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Shortpass filter for UV Flash?
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PostPosted: Sun Jan 29, 2012 11:43 pm    Post subject: Shortpass filter for UV Flash? Reply with quote
Hello,
I like to experiment with fluorescence photography.
A have a lot ~380nm and 254nm blacklight/uv lamps, but I'm not very happy with them. They are simply not strong enough for photgraphing moving objects or without a tripod.

Is it possible to modifiy a flash with a shortpass filter to get an UV-Flash (250-400nm)?
I guess yes, but how to get a cheap shortpass filter?

I know that there are filters available from Hoya, Schott, B+W,... but they are very very expensive because they are made for taking photos directly through them.
As I need only a filter for the flash I don't care much about optical quality/diffusion etc.

Do you have any idea how to make or how to get such filter without paying a some hundret euros?

Last edited by ForenSeil on Wed Feb 08, 2012 3:22 pm; edited 1 time in total


PostPosted: Mon Feb 06, 2012 5:02 pm    Post subject: Reply with quote
Some years ago I read an article about UV-Flash. Normal Flashes produce plenty energy in all spectrums, including the UV spectrum. That´s why the glas of the flash tubes is usually thick coated to block UV. The Author rubbed the coating from the tube to enhance the UV-throughput a lot. Maybe the same is true for near IR spectrum with flashes. It was an old Nikon flash I think. So you can enhance the proportion between visible and UV spectrum so you neet to block less visible light with a filter.

For the next step, blocking the visible light, I don´t know a cheap way. For IR-spectrum, it is easy. Developed, black film sheet is almost invisible in IR and almost black in visible RL. I think, UV is more complicated. Maybe there is a cheap material invisible in UV. Did you check http://www.naturfotograf.com/index2.html or aks the author and check the LEE Filter transmission curves? Maybe a stack of more than one filter acts like a UV-only-filter.


PostPosted: Mon Feb 06, 2012 9:51 pm    Post subject: Reply with quote
UV induced visible fluorescence using a Xenon flash is a nearly impossible thing to do, so I don't recommend that. a) the energy is not enough as teh down conversion based on Stoke's Law is a very inefficient process. b) to block really all visible content of that flash is a nearly impossible thing to do. c) it can't be done cheaply.

Instead I work with high power Nichia 365nm UV LED's which nearly emit monochrome light (not really, even there is still too much visible blue light that needs to be blocked out). The exposure times are high, but the results are very good.



For moving objects that is a challenge - but are you trying to capture visible fluorescence of animals or insects? Using high power UV sources?? For me this is ethically not acceptable to harm an animal or insect.


PostPosted: Tue Feb 07, 2012 2:00 am    Post subject: Reply with quote
Thanks for the Infos.
I will have a look for these UV LEDs and I will have a look on the flash if it might be possible to get rid of any UV blocking materials.
Are these LEDs strong? Because I have a small ~5W 254nm discharging tube, which is OK for macro work, but not for something bigger than 30x30cm.

But anyway in the meanwhile I had a great idea Idea

I've slaughtered a very cheap and extremly ineffective blacklight/uv light bulp from a nearby hardware store (Google "Omnilux Schwarzlichtlampe / UV-Lampe 75W E27") and used it's glass as an UV pass filter.
(Very nice price compared to good Schott filter which would cost around 800€ for 10x10cm Wink)

I've chrushed the glas and made a filter from the shivers with a little tesafilm. After that I've taped it on an old (but fairly strong) unmodified Minolta Flash with black tape and used it with an adapter on my camera.

I guess melting the glass would produce a much better filter without any light leaks etc., but currently I don't have an a mold which could resist the heat while making a even surface Sad Any ideas?

Some minutes ago I made the very first test shots with it.


ISO was 1600 and aperture F3.5 so this flash is not very strong yet.
But it still looks promsing for a very first test. I think it will improve a lot when I will modify the flash a little (removing the plastic diffuser from the front etc.) and maybe using some more flashes (the filters are dirt cheap Smile)

Any ideas how to convert or filter the bluish areas into black without changing the colors massively, to get a picture which is complety dark except the fluourscence?
@kds - do you know any organisms which can be seen without microscope and might emit flourscent light when exposed to this flash (and are not GFP modified or colored with a dye Wink)?


PostPosted: Tue Feb 07, 2012 7:57 am    Post subject: Reply with quote
You have massive blue leak and most likely quite a bit IR also (which makes the image reddish) - that filter glass they use on these lamps unfortunately do that.

Targets? A dead scorpio would do I guess. The emit fluorescence light a lot.


(c) bugguide.net


PostPosted: Tue Feb 07, 2012 10:46 pm    Post subject: Reply with quote
The glas of these bulbs has a very unbalanced... partially it looks blue (the thinner parts) and partially nearly like black.
I think a thicker filter of this glas would lower the blue light leak.

Maybe I will buy some blow torches and melt the glass with some lead to the perfect thickness (My idea is that the liquid glass should swim on the liquid lead and produce a nearly perfect surface when cooling down slowly). But I don't know what kind of container could be used which is able to resist ~600-800°C and liquid lead without the danger of bursting.


PostPosted: Tue Feb 07, 2012 10:55 pm    Post subject: Reply with quote
A platinum one works best actually ::biggrin::


PostPosted: Tue Feb 07, 2012 11:09 pm    Post subject: Reply with quote
kds315* wrote:
A platinum one works best actually ::biggrin::


Heh, yes, reminds me of this passage from an EBC Fujinon brochure:

Quote:
Glass manufacturers used to use clay crucibles for the melting of their raw materials; at the high temperatures used reactions took place between the clay of the crucible and the molten glass it contained. This resulted in impurities. But our standards are so high that even the slightest impurity is taboo. So we have equipped our Odawara factory with platinum crucibles hundreds of times more expensive than clay crucibles.


(As it happens, this also gives a clue for the cheaper material…)


PostPosted: Tue Feb 07, 2012 11:50 pm    Post subject: Reply with quote
kds315* wrote:
A platinum one works best actually ::biggrin::

Very Happy Very Happy Very Happy
I'm not sure but doesn't the liquid lead dissolve the platinum? Wink Wink
I've also thought about metalic cooking jars and came to that problem.

I thought more about something cheap like an small (~5cm diamter) enamel pot. But where to get these?

Bye the way I don't trust clay crucibles for melting metals (even the very expensive and "clean" professional ones for chemistry labs which are made for these extreme temperatures even above 1000°C and gravimetric analysis, I have some of them).
In my own experience sometimes they burst or crack without a warning, even when cooling or heating them very slowly (once I had one that cracked while cooling it down over night in an automatic controlled high temperature oven, without any visible reason).
And liquid lead is nothing I like to have splashing around (causes serious an very painful injuries, very dangerous compared to liquid glas)

Last edited by ForenSeil on Wed Feb 08, 2012 12:57 am; edited 3 times in total


PostPosted: Wed Feb 08, 2012 12:16 am    Post subject: Reply with quote
I don't pretend to know anything about the subject, but why would the lead be a necessary component?


PostPosted: Wed Feb 08, 2012 12:37 am    Post subject: Reply with quote
Arkku wrote:
I don't pretend to know anything about the subject, but why would the lead be a necessary component?


I also don't have any real clue about producing and working with glas bye the way.
I'm only experienced with a lot of (chemistry) laboratory techniques (and how to do them at home Wink).

I think simple pooring molten glas into a mold will lead to a very uneven and thick piece of glas with my equipment.
And very hard to get usual glas viscous enough to pour it like water, it's more like cold honey at the temperature you can reach with a blow torch.

Explanation of my idea with the lead:
Some lead and some glas a placed in a pot or a bowl which can resist the stress and then it's slowly heated to ~600°C or more with some blow torches...

Lead melts already around 300°C giving a nice clean surface (due high surface tension, nearly like mercury) while the glas will begin to liquify slowly around 450-600°C.
Glas is much lighter than lead an not miscible with it, so it should begin to swim and pond (like oil on water) on the surface of the lead.

When cooling down the whole pot to ~350°C the glas disk on the surface should get hard enough to get removed with a very even thickness and glossy surface while the liquid lead remains in the pot.

So far at least my theory Wink


PostPosted: Wed Feb 08, 2012 9:03 am    Post subject: Reply with quote
Hmm, sounds perhaps a bit unnecessarily complicated to me (I would probably just first try with an imperfect approach without the lead), but… I like unnecessarily complicated. Do document it if you give this a try. =)

By the way, are you not concerned that extreme heating will destroy the filtering properties of the glass? (Again, I do not really know about the subject, so I don't know how they achieve this property in glass.)


PostPosted: Wed Feb 08, 2012 9:39 am    Post subject: Reply with quote
ForenSeil wrote:

I think simple pooring molten glas into a mold will lead to a very uneven and thick piece of glas with my equipment.


Well, unevenness and strength are mostly irrelevant - just about every parameter is secondary to homogeneity. Modern optical glass production is a lot more complicated than pouring anything anywhere...

In any case, lead is only used in form of lead salts, to produce lead glass - the metal evaporates at much too low temperature and is very poisonous. You are right in some ways regarding the use of liquid metal - nowadays, window glass is indeed cast onto a bed of molten tin, as glass will float on it (hence float glass), creating a very perfect surface in a continuous process. But that is another product, optical glass is not made in a float process.


PostPosted: Wed Feb 08, 2012 2:59 pm    Post subject: Reply with quote
Arkku wrote:

By the way, are you not concerned that extreme heating will destroy the filtering properties of the glass? (Again, I do not really know about the subject, so I don't know how they achieve this property in glass.)

Yes that might be problem. I also don't know which "dyes" they are using. I keep that in mind.

Sevo wrote:
ForenSeil wrote:

I think simple pooring molten glas into a mold will lead to a very uneven and thick piece of glas with my equipment.


Well, unevenness and strength are mostly irrelevant - just about every parameter is secondary to homogeneity. Modern optical glass production is a lot more complicated than pouring anything anywhere...

In any case, lead is only used in form of lead salts, to produce lead glass - the metal evaporates at much too low temperature and is very poisonous. You are right in some ways regarding the use of liquid metal - nowadays, window glass is indeed cast onto a bed of molten tin, as glass will float on it (hence float glass), creating a very perfect surface in a continuous process. But that is another product, optical glass is not made in a float process.


Of course optical glass production more the pouring anything anywhere, but I don't need good optical glass, a need a simple filter for a flash.
Thanks for info about the windows glass. Zin is indeed a better idea than lead because it has a lower melting point.
Zin would be als no problem to aquire for me Smile


PostPosted: Sat Mar 10, 2012 12:25 am    Post subject: Reply with quote
Update.
The project is currently on ice as I sold my DSLR and my NEX is not working with my external flashes.

But that might be interesting for followers: I just found a very easy method to reach a enough temperature to melt glass without any bunsen burners etc.
You simply have to put your crucible with your glass etc. into a bath of active charcoal (graphite powder, should be easily avaible from any hardware store as lubricant)
Gaphite absorbs all the radiation and transforms it to heat. Temperatures above 1200°C are no problem
Here's a video I made today:
http://youtu.be/K9jjboVZH7w
Flickr:
http://www.flickr.com/photos/54671350@N02/6968182259/in/photostream



Doing this with flower pots instead of crucibles at a little larger scale should also work fine (at least if the upper ones don't have any holes Twisted Evil )
Be careful bye the way Wink moltens metals at these temperature are not funny when they splash around.

I used this method while I was recycling silver from some used fixer bath etc.
Here's the result:

(The silver is only a little dirty because the crucible was a dirty)
It took 7 minutes @ 750W to melt this easily.
Silver has a melting point of about 962°C so the ~500°C to melt the glass sould be reached very fast.
(when I've collected enough silver I will make a "photo"-ring or something similar Very Happy)

Last edited by ForenSeil on Sat Mar 10, 2012 2:22 am; edited 6 times in total


PostPosted: Sat Mar 10, 2012 1:15 am    Post subject: Reply with quote
Amazing, when I thought I knew pretty much everything about photography... Shocked


PostPosted: Sat Mar 10, 2012 1:21 am    Post subject: Reply with quote
Glass such as used with pattern for leaded glass windows was simply poured out on a sheet of steel with the reverse pattern embossed in it. Perhaps simply melting the glass and pouring it on a cookie sheet would work? Then simply cut the glass to size.


PostPosted: Sat Mar 10, 2012 2:34 am    Post subject: Reply with quote
greg wrote:
Glass such as used with pattern for leaded glass windows was simply poured out on a sheet of steel with the reverse pattern embossed in it. Perhaps simply melting the glass and pouring it on a cookie sheet would work? Then simply cut the glass to size.

I think it will only work with very good preheated steel sheets as the glas would cool down faster then it floats over the surface at this scale, producing a very uneven glas plate which should also contain a lot some strains.

I think to puor it on liquid tin (or lead) (or to melt the glass directly together with them) will produce much better results.
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