Differences between normal UV and deeper UV

[Stefano]

Here I will talk about the differences between "normal", classic UV (<400 nm), and slightly deeper UV (<380-390 nm). My experience about this is the following:

-With nornal UV, you have more colors and more sensitivity.

-With deeper UV, you lose colors and sensitivity, but your images will be "more UV" than the normal UV ones (darker polycarbonate, darker sunscreen, etc.).

 

The filter I have used to cut the upper portion of UV is a 3 mm thick ZWB1.

 

For every image I used a full spectrum Panasonic DMC-F3.

 

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This is how 3 objects appear with a "light" filter (ZWB2 2 mm + chinese BG 39 2 mm).

The ZWB1 in the first image appears yellow because it blocks longer waves and passes shorter ones.

In the last image, polycarbonate appears blue for the opposite reason.

 

With the "light" filter, I have enough sensitivity to shoot in the shade, on a sunny day.

 

The 3 mm thick ZWB1 filter, with some glue on the sides because I attached it with tape.

ZWB2x2 + Chinese BG39x2

f-stop: f/2.8, ISO 1600, 1/40 s exposure.

 

Plastic lens.

ZWB2x2 + Chinese BG39x2

f-stop: f/2.8, ISO 1600, 1/50 s exposure.

 

Polycarbonate goggles.

ZWB2x2 + Chinese BG39x2

f-stop: f/2.8, ISO 1600, 1/20 s exposure.

 

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When I use the "heavy" filter (3 mm ZWB1), the goggles are completely black, even if I can still see the sun through them.

 

Polycarbonate goggles #1.

f-stop: f/2.8, ISO 1600, 1/8 s exposure.

ZWB2x2 + Chinese BG39x2

 

Polycarbonate goggles #2.

ZWB2x2 + Chinese BG39x2

f-stop: f/2.8, ISO 1600, 1/8 s exposure.

 

Polycarbonate goggles #3.

ZWB2x2 + Chinese BG39x2

f-stop: f/2.8, ISO 1600, 1/8 s exposure.

 

You can see that the goggles are slightly transparent. This doesn't occur when I use the ZWB1 (3 mm) filter.

 

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Now, unless otherwise specified, all the following images have been taken with a 10 W 365 nm LED. This LED is very powerful, it can burn paper and wood when very close. I should dedicate an entire topic to it.

 

Visible reference, taken with my phone.

Everything is transparent in visible light. The thing at the left is a piece from a broken polycarbonate goggle.

 

UV with 10W 365nm UV-LED

f-stop: f/2.8, ISO 800, 1/40 s exposure.

 

UV with 10W 365nm UV-LED

f-stop: f/2.8, ISO 200, 1/8 s exposure.

 

UV with 10W 365nm UV-LED

f-stop: f/2.8, ISO 400, 1/60 s exposure.

 

UV with 10W 365nm UV-LED

f-stop: f/2.8, ISO 800, 1/100 s exposure.

 

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Now, this is the difference a 3 mm ZWB1 makes. In the first photo, I didn't use it. In the second one, I put it over the LED to remove the upper 385-390 nm region. The difference is pretty visible. You can also notice that I lost more than 2/3 of sensitivity with the filter.

 

UV with 10W 365nm UV-LED

f-stop: f/2.8, ISO 200, 1/25 s exposure.

 

UV with 10W 365nm UV-LED + ZWB1x3

f-stop: f/2.8, ISO 200, 1/8 s exposure.

 

 

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As last images, I imaged the polycarbonate goggles and the small plastic lens with a 405 nm LED, using the usual ZWB2 (2 mm) + BG39 (2 mm) stack, and keeping the usual UV WB. Everything appears blue because UV light in that region appears blue when white-balanced. Those should be 390-400 nm images.

 

Completely transparent lens.

ZWB2x2 + Chinese BG39x2 with 405nm LED.

f-stop: f/2.8, ISO 800, 1/8 s exposure.

The spots on the paper below are burns from the UV LED I talked about earlier.

 

Semi-transparent polycarbonate goggles.

ZWB2x2 + Chinese BG39x2 with 405nm LED.

Same settings.

 

 

I have other images, but I don't want to make this post too heavy. I think that this is more than enough for now.

[Cadmium]

So are you simply switching from 2mm to 3mm thick U (ZW) glass, both stacked with the same BG 2mm thickness?

The only difference between the under 400nm and the under 380nm is the U glass is 1mm thicker for the under 380nm shots?

Am I understanding that correctly?

[dabateman]

I wonder how this thread will blow up.

We had some interesting discussion with Reed about if 400nm is the UV line.

I do see a difference between what I personally call to myself the violet upper portion of UV, being 390nm to 405nm, maybe even as high as 410nm. Then the UVA range of 350nm to 390nm, maybe just to 385nm.

Then I find 335 area different the 330 to 350nm region, so still not sure if approve of that being called UVA.

My personal opinion for UVB is 290nm to 335nm, maybe including upto 340nm.

 

The UVC is everything imagable below 290nm.

 

So I do agree there are four major bands in the UV. These are my cut offs that are not universally accepted:

UVC <290nm

UVB 290nm to 335nm

UVA 350nm to 385nm

Violet UV 390nm to 410nm

 

As these show the most difference. I would place the 335nm to 350nm hole into UVA, but not always. I'll keep it out to spark more debate.

 

The blue channel dye of our sensors is mostly sensitive to that violet UV, 385nm to 410nm. So that is what many people see as UV, also being that many lenses cut off hard at 385 to 380nm.

The red and green dyes see the less than 380nm light.

[Stefano]

For <400 nm images, I use 2 mm thick ZWB2, for <380 nm images I use 3 mm thick ZWB1, both stacked with the BG39. I can also use both stacked (ZWB1+ZWB2+BG39), although the difference isn't noticeable (the ZWB2 seen with the ZWB1+BG39 stack is almost completely transparent, with a very mild yellow hue. It can help reduce IR leaks).

[Cadmium]

Yes, when you cut off higher UV (which has the violet/blue color content) it will make things look more yellow.

Here is essentially the comparison on a graph, although I used Schott UG1, and UG11 data for this graph, and ZWB is not exactly the same, but this gives the general idea.

[Stefano]

Yes, when you cut off higher UV (which has the violet/blue color content) it will make things look more yellow.

Here is essentially the comparison on a graph, although I used Schott UG1, and UG11 data for this graph, and ZWB is not exactly the same, but this gives the general idea.

Wow, I knew that BG39 wasn't as good as S8612 at passing UV, but here the difference is quite noticeable. Only 40% peak transmission instead of 60%+.

[Andy Perrin]

40% vs. 60% is less than a stop. You have to think of transmission graphs in terms of stops because your eye and the camera both work logarithmically. But yes, there is a difference.

[Andrea B.]

Off Topic Editorial Remark

 

Member: I wonder how this thread will blow up.

 

Editor: We don't let topics blow up. We discuss, postulate, propose and investigate.

We also both learn and teach. And think. I love UVP !!!!!

 

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Stefano, I have taken the editorial liberty of adding the filter info to your photo captions. I was getting lost about what filter was used.

 

Stefano, mi piace that you make these UV experiments!

 

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[Stefano]

Off Topic Editorial Remark

 

Member: I wonder how this thread will blow up.

 

Editor: We don't let topics blow up. We discuss, postulate, propose and investigate.

We also both learn and teach. And think. I love UVP !!!!!

 

 

Stefano, I have taken the editorial liberty of adding the filter info to your photo captions. I was getting lost about what filter was used.

 

Stefano, mi piace that you make these UV experiments!

 

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I have taken the liberty to edit your edits. I didn't explain well what I did, it is a bit confusing. Now it should be clearer.

 

And, anyway, anche a me piace doing this experiments!

[Cadmium]

Wow, I knew that BG39 wasn't as good as S8612 at passing UV, but here the difference is quite noticeable. Only 40% peak transmission instead of 60%+.

 

The important part here is about the range, not so much the amplitude or exposure time, you are removing the upper range.

but yes, S8612 would improve the transmission depth. width, and peak amplitude of any u filter.

There is another graph, but my hands are full right now.

 

OK, here is an example comparing UG1 2mm + BG39 2mm vs UG1 2mm + S8612 2mm.

BG39 and S8612 both suppress red/IR the same, but BG39 cuts off more of the UV than S8612 does.

[Andy Perrin]

Now, unless otherwise specified, all the following images have been taken with a 10 W 365 nm LED. This LED is very powerful, it can burn paper and wood when very close. I should dedicate an entire topic to it.

Whoa. What are you using for eye protection??

 

Yeah, that sounds interesting as a topic, but please assure us you're being safe!

[Stefano]

Here the difference should be quite clear. Both images are frames taken from videos that I made months apart. I don't know if I used the same pair of goggles (I have three pairs), but it doesn't matter. Notice how I struggled to make a correctly exposed video with the ZWB1 (3 mm). This filter really reduces the sensitivity of my camera by a lot.

 

"light" filter (ZWB2 (2 mm) + Chinese BG39 (2 mm)). Rear side of the goggles. The sky was yellow because it was overexposed. It normally looks white.

 

"heavy" filter (ZWB1 (3 mm) + Chinese BG39 (2 mm)). Front side of the goggles. ISO and exposure were on max. I can barely record a video with this filter.

 

What do you like more?

[Stefano]

Whoa. What are you using for eye protection??

 

Yeah, that sounds interesting as a topic, but please assure us you're being safe!

I use the same goggles you see in my images. Yes, that LED is a monster.

[Andrea B.]

I needed to review the ZBW glass.

I'm using this reference chart from Optima: https://www.ultravioletphotography.com/content/index.php/topic/1313-filter-transmission-charts/page__view__findpost__p__13766

 

Roughly speaking the following equivalencies hold. (Other equivalencies can be looked up. I am referencing Hoya & Schott because we seem to use those filters a lot here on UVP.)

 

ZBW1 ~ UG11 ~ UG-340

 

ZBW2 ~ UG1 ~ UG-360

 

ZBW3 ~ UG5 ~ UG-330

 

Visible light passage or leak is discussed in these bullet points. It is only relevant if you are stacking your own filters. When these glassees are used as substrates for professional coated/dichroic filters, the leaks are stopped.

• ZBW3, UG5, UG-330 in any thickness all pass some violet, some blue and some green visible light (and additionally, they pass IR unless IR-blocked) when stacked with any kind of blue-green glass. We usually use these filters to make "insect vision" images of UV+Blue+Green. IMHO, this glass should not be used for UV only photos, but it's good for alternate vision experiments.
  

• In thickness of 1mm, ZBW1 and Hoya U-340 leak/pass a tiny bit of green around 550 nm. I'm not sure of how increasing thickness plays out here to prevent this tiny green leak. But it is something which we should be aware of. We warn against the 1mm thickness. I have some U-340 x 2mm and U-340 x 4mm which I can test for green leak (again) if anyone is interested?
  

• ZWB2, UG1 and UG-360 pass a small amount of violet. As many of you have read before, I have no particular objection myself to a small amount of violet light leak as it seems to be recorded just like high UV by our converted cameras. You just want to be sure that your ZWB2, UG1 and UG-360 are thick enough to prevent too much violet passage.
  

 

 

So, in Stefano's experiments above with ZWB1 and ZWB3, the question is this: does any kind of visible light leak play a role in the results?

That is not meant to be a challenge, it is merely a question.

[Andrea B.]

I have taken the liberty to edit your edits. I didn't explain well what I did, it is a bit confusing. Now it should be clearer.

 

Thanks, Stefano!

We want topics on UVP to serve as good references.

[Andy Perrin]

I use the same goggles you see in my images. Yes, that LED is a monster.

Yeah, get yourself a better pair. Uvex has good ones. It's been shown that even the 405nm light causes cataracts (specifically to dentists, who use the 405nm LEDs). If you can see through those with the camera, they are inadequate. Cadmium and JCDowdy did tests some time back:

https://www.ultravio...h__1#entry19704

Conclusion was to get the Amber ones, not the Orange.

[Stefano]

So, in Stefano's experiments above with ZWB1 and ZWB3, the question is this: does any kind of visible light leak play a role in the results?

That is not meant to be a challenge, it is merely a question.

As far as I know, the filters I use don't leak any visible light. I once tried, and re-tried now looking at a 10 W cyan ~500 nm LED trough the ZWB2 filter, and I saw violet light coming from the chips. I was seeing the little violet light they produced, which means that the filter worked very well.

[Andrea B.]

Update: The second Optima chart indicates an approximate 1.1% visible light leak from 400-700 nm for a 2mm thickness of ZBW2.

Geez, Optima, make that filter better!

https://www.ultravioletphotography.com/content/index.php/topic/1313-filter-transmission-charts/page__view__findpost__p__17212

 

So, same question. Does this small visible light leak play any role in making a UV-only photo using a DIY filter stack of ZB2x2 (plus an appropriate IR-blocker)?

[Stefano]

In thickness of 1mm, ZBW1 and Hoya U-340 leak/pass a tiny bit of green around 550 nm. I'm not sure of how increasing thickness plays out here to prevent this tiny green leak.

Well, it is actually pretty simple. OD is directly proportional to the thickness of the filter. If you have a 1% leak at 1 mm thickness (OD 2), you will have only 0.01% leakage at 2 mm (OD 4). So, at 2 mm or more, you should be fine.

[Andrea B.]

The experiment would be to stack the ZBW2 with a 400 or 405nm long pass filter and see how long it takes to produce a visible photo or if a visible photo is even possible.

[Andrea B.]

Well, it is actually pretty simple. OD is directly proportional to the thickness of the filter. If you have a 1% leak at 1 mm thickness (OD 2), you will have only 0.01% leakage at 2 mm (OD 4).

 

Yep. But, look at that ZBW2 x 2mm chart. Here's the link again. Scroll to the 2nd chart. https://www.ultravio...dpost__p__17212

[Stefano]

That leakage is very strange. Constant over a broad range of wavelengths, and even present in the IR region. Maybe it is an error from the spectrometer? Because I can't imagine a leakage so flat and consistent. Very odd.

[Andrea B.]

I do agree!

We simply need to stay aware of the possibility and test for such leaks. j

 

I think that I am not entirely sure whether such a 1% leak across all visible would affect a UV-only photo. Could we test that by layering together in Photoshop a 99% UV photo with a 1% layer of the equivalent visible photo?

[Stefano]

I do agree!

We simply need to stay aware of the possibility and test for such leaks. j

 

I think that I am not entirely sure whether such a 1% leak across all visible would affect a UV-only photo. Could we test that by layering together in Photoshop a 99% UV photo with a 1% layer of the equivalent visible photo?

1% of visible light may not spoil a UV photo, but if you consider that even a OD 3 UV pass filter has IR contamination, I think that you would definitely see contamination with a OD 2 filter. If you want to replicate this leakage in Photoshop, you have to take into consideration the relative sensitivities of the camera in UV and VIS. Using two correctly exposed images, even if the VIS one is reduced to 1% wouldn't reproduce the (theoretical) filter above.

[Cadmium]

Of course, OD is a product of both the U and BG combined, but it varies how much each is blocking at different parts of the range. So it is a little more complicated than making the statement about one glass alone.

As far as the 550nm leak of U-340, for example, it might leak 550nm at 1mm thick, but not at 2mm thick.

That 550nm leak can't be attenuated by the BG glass (S8612 is BG type glass too, just a reminder), not like the 700nm range leak can be.

UG11 (the equivalent of U-340) has better OD (than U-340) at 550nm, at the same thickness, but either will work fine at 2mm.