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UltravioletPhotography

UV transparent resin or glue?


Avalon

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So I have built UV LED lamp using 365nm 3W 14 LED's, After testing it I was somewhat disapointed since lamp produced lots of white light with some UV which didn't produce such rich fluorescence as you get with UV fluorescent tubes. I got 365nm LED specifically because painting conservators recommended this spectrum for investigation. Culprit might be that white light contaminates fluorescence of materials so I need to make for them Wood's glass or opaque UV pass filters. Although I built another UV lamp using 10 395nm and 4 365nm LED's which produced more violet light but much broader fluorescence. Problem is that since LED's separate they take up lots of space and thus I need to get large filter or make small filter for each LED's.

Since have still shards from UV bulb I came up with as idea to break up Wood's glass into fine powder and with some kind binder that passes well UV. And wolla - we have UV pass filter paint :) But challenge lies in finding resin that passes well 365nm and doesn't become less transparent to UV.

Polyethylene bag seems to have great UV transmission, since I could sense ozone when covering with it UV-C lamp. I read somewhere there is UV transparent (not UV curing) silicone encapsulant used for solar cells. Any other binder materials?

 

Here are photo's of 365nm LED lamp in operation, white light even looker slightly yellowish. Is this supposed to be so?: parduodu-3w-uv-365nm-led.jpg

 

parduodu-3w-uv-365nm-led.jpg

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Why don't you want the adhesive to be UV curing?

 

Norland has two UV transmitting adhesives that I have used, both are UV curing also. #63 and #88.

There are also UV transmitting two part epoxy adhesives that will cure with no UV, which becomes easier to use if you are mixing larger amounts.

Norland would be the way to go for smaller amounts.

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UV curing resins transparent? I assumed they need to absorb UV energy for reactions to happen. I got 5 second cure UV epoxy to try as well then. Norland 63 according spectrum chart should work great, almost up to 350nm 100% transmission! Almost looks too good to be true, did you try it?

 

Also good factors for choice to include would be resin or binder that has high or similar to glass refraction index so that filter wouldn't be frosted. Some resins after curing also become matte.

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Yeah, that seems odd. They do need to absorb to drive the reaction. Maybe the reaction products are UV-transparent though?
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UV curing resins transparent? I assumed they need to absorb UV energy for reactions to happen. I got 5 second cure UV epoxy to try as well then. Norland 63 according spectrum chart should work great, almost up to 350nm 100% transmission! Almost looks too good to be true, did you try it?

 

Also good factors for choice to include would be resin or binder that has high or similar to glass refraction index so that filter wouldn't be frosted. Some resins after curing also become matte.

 

How thick are you talking about?

The graphs for those Norland adhesives are per some thickness.

The transmission only starts to drop off at about 350nm, which is better than most UV stacks.

You need a special epoxy for UV. This one transmits below 300nm.

http://www.epotek.com/site/administrator/components/com_products/assets/files/Style_Uploads/305.pdf

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Enough to hold Wood's glass powder and give glossy coating. So that's 1-2mm, but actual resin thickness is going to be thinner due to glass filler.

By the way is it good idea to use as filter Wood's glass from incadescent UV bulbs?

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Powdered U glass from light bulbs? :) Interesting, but your on your own there...

What is that, and old hard drive case?

Your going to fill it with a mix of light bulb dust and epoxy? And that is poured into the metal case? Which will not come out, encasing all the LED's in the epoxy?

I think I would skip the epoxy, and just get a piece of 2mm thick U glass to attach to the front.

Best to use specific terms instead of 'woods glass'. Get some U-340 2mm. Don't use U-360 or UG1 for this if you want to use it for fluorescence.

If you want to use it for UV, then you don't need any filter.

I would not use the light build dust, it is not 400nm+ blocking, it transmits some visual, and blocking 400nm+ is the whole point of filtering the light at all.

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If you mix powder (=lot of little surfaces) with a resin, don't they need to have a similar refraction index to get something transparent?

Yep.

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Translucent might be the word to use here I think.

The glues/adhesives above are optically 'transparent', they will pass the light without scattering it,

however if you mix particles into the glue, then you will probably scatter the light.

Scattering the light may not be a problem here, it may work as a diffuser of sorts, however diffusing light usually cuts down on brightness.

The main question is if some of the light getting through the aggregate may actually be a mix of filtered and non filtered wavelength.

I don't think it matters if the result is transparent or translucent, what matters is

#1 if the mixture truly filters out all unwanted wavelengths

#2 if the mix cuts down on brightness

 

It would be much preferable to use actual U glass, which will not appreciably cut down on brightness, and will not transmit any out of band wavelengths.

Most "UV bulbs" transmit UV+Visible Violet and Blue, therefore the filter material used in the aggregate is not blocking 400nm+ light.

You need an actual filter glass that is specific for the cutoff you want.

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After doing some UV 365nm LED transmission test on fluorescent material I found that UV incandescent bulb Wood's filter glass had poor transmission so using it wont work for deeper UV. ZWB2 filter had much better transmission but still brightness was reduced to half when compared without filter, 400nm transmission was poorer than that of bulb glass. Good thing is that apparently 5 second UV glue has no problem transmitting 365nm. Any ideas where to get powder UV pass filter?
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I don't like the powder/glue mix idea.

Don't use ZWB2, not only because it is a cheap Chinese imitation, but also because it is a UG1/U-360 'type' U glass, you don't want to use that type, you want to use UG11/U-340 (ZWB1) type U glass for this.

What you should get is U-340 2mm glass. ZWB1 is cheap and doesn't transmit as well. I have tried it for UV-only stacks and it is not as efficient as U-340.

Some people 'think' that the 365nm peak U glass (UG1/U-360) is best to use, but it isn't, because those don't cut off under 400nm, you want U-340 2mm, it cuts off below 400nm, that is the entire point of the filter for this purpose,

limiting the transmission to under 400nm, not so much the peak, U-340 still has adequate transmission compared to U-360.

post-87-0-18847700-1540069448.jpg

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The other main problem with Zwb glass is you never know what you will get. I have a 1.8mm thick ZWB1 52mm filter and was lucky to get a good transmission one. Its 1/3 stop faster than my 2mm U340 filter. But it lets through about twice to 3 x more IR.
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I only have one sample of ZWB1, but compared to UG11 and U-340 it isn't good. I think there are many places in China making filter glass and name it whatever they want to name it, not only the Optima names like ZWB1,

but also naming them with Schott and Hoya names. There is no Schott or Hoya glass that is being sold out of China, but I have seen it listed that way.

Furthermore, there are popular well known filter sellers in the US, on eBay and other sites that are having filters made from Chinese filter glass, dirt cheap, and making quite a profit on it under their own brand names.

Very few filter makers actually say what brand of glass their filters are made from.

Another brand, Kopp, I have no direct experience with, however I have been told by a reliable source that it has a lot of imperfections in the glass, bubbles, waves, etc..

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Looks like I need to show photo proof that ZWB2 has good enough 365nm transmission - shadow is not very dark. I put together ZWB2 filter with some UV curing blue on top of it, as well I put two hot mirrors - rectangular passes better UV. I came with idea to weld with that UV curing resin PMMA lens and ZWB2 filter to eliminate additional reflection. Unfortunately EBAY PMMA lens do block a lot of 365nm. With UV curing LED, guess 395nm ZWB2 has poor transmission:

 

https://drive.google.com/open?id=18MZNo3YKqMc-2xgxdiGoiJsrTi0hkVT3

 

https://drive.google.com/open?id=1dGm9JC87eVZ-oRy9v4ND-DnZcXcb0I4l

 

https://drive.google.com/open?id=1J7uptueFhpFb1kjdV0mPu-jWLYOm81b-

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The problem is that you can’t make my sort of general statement on what “ZWB2” does or does not transmit because it’s not really one glass. You can show us what your personal filters do, but if someone else buys the filters with the same label and thickness, they might not behave the same way.
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Once again, here is how to do it.

1) Use a special glue/epoxy that is specifically designed for UV transmitting.

2) Use a UG11/U-340/ZWB1 type glass, not ZWB2, it is 360nm transmitting, but it doesn't cut below 400nm. If I were you, I would get real Hoya U-340 2mm thick, best for your money.

Stop thinking about 365nm, instead think about -400nm cut. That is the goal. And get glue that is special, made for the task. Or don't use any glue, just attach the glass on the front with air space, would that work?

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The problem is that you can’t make my sort of general statement on what “ZWB2” does or does not transmit because it’s not really one glass. You can show us what your personal filters do, but if someone else buys the filters with the same label and thickness, they might not behave the same way.

 

You mean there can be low quality ZWB2 filters with faked spectrum? Then it's another issue, defective and bad filters can be always be returned if transmission doesn't match spectrum graph.

To naked eye filter is almost completely opaque, I can see some deep red when looking into incandescent lamp and some violet only when using UV LED.

 

5 second UV glue works just fine for 365nm, it doesn't cast dark shadow as shown in photo. I plan to use ZWB2 filters mostly for 365nm LED lamp so unless they become over time opaque to UV it should do the job.

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The problem with ZWB glass is that there is not one single manufacturer. That is, there are many makers of ZWB glass. Some manufacturers have better quality control than others. Some of the ZWB glass we have seen transmits outside the stated range.
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  • 1 month later...

Are there any UV transparent resins that can be easily dissolved or melt when heated?

I could use optical cement to recement lens element but just to be safe want process to be reversible. Anyway cements also age and yellow so for UV photography it would be good idea to be able change optical cement.

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Norland acrylic clear optical cements don't yellow with age. Norland makes an excellent line of lens cements in different viscosities and with different UV transmission properties. See https://www.norlandp...m/adhchart.html

 

"The NOA bonds can be separated in chlorinated solvent such as methylene chloride." (DCM)

 

I have never had to change optical cements due to age. Removing excess Norland acrylic is easy with acetone if the glue-up has not fully cured.

 

 

Just some random thoughts.

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  • 4 weeks later...

Love to use high quality stuff but even small western filters have high costs. I need to cover at least 90x90mm window. ZWB2 might be not best quality although manufacturers still are obligated to provide tranmission spectrum promised. I bought cheapest ZWB2 and I'm satisfied with it's tranmission, tested with fluorescent background.

Another alternative would be to buy fluorescent tube type lamp and make Wood's glass powder, but why then to use LED's. Or maybe I can use nickel oxide mixed with resin to make filter?

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I think you have chasen a reasonable alternative, especially as you need a big filter glass.

 

For filtering attenuating VIS from UV-LEDs and with a limited budget I think chansing with a ZWB-type filter is acceptable, even if it is highly unlikely to be as good as a Schott filter glass

Neither UV-transmission, UV / IR transmission ratio or VIS attenuation will be that good.

 

I would have chosen ZWB1 instead of ZWB2 to get a better VIS-attenuation near 400nm.

VIS-attenuation could also be improved by getting a thicker filter glass. 3-4mm?

That will only decrease UV-transmission a bit.

 

The quality of Chinese optical filter glass in absolutely not as good as proper Schott or Hoya glass, but for illumination-filtering it can work

 

For lens-filters there is also highly likely issues with the mechanical flatness or shape from lapping and polishing in cheap Chinese filters.

That might affect the image quality, more or less depending on lens-type.

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Yes, this makes sense for the intended application. I wouldn’t use it for a lens filter but for a flashlight you don’t need perfect tolerances.
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