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UltravioletPhotography

What does the world look like at UVC?


WiSi-Testpilot

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WiSi-Testpilot

What does the world look like at 250 nm? Sunlight has weakened beneath the ozone layer. Does the sunlight still cast shadows or is it dark like on a November day or is it dark like at night?

Best regards,

Wilhelm

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It should be dark as night (or even darker). On Earth's surface, sunlight is extremely weak at that wavelength, if not undetectable. If there was UVC illumination, however, most objects would be dark. Glass would be black, people's skin would be probably dark (but nobody will do the experiment on themselves), and you would have a lot of haze. Not a nice sight.
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Andy Perrin
Yeah, I would think it would be darker than night. Not only is there no incoming light, the air absorbs over a distance of a few meters like a black fog. And most objects are black but they still specularly reflect (I think stefano was forgetting about reflections) so glass would look like obsidian. Metals probably still reflect normally at 250nm.
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The real interesting, almost unexplored, mysterious region is EUV (Extreme UltraViolet). CaF2 can bring you down to 120, maybe 110 nm, and if you want to go even deeper, you must use pinholes, remove air, and use very special light sources (do they even exist?)

 

If you want to image the world using natual light (basically sunlight), the limit is about 300 nm, and UVB is not easy to work with.

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WiSi-Testpilot

Thank you very much for your answers.

 

If you want to image the world using natual light (basically sunlight), the limit is about 300 nm, and UVB is not easy to work with.

 

Yes, that was the idea. Now I’m thinking about 300 to 320 nm.

Best regards,

Wilhelm

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Ok ran a quick test.

 

Jonathan and Andy can try to do the same test with their imagers. I added my 39mm single focal lens to my UVC imager and using the 254.3bp25 filter on the front took some images.

 

Today is clear and blue sky and rated as 9 out of 10 on the UV index. So nearly ideal.

 

I have roughly F20 aperture on the lens using about 2mm aperture on the 39mm focal length lens.

 

Now I don't know what to make of the images, as I see something.

 

U330WB80 improved filter with F20 on 39mm focal length with imager, captured with Panasonic GM5 with Olympus 30mm focused on back screen with F4, ISO 200 1/15 seconds:

post-188-0-47847200-1593020338.jpg

 

254.3bp25 filter with F20 on 39mm focal length with imager, captured with Panasonic GM5 with Olympus 30mm focused on back screen with F4, ISO 200 1/1.6 seconds (4 2/3rds slower):

post-188-0-88039800-1593020361.jpg

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I don't believe you are seeing around 250 nm, maybe if you are lucky you are down to 280 nm, but not lower (I would expect much longer exposure times).

 

Jonathan could try the Invisible Vision 308 nm bandpass filter stacked with his 4 mm thick Hoya U-340 filters (he tried this combination on his monochrome camera after I asked him if he could try it since he has both filters and it worked quite well). In that case you would see UVB, mostly if not all above 300 nm.

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Bill De Jager
Yeah, I would think it would be darker than night. Not only is there no incoming light, the air absorbs over a distance of a few meters like a black fog.

 

At 250nm UV will travel far enough through air to make germicidal lamps and arc welders hazardous at some distance without suitable protection for the skin and eyes. I head of one case where a construction worker got 'sunburn' because arc-welding radiation bounced off sheet metal stacked against the wall, traveling around a corner to where he was working.

 

On a related topic, I've been wondering about the attenuation of ionizing UV in air as the wavelength gets shorter. According to what I've read, UV is not supposed to travel through air below 200nm because it ionizes air molecules (N2? O2?). But how far would UV in that range travel (let's say to 50% attenuation) - a few cm, a few meters, a few tens of meters? I expect this would also vary by wavelength.

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Jonathan has the exact same imager and the exact same filter.

 

Andy also has the exact same imager and exact same filter.

 

Only difference is I wanted to maximize the UV, so used my single lens element. I could have tried the 60mm macro that came with the unit. But didn't think we needed consistency.

 

Hopefully Andy and Jonathan will test as well.

 

This is the transmission spectrum for my 254.3bp25 filter:

post-188-0-44298300-1593022414.jpg

 

This is the Raw spectrum for the 254.3bp25 filter:

post-188-0-14580900-1593022570.jpg

 

This is the Raw light (No filter with UV settings) for comparison used for the transmission determination:

post-188-0-12400000-1593022777.jpg

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Andy Perrin

At 250nm UV will travel far enough through air to make germicidal lamps and arc welders hazardous at some distance without suitable protection for the skin and eyes. I head of one case where a construction worker got 'sunburn' because arc-welding radiation bounced off sheet metal stacked against the wall, traveling around a corner to where he was working.

 

On a related topic, I've been wondering about the attenuation of ionizing UV in air as the wavelength gets shorter. According to what I've read, UV is not supposed to travel through air below 200nm because it ionizes air molecules (N2? O2?). But how far would UV in that range travel (let's say to 50% attenuation) - a few cm, a few meters, a few tens of meters? I expect this would also vary by wavelength.

Sure, but I'm sure if you were out in the open it would fade by the time you were tens of meters away, like in fog. I mean you can SEE in fog usually in a steamy bathroom for example. But outdoors things go white. I imagine things would go black in UVC.

 

Here is the absorption coefficient of all the major atmospheric gases:

post-94-0-00162600-1593023107.png

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No it supports your Hypothesis. You don't have enough data for a theory.

 

I think you might be correct though. I may be seeing the 290-302 edge there. I know this filter blocks IR insanly well. So I don't think its IR leakage and the center is still dark, so don't think its IR.

 

Interesting how it really makes the depth of field so thin. So most likely some low level UV.

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Andy,

your here. Please pop a 123 battery into your imager and take a shot of the back. I want to see what you get.

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No it supports your Hypothesis. You don't have enough data for a theory.

Yes, I think you are right. I can't be sure with the little information I have.
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Maybe a nice experiment would be to go in a garden, or anyway in a "piece of lawn", with a portable UVC lamp, the imager and take some images of a "wide" area. Maybe this sounds too crazy, but if you have a garden or if you can go somewhere, away from people who can look at your germicidal lamp, it could be done.
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Andy Perrin

Andy,

your here. Please pop a 123 battery into your imager and take a shot of the back. I want to see what you get.

The KSS lens won't focus far away, but anyhow, I'm sure I won't see any UVC without an artificial source. It seems more likely that in the absence of UVC, UVA is getting through the filter.

 

I don't believe you are seeing around 250 nm, maybe if you are lucky you are down to 280 nm, but not lower (I would expect much longer exposure times).

 

Jonathan could try the Invisible Vision 308 nm bandpass filter stacked with his 4 mm thick Hoya U-340 filters (he tried this combination on his monochrome camera after I asked him if he could try it since he has both filters and it worked quite well). In that case you would see UVB, mostly if not all above 300 nm.

Stefano, the device dabateman and I have is an photomultiplier tube combined with a UVC-sensitive fluorescent screen -- it is not subject to the usual limitations of our cameras, so there is no need for skepticism in this case on those grounds.

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The KSS lens won't focus far away, but anyhow, I'm sure I won't see any UVC without an artificial source.

 

 

Stefano, the device dabateman and I have is an photomultiplier tube combined with a UVC-sensitive fluorescent screen -- it is not subject to the usual limitations of our cameras, so there is no need for skepticism in this case.

I am skeptic if he used sunlight as the illumination, since there should be no UVC at ground level (or, at least, very little). If he used a UV lamp I don't have any doubt he actually saw UVC. The camera (imager) and the lens used are not limited, as you said, but sunlight has limits.
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Equally surprised and just used the sun as my source.

 

Thus I really want Andy and Jonathan to test there units out. I might also try this again on an other day with the 60mm Macro lens attached, so we can compare our geographical locations.

 

I have a handheld 250nm source light, but did not use it for this test. I should add that next time to see if it looks different.

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Andy Perrin
I currently have a 330WB80 in the 2nd filter slot (other is the transparent window) so I would have to take it apart and put the original filter back in. I guess I could do that?
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Ok, I've managed to find my Sirchie and lens (and filter), I'll get some images with it around lunchtime. We are expecting some of the strongest UV ever recorded in the UK today. I'll also try and get a sunlight spectrum.

 

And no, I haven't flocked the inside of the lens yet to fix the hotspot issue. When I got it (in winter) I put it somewhere safe until the sun came back and then promptly forgot about it.

 

When I measured the filter transmission, here - https://www.ultravioletphotography.com/content/index.php/topic/3402-60mm-f35-c-mount-uv-lenses-on-ebay/page__view__findpost__p__31367 - the long wavelength tail on the 256nm filter is obvious, and goes up well beyond 290nm. In sunlight we're not imaging at 256nm with these things. Most likely we are seeing the effect of the small amount of transmission in the 290-320nm region.

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Quick update. Had to change my plans a bit. I put the Sirchie with the quartz 60mm lens on a tripod and focused on a flower in the garden with a decent UV signature. Couldn't get any photos as I don't have a second tripod for the camera.

 

Bright (very bright sunlight) at about 10:45AM.

 

256nm filter only. Visually, through the back of the Sirchie camera I can see a faint UV signature of the flower, along with quite a lot of background haze in the image.

256nm filter plus Invisible Vision 308nm. Can still see the UV signature of the flower, background haze reduced.

256nm filter plus Baader U. Can still see the UV signature of the flower, background haze reduced.

 

With regards to the UV signature of the flower, it was brightest with just the 256nm filter. Then with the Baader U. Finally the dimmest image was when combined with the 308nm filter.

 

Based on this my conclusion is that the 256nm filter is having some small degree of UV leakage at longer wavelengths even up into the UVA, and when the device is used in sunlight with that filter it is those that are being imaged.

 

Sunlight spectra measured just after I used the camera, taken with the OO FX spectrometer and cosine corrector on the fiber. Calibrated for absolute irradiance.

 

post-148-0-13610700-1593080050.jpg

 

Below 300nm the data effectively baselines, don't forget these sort of spectrometers have some issue with stray light effects.

 

By the way, going back and looking at the transmission through the 256nm filter, it hits 1% transmission at 300nm, and 0.1% at 320nm, so I can well believe the images in sunlight are from 300+nm light.

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