340 nm LED (first impressions)

[Stefano]

I’m using fluorescence to test the transmission of various things, and it seems that most glasses and most plastics are almost 100% transmissive at 340 nm. I have a piece of plastic that transmits really well. I didn’t expect that. I may have to go down to UVB at 310 nm to finally see some absorption. If my camera lens are made with the same glass I have around, they will transmit 340 nm.

[Cadmium]

I’m using fluorescence to test the transmission of various things, and it seems that most glasses and most plastics are almost 100% transmissive at 340 nm. I have a piece of plastic that transmits really well. I didn’t expect that. I may have to go down to UVB at 310 nm to finally see some absorption. If my camera lens are made with the same glass I have around, they will transmit 340 nm.

 

How do you know that, if your don't know if your lens transmits 340nm?

I don't think your lens transmits below 360nm, if that even.

You need a better full spectrum converted camera, and a better UV capable lens.

Invest in those first, otherwise you are wasting your time.

[Stefano]

 

 

How do you know that, if your don't know if your lens transmits 340nm?

I don't think your lens transmits below 360nm, if that even.

I don't know anything about my lens, but I am noticing that (oddly) glass seems to be transparent with this LED.

[Cadmium]

Do you know what nm you see through your glass? Glass is transparent to a range. Do you know the range of your LED? Do you have a graph?

You need a better full spectrum converted camera, and you need a lens that transmits UV down to some defined nm.

Unless you have those, you will not know, as you say, "anything".

 

You are limited by your camera and your lens. To speak about 340nm or lower without adequate equipment doesn't make sense.

[Stefano]

Do you know what nm you see through your glass? Glass is transparent to a range. Do you know the range of your LED? Do you have a graph?

You need a better full spectrum converted camera, and you need a lens that transmits UV down to some defined nm.

Unless you have those, you will not know, as you say, "anything".

 

You are limited by your camera and your lens. To speak about 340nm or lower without adequate equipment doesn't make sense.

It SEEMS that my LED is this one https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.aptechnologies.co.uk/images/Data/SETi/CUD4AF1B_R00_340_AAP63_60mW.pdf&ved=2ahUKEwiBhM-3pJfoAhVzoFwKHZ_5D3EQFjALegQIBRAB&usg=AOvVaw2PNKCuWASvPHbPWo8zXdLi You can find a graph here.

 

I'm trying to put a working link.

It should work now.

[Cadmium]

What about your tests should convince me that your lens and camera are seeing 340nm?

Your link doesn't work, by the way.

I don't believe your test are showing 340nm.

I think your equipment is limited to 360nm or above..

[Stefano]

In the midtime, go to the last link in my initial post (it should work).

[Stefano]

What about your tests should convince me that your lens and camera are seeing 340nm?

Your link doesn't work, by the way.

I don't believe your test are showing 340nm.

I think your equipment is limited to 360nm or above..

I need a way to test this. Right now I don't know what my camera is seeing. I should use something that changes between 340 and 360 nm, to be able to establish that.

[Cadmium]

Until you get a better camera and better lens, I am going to keep saying you need those. I am just being honest and real.

If you want to do this, then you need those first. LED's and filters make no sense until you have the basic equipment to work with.

You don't know "anything" about your lens, or your camera either.

 

The graph for your LED transmits up to 370nm, and that would be a best case scenario, because the range might be wider than they show.

So your tests can be seeing higher than 340nm UV.

 

[ulf]

I have a piece of plastic that transmits really well. I didn’t expect that. I may have to go down to UVB at 310 nm to finally see some absorption. If my camera lens are made with the same glass I have around, they will transmit 340 nm.

 

Optical components made of plastic are often made from some kind of polycarbonate. That plastic can be precision-injection moulded and there are much industrial experience doing so from producing optical media, CD, DVD ad BluRay-discs.

Polycarbonate is a type of plastic where the optical and mechanical properties can vary depending of intended usage.

The transmission normally begin to drop at around 390-400nm.

I think your camera's lens-elements are made of Polycarbonate.

Modern lenses have AR-coatings optimised for VIS. they normally block or limit UV rather well.

 

It is quite unlikely that your camera can see much of the 340nm light.

[Cadmium]

I don't know how you have white balanced them, but your blue/lavender/purple tests don't look like 340nm to me.

[Stefano]

I don't know how you have white balanced them, but your blue/lavender/purple tests don't look like 340nm to me.

I can't white balance when I make long exposure photos. That reddish purple should be the "real" color the sensor sees. Under WB this LED appears yellow (see my original post). I reaĺly would have expected green, the fact that I have yellow isn't very promising.

[dabateman]

The first post here has the spectra for a Convoy from someone extremely proficient at obtaining UV spectra:

https://www.ultravioletphotography.com/content/index.php/topic/2120-convoy-s2-uv-flashlight/page__view__findpost__p__15114

 

See how it has a little emission just past 400nm and alot below.

There are many other spectra here from other users.

 

I have no doubt assuming that your 340nm led has a peak similar and may even hit into 400nm that you can see.

 

I think if you can swing it get an Olympus camera and self modify it to save cost.

 

Here is how to do an EPL5 your self from the front without taking apart the camera:

https://www.mu-43.com/threads/how-to-mod-olympus-e-pxx-cameras.44060/

 

His website has more description.

[colinbm]

The first post here has the spectra for a Convoy from someone extremely proficient at obtaining UV spectra:

https://www.ultravio...dpost__p__15114

 

See how it has a little emission just past 400nm and alot below.

There are many other spectra here from other users.

 

I have no doubt assuming that your 340nm led has a peak similar and may even hit into 400nm that you can see.

 

I think if you can swing it get an Olympus camera and self modify it to save cost.

 

Here is how to do an EPL5 your self from the front without taking apart the camera:

https://www.mu-43.co...-cameras.44060/

 

His website has more description.

 

The quick & dirty.....that got it done......

[Stefano]

The first post here has the spectra for a Convoy from someone extremely proficient at obtaining UV spectra:

https://www.ultravioletphotography.com/content/index.php/topic/2120-convoy-s2-uv-flashlight/page__view__findpost__p__15114

 

See how it has a little emission just past 400nm and alot below.

There are many other spectra here from other users.

 

I have no doubt assuming that your 340nm led has a peak similar and may even hit into 400nm that you can see.

 

I think if you can swing it get an Olympus camera and self modify it to save cost.

 

Here is how to do an EPL5 your self from the front without taking apart the camera:

https://www.mu-43.com/threads/how-to-mod-olympus-e-pxx-cameras.44060/

 

His website has more description.

The LED emits past 400 nm, and even red light (like all UV LEDs, it must be filtered). It appears whitish to the (protected) naked eye. At short wavelengths, UV induced UV fluorescence can be a problem, but the graph above seems to show that my LED is not fluorescent in UV. I'm doing some tests with a USB camera with plastic lens. (without WB) 365 nm appears magenta, and the filtered 340 nm LED appears red (also with chinese BG39, so it isn't red-IR contamination). If I remove the plastic lens (I can unscrew it) my camera becomes WAY more sensitive to this light, and it still sees it as red-yellow.

[dabateman]

Red isn't too surprising. Jonathan and Andrea have commented that the red channel is actually more sensitive to low UV. Even from Rawdigger analysis of some of my raw samples.

Pushing into yellow for my WB, may have affected how I see deep UV as green.

When I got my 280bp10 filter to work on my EM1 with a crazy dangerous amount of light, it was red channel that was only sensitive.

 

[Stefano]

Here https://www.ultravioletphotography.com/content/index.php/topic/3471-coastal-optics-10545-diffraction-grating/page__hl__%2Bdiffraction+%2Bgrating__fromsearch__1 Andrea got a yellowish color in the RAW composite (that became green when white balanced).

[Stefano]

So, if my camera really sees 340 nm (it seems unlikely), should it see it as green under WB? Is 340 nm green for every sensor, like 360 nm is yellow and 390 nm blue-violet?

[Stefano]

I have looked up and N-BK7 glass transmits UV well above 350 nm, and it has still ~60 % total transmission at 310 nm (at 10 mm thickness).

 

https://www.thorlabs.com/images/TabImages/Uncoated_N-BK7_Transmission.xlsx

 

Does the link work?

[Andrea B.]

We have gotta get you access to a camera which can shoot raws, Stefano!

[dabateman]

Bk7 is not great for deep UV.

My 1.25" 63mm element ended up being Bk7 instead of fused silica. It barely transmit at 313nm. That was the limit with lots of noise. The ebay seller was great and just refunded me apologizing for the mix up.

But 350nm would be a good conservative limit.

[Stefano]

A lens made from BK7 should reach at least 350 nm, and be kind of usable maybe down to 330-320 nm. The data in my link refere to a 10 mm thick window, so imagine having 30 mm of glass. It still could work at 340 nm.

[dabateman]

I opened that and I don't believe it.

I have an uncoated 63mm single BK7 element and its horrible for UV.

350nm would be the limit for a usable image.

[Andrea B.]

a couple of comments.....

 

The human eye lens fluoresces in the blue range under UV stimulation around 320-380. (Reference needed. Cannot find it at the moment.)

The retina can detect this fluorescence. I do not recall reading how this might affect one's perception of UV light from UV-LEDs, but it must affect it in some way, yes?

 

Youth, per se, does not necessarily imply a non-yellowed lens. Although the trend over time is that the lens yellows with age, much of that depends on the life a particular person has led. If one lives in a bright sunny climate with lots of outdoor activities, then it seems reasonable to think that lens yellowing occurs more quickly than if one lives in, say, Norway.

 

 

 

So, if my camera really sees 340 nm (it seems unlikely), should it see it as green under WB? Is 340 nm green for every sensor, like 360 nm is yellow and 390 nm blue-violet?

 

We can only say what we have seen so far in examples here. And that would be that around 340nm the false colour seems to contain a green component if both the light and filtration are narrow enough. OK, that was a rather vague statement, but that's all we've got. Under a broadband filter peaking at 340 nm, false colour is, of course, more varied.

 

 

Working with JPGs is not going to give you the best experimental results because you don't how the camera is performing its demosaic and colour space assignments.

[Stefano]

I opened that and I don't believe it.

I have an uncoated 63mm single BK7 element and its horrible for UV.

350nm would be the limit for a usable image.

Maybe there are more types of different purities or something else of BK7? I believe you, but I also believe Thorlabs, I consider it a trustable company.