Constructive Critique Welcome 260nm Illumination

[colinbm]

Warning: UV-C is dangerous. Eye and skin protection is needed !

 

I am looking for Constructive Critique for this UVC 260nm Illuminated photo.
I have tested these lights with filters & a filter on the lens & the my spectrometer shows NO IR contamination with this combination, the light band is quite narrow.
The camera is a Full Spectrum with CFA intact, Sigma fp camera & a UV Nikkor 105mm lens, with a 2 second exposure time. Considering all restrictions I think this is a reasonably short exposure time. Increasing the wavelengths I am able to decrease the exposure times accordingly.
I know I am pushing the limits, but I wanted to see if it was possible, without being totally ridiculous.
I could get a de-Bayered CFA camera for pure mono images at shorter exposure times.
I just wanted to see what was there.
I have copied Lou Jost setup, for no reason but it is somewhere to start. A glass flask with water & an aluminium foil inside, a PTFE screen is behind.

 

[lukaszgryglicki]

What is the light source there and what filters? Just curious - looks great if this is at 260 nm.

 

[colinbm]

These are a couple of 260nm LED flashlights with propriety dichroic ZWB filters on the flashlights.
On the lens is an Asahi ZUSO325.
My spectroscope sees no IR with this combination.

[Stefano]

If I am not mistaken, it looks like you can see the aluminum foil inside the flask. I would not expect that at 260 nm.

 

I would test this with something which you know should transmit or block UVC. For example, ZWB2 glass or similar (Hoya U-360, Schott UG1) should be opaque there. If you illuminate a paper sheet to make it fluoresce, and put ZWB2 glass in front of the flashlight, it should cast a shadow.

 

Ordinary glass should also be opaque at 260 nm, or at least mostly opaque.

[colinbm]

I have looked at the flask & it is partly transparent to the 260mm light 
With my eye I can see the 260nm light dull on the surface of the flask & I can see the light reflect off the Aluminium inside too.

[dabateman]

Well to play devils advocate.  That looks maybe like a lab grade flask. Its possible for them to be quite pure, almost like fused silica,  but not quite.  Like jgs2 glass, especially if used for metal analysis. So its possible the camera might see the light through it.

However,  what is suspicious is that you say that you can see the light. That shouldn't be possible if it is 260nm. So maybe a leak is what you are seeing and then maybe imaging. 

 

Buy some acetone (nail polish remover) it strongly absorbs at 260 to 300nm. It should be black, and water next to it should look clear, if you have quartz cuvettes. The peak max for acetone is around 275nm. That can be a good imaging test. If you want to go deeper, use 99% isopropyl alcohol and water for controls. IPA has peak max around 205nm if I am remembering correctly.  Water has a peak max at 185nm. But thats super hard to image  

[colinbm]

Thanks Dave
I have ordered a lab grade flask beaker (quartz) & I will get some fresh acetone & IPA.

[colinbm]

@dabateman The acetone I got today blocks at 310 nm.

[dabateman]

11 hours ago, colinbm said:

@dabateman The acetone I got today blocks at 310 nm.

Interesting,  is it darker or black?

See the UV curve here:

https://webbook.nist.gov/cgi/cbook.cgi?ID=C67641&Mask=400

 

Do you have pure silver?  That will look dark at 310nm, and then reflective above and below that.

I was remembering Jonathan's images:

https://www.ultravioletphotography.com/content/index.php?/topic/4940-multispectral-imaging-of-silver-leaf-visible-and-uv/#comment-50699

 

 

[colinbm]

Thanks @dabateman
I don't have the beakers yet, but that is where the light stopped on my spectroscope .

[Andrew Dayer]

The laboratory flask you have - if it's a half decent brand - will be borosilicate 3.3 (8330) glass. The print is probably a glass - ceramic frit (not an organic ink); interesting that this is reflective in UVC. I don't know of any info on borosilicate glass being UV transmitting. It's composition is too variable to be considered a proper optical glass iirc, so only for light covers and lamp optics etc out of the lab.

 

If you can get hold of it, it might be interesting to image some ambered borosilicate glass. This is 8330 with silver ion diffusion layer on the external surfaces. Brands will be DURAN / SIMAX / BOMAX / Pyrex (lab not brown kitchenware) etc. Usually only only available as premium media bottles, sold for use with photosensitive growth media.

[dabateman]

Actually @colinbm, you should test your glass.

Place your germacidal bulb on one side, then your glass, then your held held spectrometer thing. See if the 254nm peak is still vssable through the glass.

I am seeing all types of spectra now just looking up borosilicate.  The prex borosilicate flasks I used in the distance pass, let 250nm through. The 50% transmission was around 225nm. But these may have had HCl boiled in them many times to help clean them.

[colinbm]

Thanks @dabateman
I tried to measure the flask with the spectroscope but it is difficult, insufficient light or too much scattering.
I found the beaker that I bought at the same time as the flask, no brand & cheap, it passes the 260nm LED OK.
I just put 20mm of acetone in the beaker & it starts to pass to pass at 310nm.
I don't have a continuous UC light that I can use with the beaker but I used 295, 310 & 340 LEDs

 

[colinbm]

@dabateman I have a photo of the beaker half full of acetone & photographed with 310nm LED, this is at 2 seconds exposure.
I need to keep my grubby mitts off the glass 

[Stefano]

To reduce reflections, I would try to illuminate the beaker from behind. For example, I would shine the LED onto a uniform background (even paper would work, but if you have something more reflective like PTFE it would look brighter), and I would then place the beaker in front of your background. That way you should have a cleaner image, I think.

[colinbm]

Thanks @Stefano I'll give it a try.
The background now is a PTFE sheet.

[colinbm]

I have lit the PTFE screen behind the beaker of acetone with 310nm LED flash lights.
By-the-way I have the 308nm Invisible Vision filter on the quartz lens, again 2 second exposure.

 

 

[Stefano]

That's dark for sure.

[Stefano]

By the way, what's the yellow color in your image? Is that the raw color of 310 nm light as seen by your camera? Based on collective experience, the color is often green, but not always.

[dabateman]

21 minutes ago, Stefano said:

By the way, what's the yellow color in your image? Is that the raw color of 310 nm light as seen by your camera? Based on collective experience, the color is often green, but not always.

Depends on his white balance setting.  I push my 313nm images to a golden yellow like this as well.

When Andrea looked at the raws in raw digger, it was really more of a mix with red and green.

[colinbm]

Thanks @dabateman, @Stefano
This is straight from the RAW to Tiff to JPG.
I have other shorter LED lights, 295, 275, 265, 260, 255 & the 222nm Excimer tube.
I would like to prove or disprove the 260nm photo.