Questions about UV fluorescent photography

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MarkSturtevant
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Questions about UV fluorescent photography

Post by MarkSturtevant »

I had been attempting to photograph some of the things I've seen while going out at night with a UV flashlight. But I have an issue that is probably a trivial matter to those with more experience and better equipment. Two pictures will suffice. Lou Jost especially comes to mind as someone who could really help out here.
First off, here are aphids under regular light.
ImageAphids in regular light by Marcoli Sturtevantione, on Flickr

At least some aphids will fluoresce under UV. This species (the poplar tree aphid) glows a lovely color that is pretty similar to how scorpions fluoresce, which is interesting, and I think the picture below shows that reasonably well. A minor issue here is that the aphids are blurred because of the longer exposure time and the aphids were moving a little.
But the main issue is with the leaf. As expected, leaves glow a deep red color with my UV flashlight. But in all my photographs with leaves, their colors come out wrong, as you can see. I am wondering why that is.
ImageAphids in UV light by Marcoli Sturtevantione, on Flickr

There are likely two issues that I am having.
One is that because the flashlight is one of those inexpensive (cheap) LED UV flashlights, it probably emits other colors besides those in the desired UV range. But the fluorescent colors that I see don't seem wrong, and so I suspect that is not terribly important here.
The second issue, however, is that the leaves are probably reflecting a lot of UV light, and that is getting to the camera sensor. Now camera sensors are supposed to have a UV filter coating (don't they?), but I've read that they are not always able to block UV entirely. This seems reasonable here since the reflected UV was probably rather intense, what with it being so close and the long exposure and all. I am not sure why that would show up as purple here, but that is in part why I have questions.
If that is correct -- that the main problem is reflected UV light getting to my sensor -- then it seems likely the best solution it to get an effective UV filter on the lens.
Is this the right thinking? There is quite a price range on UV filters. I am hoping that a pricey one is not strictly necessary.
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Scarodactyl
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Re: Questions about UV fluorescent photography

Post by Scarodactyl »

My guess is that shorter wave UV us blocked but near violet long wave is not. A longpass filter might fix it but it may take some experimentation.

Pau
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Re: Questions about UV fluorescent photography

Post by Pau »

Putting short pass filters at the UV flashlight will improve a lot your results. Best ones are expensive but if the size matches Chinese ZWB2 are very affordable and convenient.
Emission long pass filters for the camera/eye side are also recommendable (for the eyes wear protective glasses, any eyeglasses made of polycarbonate are effective). Generic UV camera filters I have tested are of low utility, although likely there can be better ones. The old style Nikon L39 is useful but not very efficient.
Which flashlight you have? I have the Convoy S2+ Nichia 365nm with ZWB2 filters and they are inexpensive an work very well.
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Re: Questions about UV fluorescent photography

Post by MarkSturtevant »

Pau wrote:
Sun May 29, 2022 1:26 am
Putting short pass filters at the UV flashlight will improve a lot your results. Best ones are expensive but if the size matches Chinese ZWB2 are very affordable and convenient.
Emission long pass filters for the camera/eye side are also recommendable (for the eyes wear protective glasses, any eyeglasses made of polycarbonate are effective). Generic UV camera filters I have tested are of low utility, although likely there can be better ones. The old style Nikon L39 is useful but not very efficient.
Which flashlight you have? I have the Convoy S2+ Nichia 365nm with ZWB2 filters and they are inexpensive an work very well.
Thank you both.
The flashlight is from a company named STIALO, and it does not have a fancy name like yours. Here it is: https://www.amazon.com/gp/product/B0796 ... UTF8&psc=1 It will be a given that it will have emission peaks other than 365nm, but it sure does make things fluoresce. I don't see that it makes everything look purple to the eye, which would be the case for the cheapest lights. The purple color I get comes up in the camera.

If I understand correctly, a short pass filter on the flashlight will ensure that the device puts out only short wavelength down in the UV range. But I don't at this point understand why that matters so much.
Putting a long pass filter over the camera lens is intended to block UV light from entering the camera. I did not know the terminology other than "UV filter". I have a basic UV filter but I'm sure its not considered a good one for that purpose. I did a test to see if it blocked enough UV to keep objects from fluorescing under the flashlight. It didn't.
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blekenbleu
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Re: Questions about UV fluorescent photography

Post by blekenbleu »

MarkSturtevant wrote:
Sun May 29, 2022 6:15 am
The purple color I get comes up in the camera.
Purple means that red camera sensors are being stimulated, in addition to blue.
Silicon sensors are naturally sensitive to red and have filters to compensate,
but as you note cannot fully match human color perception.
Metaphot, Optiphot 1, 66; AO 10, 120, and EPIStar 2571
https://blekenbleu.github.io/microscope

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Re: Questions about UV fluorescent photography

Post by Pau »

MarkSturtevant wrote:
Sun May 29, 2022 6:15 am

The flashlight is from a company named STIALO, and it does not have a fancy name like yours. Here it is: https://www.amazon.com/gp/product/B0796 ... UTF8&psc=1 It will be a given that it will have emission peaks other than 365nm, but it sure does make things fluoresce. I don't see that it makes everything look purple to the eye, which would be the case for the cheapest lights. The purple color I get comes up in the camera.

If I understand correctly, a short pass filter on the flashlight will ensure that the device puts out only short wavelength down in the UV range. But I don't at this point understand why that matters so much.
Putting a long pass filter over the camera lens is intended to block UV light from entering the camera. I did not know the terminology other than "UV filter". I have a basic UV filter but I'm sure its not considered a good one for that purpose. I did a test to see if it blocked enough UV to keep objects from fluorescing under the flashlight. It didn't.
- It seems that the emission peak would be around 385-395nm (although it isn't well described) This will emit lots of visible violet light, didn't it? and also it is towards the longer UV so the chance that it could hit the sensor could be important. Even good brand UV LEDs like Nichia 365nm emit a good amount of visible violet. This is why emission (short pass) filters matter
- You have it right with the long/short pass concepts
- blekenbleu could be right although I still think that the problem is with violet and UV detected by the camera sensor.
- There are inexpensive ZBW2 filters both at Amazon and eBay, I think that they are worth to try. No experience with it but this Long Pass could be adequate: https://www.ebay.com/itm/274621860268?h ... SwT5Zf4ZSg

EDIT: Changed 285-295nm for 385-395nm, a big typo! :oops:
Pau

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Re: Questions about UV fluorescent photography

Post by MarkSturtevant »

Thank you. The flashlight will create a visible purple light, but that seems comparatively faint compared to the intense fluorescent colors produced. Still, it requires long exposure to take the picture (4 seconds), and a short working distance was also required. These are challenging conditions for this kind of photography, I would guess. From the standpoint of the camera maybe recording more purple light than red light (ignoring for the moment reflected UV light), I wonder if the camera is just more sensitive to the purple than to the red.
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Lou Jost
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Re: Questions about UV fluorescent photography

Post by Lou Jost »

Hi Mark, I was out of town for a while, sorry. I use a Zeiss T* UV filter on the camera lens, to remove any stray ultraviolet light. I also use a "tighter" UV pass filter on my flashlights, so that non-UV light from the flashlight is mostly blocked. La La U is a good one, though expensive. The Schott UG1 filter also works for me. The stock UV pass filter on those flashlights is not very good. I have not seen much purple in my photos of leaves. Some leaves do naturally have a little cerulean blue fluorescence, though.

UV fluorescence is fascinating and you'll really enjoy it once you work out the kinks. Fertile fern fronds are especially colorful! So are many opilionids. Good luck!
Last edited by Lou Jost on Sun May 29, 2022 6:26 pm, edited 2 times in total.

Lou Jost
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Re: Questions about UV fluorescent photography

Post by Lou Jost »

If your flashlight is small enough, one of the narrow bandpass dichroic filters from Edmunds or other spources are extremely good. But they are prohibively expensive for large flashlights.

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Re: Questions about UV fluorescent photography

Post by MarkSturtevant »

Lou Jost wrote:
Sun May 29, 2022 3:23 pm
Hi Mark, I was out of town for a while, sorry. I use a Zeiss T* UV filter on the camera lens, to remove any stray ultraviolet light. I also use a "tighter" UV pass filter on my flashlights, so that non-UV light from the flashlight is mostly blocked. La La U is a good one, though expensive. The Schott UG1 filter also works for me. The stock UV pass filter on those flashlights is not very good. I have not seen much purple in my photos of leaves. Some leaves do naturally have a little cerulean blue fluorescence, though.
UV fluorescence is fascinating and you'll really enjoy it once you work out the kinks. Fertile fern fronds are especially colorful! So are many opilionids. Good luck!

Thank you, Lou! (and everyone else). :)
I have been gathering notes about flashlights and filters that might clean up the UV light. The pointers given here are valuable additions. Hopefully I can make something good come from them.
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Lou Jost
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Re: Questions about UV fluorescent photography

Post by Lou Jost »

Mark, glad to help. It is really important to filter the camera lens as well as the flashlight. I've tested lots of UV filters, and most aren't good enough. The Zeiss T* UV filter is the best I've found.

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Re: Questions about UV fluorescent photography

Post by physicsmajor »

MarkSturtevant wrote:
Sun May 29, 2022 6:15 am
Pau wrote:
Sun May 29, 2022 1:26 am
Putting short pass filters at the UV flashlight will improve a lot your results. Best ones are expensive but if the size matches Chinese ZWB2 are very affordable and convenient.
Emission long pass filters for the camera/eye side are also recommendable (for the eyes wear protective glasses, any eyeglasses made of polycarbonate are effective). Generic UV camera filters I have tested are of low utility, although likely there can be better ones. The old style Nikon L39 is useful but not very efficient.
Which flashlight you have? I have the Convoy S2+ Nichia 365nm with ZWB2 filters and they are inexpensive an work very well.
Thank you both.
The flashlight is from a company named STIALO, and it does not have a fancy name like yours. Here it is: https://www.amazon.com/gp/product/B0796 ... UTF8&psc=1 It will be a given that it will have emission peaks other than 365nm, but it sure does make things fluoresce. I don't see that it makes everything look purple to the eye, which would be the case for the cheapest lights. The purple color I get comes up in the camera.

If I understand correctly, a short pass filter on the flashlight will ensure that the device puts out only short wavelength down in the UV range. But I don't at this point understand why that matters so much.
Putting a long pass filter over the camera lens is intended to block UV light from entering the camera. I did not know the terminology other than "UV filter". I have a basic UV filter but I'm sure its not considered a good one for that purpose. I did a test to see if it blocked enough UV to keep objects from fluorescing under the flashlight. It didn't.
Hi Mark,

I can simplify this for you quite a bit. I work with geologists and for mineral work almost all of their longwave UV sources have in the past few years transitioned to LEDs. There are inexpensive excellent (multi-watt) longwave UV LEDs now available. However, to get good longwave UV you are going to need to upgrade your flashlight. The one you linked is a 395nm model which is insufficient. Specifically, at present you want one with the LG LEUVA33U70RL00 diode or the Nichia U365; these are both true 365nm sources.

LG datasheet https://www.irtronix.com/_files/ugd/853 ... dad1e7.pdf.
Nichia datasheet https://led-ld.nichia.co.jp/api/data/sp ... 551C-E.pdf

This is the spectrum produced by the LG diode, clipped from the first link, but they're pretty much equivalent:
LG-UV-LED.PNG
It is centered at 365nm and almost entirely sub-400nm without spurious emission peaks. It thus appears quite dim when on... until you hit something fluorescent when it glows very brightly. However, it is producing sufficient intensity that it can activate some SW exclusive sources which happen to have a metastable intermediate state (flux is sufficiently high that a second photon can hit and excite further while in metastable state). On an 18650 battery these last days. The UI a simple click-on, click-off single mode.

The common host for this LED is the generic 18650 flashlight made by Convoy. You can buy from a site specialized for this, for a bit more
https://www.fluorescents.com/products-convoy.html

Or you can a Convoy specifically advertised as 365nm off eBay, Aliexpress, or Banggood for about half that. I've done the latter and gotten genuine Nichia LEDs multiple times.

With the proper source, you will not need a filter the light at all. I would be surprised if you need to filter the lens much to protect from spurious UV; the lens elements should block UV very strongly unless you're using exotic fluorite glass. I generally do not, but Lou could be right and I may experiment with a UV filter on the camera side.

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Re: Questions about UV fluorescent photography

Post by MarkSturtevant »

Thank you! Some of that went way over my pointy little head, but I got the important bits. I am glad that I can expect significant improvement by using a purer source of UV, as that is clearly a less expensive option.
The T-class UV filters from Zeiss have amazing specs for filtering out UV light, but they are expensive. There is a 'used' one on Amazon, but the provenance of it lends considerable suspicion that it is a counterfeit. I wouldn't go near it. Apparently, counterfeit filters are very common out there.
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Re: Questions about UV fluorescent photography

Post by Pau »

My experience is mainly with microscopes* although also have used the flashlight as external excitation source and when using both excitation and emission filters results improve a lot.
Of course a good 365nm LED in principle leaks less violet than a 390nm but the amount of violet can be enough to hide fluorescence emission if it is not very strong. The red emission of plants chlorophyll quickly fades under UV or strong blue illumination and the residual red emission is pretty faint, maybe this happened with the picture posted by Mark

The graphs published by LED makers (and also by filter makers) are often too optimistic or at least easy to misinterpret when directly transposed to the real word.

* http://www.photomacrography.net/forum/v ... 25&t=32736
(Later improved with better LEDs: NICHIA NVSU233B UV 365; LG 3535 UV 380-385nm; Cree XPE2 blue 465-480nm, a complementary light shield and several filter cubes)
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Re: Questions about UV fluorescent photography

Post by Lou Jost »

Mark, yes, physicsmajor is right, it is very important to use a good 365nm flashlight. I use a modified Convoy C8 with a long tube for two lithium batteries. I have several of these flashlights, each of which has different LEDs even though the flashes are externally identical. There are major differences in the strength (and perhaps purity) of these different LEDs.
Last edited by Lou Jost on Tue May 31, 2022 2:56 pm, edited 1 time in total.

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