to get in the way of the fact that this ice is fluorescing. So don't get me wrong when I ask what white balance were you using? B) Just curious.

 

Given that we use such broadband filtration when making our UVIVF photos, it is often useful to judge the brighter areas in comparison to the rest of the scene so that reflected glow is not misjudged as fluor. In photo #4 it is obvious what is fluor and what is not. The little bits of fluor from the twigs and grasses support the ice fluor.

 

(Of course you saw this with your own eyes. Let's not forget that.)

 

Why not shoot some ice cubes from the refrigerator to use as a comparison? You could shoot them indoors in the dark or take some outside and place into the scene. Might possibly be an interesting follow-up, do you think?

 

More than I ever wanted to know about water: http://www1.lsbu.ac....l_spectrum.html

This link has water's absorption spectrum and contains many reference links.

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Andrea, thanks for your comment, especially on the colors, however I need to correct you on one missed point: The water in the last UVIVF capture was not frozen, I should perhaps have made that clearer (and the title initially chosen for the thread is a bit misleading now). So this just demonstrates that it was not the ice structure that caused fluorescence (although that would have been a nice finding), but something in the water, whether algae, microorganisms or minerals/silt. (The state of the water did not matter, except for providing some nice structure to the surface when it is in the form of ice.) With respect to the latter possibility I would think that we then would have seen some fluorescence in the surrounding ground, but I might have to seek out an area with less organic coverage and exposed silt to see what is going on there. Also I might want to check out what the water in the our local lake/pond is doing. It is a brown water lake with a lot of humus in it.

 

The white balance was set to daylight, which could explain why the captures was on the blue side compared to the blue-slighlty green pastel that appeared to the eye.

 

I think color balance is a tricky question. If the purpose is to compensate for the light leakage (and possible other background light), it is possible that the approach used in astrophotography would be better ( https://clarkvision.c...ge.processing2/ ): To obtain the most correct colors a daylight white balance is used during capture. During processing the light pollution is subtracted by adjusting the left edge of the histogram for the background to match between color channels. This is because the colors of the stars are not going to change when light pollution changes. Light pollution is an addition that need to be subtracted from the signal. In contrast to this adjusting white balance would be a multiplication process that affects both light pollution and the signal and would give incorrect colors on the stars. UVIVF is also emitted light so this should be pretty similar to the astophoto situation. However the problem would then be to estimate how much to subtract in a UVIVF situation. The ideal test for that could be to have a white object with zero fluorescence if such a thing exists. Instead of applying a white balance to it, one would do a color channel specific histogram shift to subtract the light leakege and any other background light. I the last UVIVF test, both light leakage and the light from the sky could be possible light pollution sources.

 

As an experiment, let us assume the color of the snow is not due to fluorescence but only light leakage from the UV light and background light from the night sky (even if this might not be correct). I marked a small crop in the upper left corner on the snow and adjusted levels on the color channels so that the histograms match, primarily on on the left side (a slight adjustment to general exposure level was also done before this). Screen shots before and after the adjustment. Both blue and green channels had to adjusted in different amount to match the red channel (note that I had also selected an alternative crop that was not used):

 

Levels-adjustment-UVIVF-color-corr-000.jpg.ffb02e4ba2edcedf7f1c1babfaf3b375.jpgLevels-adjustment-UVIVF-color-correction-001.jpg.af567ce4a4b30813b036317cedbeb068.jpg

 

 

 

When the crop is removed to reveal the whole frame this is what I get - I thought there was going to be more color shift in the water. Perhaps it was my eyes that were tricked to think it was greener as they might have "whitebalanced" to the bluish color of the night sky.

 

2018-05-06-0058E-7206-level-subtract-md.jpg.601ac59969f3a555070328ae6329955c.jpg

 

 

But again, we would have liked to have a better white non-fluorescent standard than snow.

 

 

Added: I just retrieved a water sample from the local brown water lake and it had the same milky UVIVF appearance. In visible light the color to the eye of a small sample against a white background is slightly brown. I also check some exposed silt outside after dark, and there was almost no fluorescence from it so local minerals in the water are likely ruled out as the fluorescent source.

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Andrea B.

Øvind, thank you for this interesting and useful discussion of white balance in fluorescence photographs. With your permission, I would like to excerpt some of it for inclusion in the Sticky :: White Balance in UV/IR Photography . Would that be OK? I am referring to the per-channel histogram adjustments you illustrate.

((I corrected my comment to read 'water' instead of 'ice'.))

 

To obtain the most correct colors a daylight white balance is used during capture.

When working with UV Innovations Grey Target, a fluorescent "grey card", I found that fluorescent white-balance required a higher temperature than daylight, 13000-15000K in some examples. But the Grey Target is calibrated to certain standards, so I can't make any safe generalizations because I am not using the suggested filter and peak wavelength (fairly close though). But -- perhaps you could experiment with a higher K temp WB setting?

 

.....a color channel specific histogram shift to subtract the light leakege and any other background light.

I'm going to try this on some of my fluorescent photo sets.

((And I suspect that Andy P, when reading this, will also know how to accomplish this kind of subtraction in MatLab !!))

 

The ideal test for that could be to have a white object with zero fluorescence if such a thing exists.

LabSphere says that Spectralon (clean, uncontaminated) does not fluoresce. However, apparently PTFE can fluoresce as several photos here on UVP have shown. So I'm going to go find my Spectralon photographed under 365 UV-Led and learn from that how to make the histogram adjustment you show above.

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Hi Andrea,

Thanks for your kind response. I am of course happy if anything I contribute can make it into the stickies. May be hold off a little; I worked last night on a more systematic write-up intended for a new thread on the theme (It is best to not hide this information in a general image thread). I also did some more tests late last night, experimenting with standard visible targets, but need a little time to process and put it together with the results. Once I get that new thread posted may be tonight, I suggest we continue the discussion there.

 

Looking for a non-emitting standard can be tricky. However if one has a perfectly filtered setup if such a thing exists (pure UV from illumination source, no UV or IR getting though to the camera) it should be possible to test as the ideal target would be white in visible light and completely black in UVIVF if there are no other emitting objects around that can reflect off the target. It would be nice if you would experiment with that at your end until I get the new thread up as my choices of filtration are very limited.

 

Relevant to the melt water subject of the current thread, I also did try a couple of UVIIF exposures of the puddles last night, but not surprising it did not emit anything in IR worth showing (recorded with my D40x IR-720nm converted body).

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Andrea B.

Øivind, take your time. I know it is hard to prepare a long post when working full time. We will all be looking forward to a your write-up about adjusting for background/leaked light.

 

The big problem is that these UV LEDs we are all using do seem to emit some small amounts visible light so require strong some filtration. But I don't think the white Spectralon photographs black in my UVIVF set-ups. So I'm just not sure what is leaking where. I will experiment further.

 

 

 

Edit: strong -> some

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With the Spectralon standards there cannot be, I would expect, any fluorescence from the target itself. However, it is so difficult to control that nothing else in the neighbourhood of the object being photographed is fluorescing, that light from fluorescence elsewhere in the neighbourhood of the target may be what is being "seen" reflected from the target. With PTFE slabs, I have noticed recently in one case that what looked like PTFE fluorescence was coming from a box I had put under it. In other words quite a lot of UVA was transmitted through the slab (a thin one, just 2 or 3 mm thick), enough to excite strong flourescence and the blue fluorescence from the box transmitted back through the slab. I realised this because I could see through the slab, in the fluorescence, a drawing printed on the box. Putting a black cloth under the slab almost eliminated the fluorescence.

 

This does not rule out the question about the radiation emitted by the UVA LEDs being what the camera is detecting. Yesterday, already before reading this thread, I measured the emission spectrum of my filtered Convoy 2+. There is still a small amount of violet light coming through: 0.14% of the photons are from wavelengths longer than 400 nm. By the way the peak is at 366.8 nm.

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Andrea B.

Pedro, thanks for that measurement of the Convoy. I hope it does not come as a surprise to any readers that a UV-LED torch outputs some visible violet light. We've been trying to make this known for a while now. But it is cool to have another actual measurement of a filtered Convoy torch!!

 

It seems your filtration has cut the visible leak down to a just a tiny amount. But you don't say what filtration you were using?? May we please know?

 

It is so difficult to control that nothing else in the neighbourhood of the object being photographed is fluorescing

Yes, indeedy !!!!

 

That drift off the peak 365 nm is not at all bad. I can't imagine that there would be anything at all different between a fluor photograph @ 365 nm versus one @ 366.8 nm. B) The absorption charts I've seen (so far!) for various substances are never single-spiked.

 

 

 

EDIT: Added "another" to "actual measurement" which I though I had done but didn't !!

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enricosavazzi

Andrea, the statement is correct, you're just missing the fact that when the light LEAVES the material, the wavelength changes BACK to what it was before. Light hits the material at an angle, the wave slows down in the material so wavelength gets shorter (frequency stays constant) inside the material, and the light changes direction, but then the light leaves the material and the wavelength gets longer again, reversing the change in wavelength, but the direction is usually still altered unless both the material surfaces are parallel (as in a sheet of glass).

 

Since we are in air and taking photos in the air, we would not see any change in the wavelength from out here, although we could potentially observe the light having its wavelengths separated out spatially, like in a prism. I'm not seeing any rainbow colors here, though.

 

From this site:

https://www.school-f..._refraction.htm

 

This illustration shows what I'm saying pretty well. In this case, the two surfaces of the material are parallel, so the light gets shifted parallel to the original beam but the ultimate direction is the same as the initial direction, despite the change inside the material.

post-94-0-63038900-1525574860.jpg

An interesting consequence of the change of light speed is that, in a medium like water, it is in principle possible for something else than light (e.g. electrons or other particles) to travel faster than light does in the same medium. This is not a violation of special relativity, because the universal speed limit is the speed of light in vacuum. Cerenkov radiation is emitted when something travels faster than light in a specific medium. This is seen e.g. in the water pool of nuclear reactors, which glows blue in proximity to the reactor core. Most of the emitted Cherenkov radiation is in fact in the UV, and the radiation spectrum is continuous (no emission lines). In theory at least, a nuclear reactor immersed in water would make a fine UV source for our photography and spectroscopy.

 

Another consequence is that electromagnetic radiation of different wavelengths is slowed down by different amounts when entering a high-dispersion medium like water.

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Cerenkov radiation is emitted when something travels faster than light in a specific medium. This is seen e.g. in the water pool of nuclear reactors, which glows blue in proximity to the reactor core.

Enrico,

I have actually witnessed this with my own gelatinous orbs!

1978 Tennessee Junior Science and Humanities Symposium, toured the Oak Ridge National Laboratories.

They turned off the lights as we looked into the pool of the Californium High Flux Reactor.

As I recall we weren't allowed to take photos.

Thanks for the memory bump!

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An interesting consequence of the change of light speed is that, in a medium like water, it is in principle possible for something else than light (e.g. electrons or other particles) to travel faster than light does in the same medium. This is not a violation of special relativity, because the universal speed limit is the speed of light in vacuum. Cerenkov radiation is emitted when something travels faster than light in a specific medium. This is seen e.g. in the water pool of nuclear reactors, which glows blue in proximity to the reactor core. Most of the emitted Cherenkov radiation is in fact in the UV, and the radiation spectrum is continuous (no emission lines). In theory at least, a nuclear reactor immersed in water would make a fine UV source for our photography and spectroscopy.

 

Another consequence is that electromagnetic radiation of different wavelengths is slowed down by different amounts when entering a high-dispersion medium like water.

 

Thanks for interesting information. The last sentence made me associate and wonder: Ten years back I bought one of those Steripens for an Africa trip. (As I recall it is based on a mercury tube.) When active it will in addition to UV emit a pale blue visible light. A sensor switch only allows it to be on with the tube submerged. The manual states that the emitted UV will not pass from the water to air. I have some trouble believing this really true? Should I wear UV protection glasses when using it?

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The manual states that the emitted UV will not pass from the water to air. I have some trouble believing this really true? Should I wear UV protection glasses when using it?

In some situations , yes you should. especially when the water surface is directly visible. See some pictures in the article below.

https://www.scienced...47789391500174X

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Thanks for the reference, Ulf, interesting. Better watch from the side of the bottle then. Perhaps it is wise to wear gloves when holding the Steripen to be on the safe side?

 

 

I have now opened a dedicated thread on the light pollution subtraction technique:

https://www.ultravioletphotography.com/content/index.php/topic/2735-thoughts-on-color-correction-in-uvivf-by-subtraction-rather-than-white-balancing/

Let us continue the discussion on that part there.

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Pedro, thanks for that measurement of the Convoy. I hope it does not come as a surprise to any readers that a UV-LED torch outputs some visible violet light. We've been trying to make this known for a while now. But it is cool to have another actual measurement of a filtered Convoy torch!!

 

It seems your filtration has cut the visible leak down to a just a tiny amount. But you don't say what filtration you were using?? May we please know?

 

It is so difficult to control that nothing else in the neighbourhood of the object being photographed is fluorescing

Yes, indeedy !!!!

 

That drift off the peak 365 nm is not at all bad. I can't imagine that there would be anything at all different between a fluor photograph @ 365 nm versus one @ 366.8 nm. B) The absorption charts I've seen (so far!) for various substances are never single-spiked.

 

Yes, 668 nm is very close to 665 nm! :)

 

I am afraid I do not know what the filter is... When I bought my Convoy 2+ from an Aliexpress seller, I ordered the filter from the same seller without noticing that the description was lacking details. The filter was described as: "365nm Special optical materials UV Flashlight Visible Filter Lens". :(

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Not that I mind, and light leakage is relevant for the present thread too, but it looks like another thread crossed into this one?

 

Edit: Reviewing the thread I now so that the Convoy was mentioned earlier in the thread so that was the confusion. it is always nice to have the freedom of diving into details as they appear along the journey.

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