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UltravioletPhotography

IR & visible light block for full spectrum flash


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Would anyone be able to give me some pointers on sources of the material that is used over a full spectrum flash to block visible and IR light?

 

There do seem to be options from Rosco but it looks as if that stuff also allows some visible light through.

 

I could take apart a woods lamp and use that, anyone tried that? Does it block too much?

 

Or, I could make a filter mount for the flash and put a baader-u Venus filter in front, anyone tried that?

 

Thank you!

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Hi Johan

You will need a 'cold mirror' to block the visible, say UG11 & the S8612 to block IR.

But just how much UV is produced by the flash & to which wavelengths is another guess......?

Col

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Yes, if you have one.

Do you know that the flash will produce UV of the required wavelengths ?

Col

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No clue, I don't have the tools to measure that sort of thing. But it shows a bulls eye when I pop it off at a yellow dandelion so it must be producing something. Only one way to find out...
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Very weak light though - even using el-nikkor 80, with the flash right next door to the flower, I have to bump the camera up to iso3200 to see a decent bulls eye. I don't know if this is normal, it's something I meant to investigate in the future. I put it down to using an unmodified Pentax K5 camera, everyone here uses full-spectrum modified cameras. Either that or the flash I modified doesn't emit as much as I'd like..
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To block visible & IR from a flash for fluorescence work a combination BG glass and UG glass can work. However, depending on the power output of the flash, and number of flashes, these glass filters can build up enough heat to crack. This can be used in conjunction with a Wratten series 2 UV block filter on the lens such as the 2A, 2E etc depending on how much "blue" you wish to pass. A more durable "lens" filter is the Baader UVIR block but this can cut-off too much red for some subjects.

 

No clue, I don't have the tools to measure that sort of thing. But it shows a bulls eye when I pop it off at a yellow dandelion so it must be producing something. Only one way to find out...

 

Remember that the bulls eye pattern on a flower can often still be differentiated right up to the edge of the UV/Blue - resulting in a weak pattern. As you mention - only one way to find out.

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... these glass filters can build up enough heat to crack.

Thanks Shane. Regarding this, I was wondering about this with regard to the Baader Venus filter. From what I understand (Which maybe wrong, please do correct me), this filter is a woods-like glass filter with dichroic coatings on either side. Have you ever heard of one being damaged by heat (as in if I make a flash filter fitting can it kill the filter if too close?)

 

Thank you

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Johan

that's kind of asking "How fast does a car go" - it depends.

 

Flash output power? time between sequential flashes? and number of sequential flashes? thermal conductance of Baader filter glass? efficiency of thermal conductance from filter mount to your custom flash mount? efficiency of heat dissapation of your custom mount?

 

The heat has to go somewhere.

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Yes, many factors involved. I've melted a fair few xpol gels in my time.

 

But in terms of Baader, have you ever actually heard of one being damaged by heat?

 

Thanks

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No - but I've also never heard of anyone using it directly in front of a flash either. I do know the multi-coatings on the Baader make it less durable with regards to cutting. This "brittleness" is probably not favorable to being placed in front of a heat source.

 

There is a catch 22 with regards to using a glass filter mounted in a metal ring and placed in front of a heat source. You need good contact between glass and metal to conduct the heat away, and you also need space to prevent thermal expansion damage. So the glass should have space around its periphery to be able to expand without damage but it needs to be in good thermal contact on its "face" where the retainer rings keep it in place.

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Thanks Shane, much appreciated! The only thing I can think of offhand is to reflect the UV with silver foil so that the silver foil carries the direct heat to a heatsink... probably a bit far fetched and I have no idea if alu foil even reflects UV!. So many questions so little time!
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igoriginal

No - but I've also never heard of anyone using it directly in front of a flash either. I do know the multi-coatings on the Baader make it less durable with regards to cutting. This "brittleness" is probably not favorable to being placed in front of a heat source.

 

There is a catch 22 with regards to using a glass filter mounted in a metal ring and placed in front of a heat source. You need good contact between glass and metal to conduct the heat away, and you also need space to prevent thermal expansion damage. So the glass should have space around its periphery to be able to expand without damage but it needs to be in good thermal contact on its "face" where the retainer rings keep it in place.

 

Speaking of techniques / methods for dissipating heat build-up ... may I suggest another idea? Designing a mountable filter unit for your flash, with a miniature cooling fan built into it, operated by a battery pack.

 

My father, once being the senior welder of the welding team at an automotive re-manufacturing plant (a retired mechanical engineer, as well), has actually prototyped welding masks with miniature cooling fans built into the entire helmet. And it still maintained its "portability", because implementing a single 9-volt battery pack (feeding power to two, 5-volt miniature computer fans embedded into the helmet) was generally non-intrusive and added negligible weight.

 

I do know that the UV-block glasses used by welders (mounted into their masks) are probably built to be more heat-resilient, but still.

 

Just a thought, as a potentially effective way to keep filter glass cooled enough to significantly reduce the risk of heat-stress related cracking. At least you're circulating some air with such a design, which is already a considerable improvement over stagnant hot air.

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Johan,

 

First, you said;

 

,,,"Very weak light though - even using el-nikkor 80, with the flash right next door to the flower, I have to bump the camera up to iso3200 to see a decent bulls eye.....",

 

so it sounds to me like your flash may not be putting out full unfiltered Xe spectrum.

 

I am sorry if you have described it previously but what sort of flash are you using and is it modified somehow, with plastic Fresnel lens removed, older uncoated flash tube??

 

I made mine from Canon Speedlite 199A, purported to "....produces more UV than the Vivitar 283/285..." ( http://www.fotozones...99a#entry356857 ) following the simple directions found here ( http://www.fotozones...for-uv/?hl=199a )

 

Second, Baader-U is a dielectrically coated Schott UG-11. As I understand the coatings are there to suppress the secondary pass band >650nm which peaks at ~715nm. I have seen UG-11 break under continuous irradiation from a Xe-arc lamp, happens pretty quick if it is in the wrong part of the beam, but some clients insist trying anyway.

 

Short flash duration and coatings notwithstanding there are of course flash guns modified with a blue/black filter for this use. They do not look like UG-11 to me, and I suspect they likely use a thin UG-5 or tempered filter similar to a MUG-6, perhaps Shane ( http://www.beyondvisible.com/ ) can enlighten us?

 

John

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Thanks gents!

 

I'm not convinced by my flash either, it's a Cactus clone of the Vivitar 285. Maybe the cactus clone isn't the old version :(.

 

Thanks for all the pointers regarding the blocking filter and cooling. Not sure if I want to risk an expensive filter but have mailed Baader, let's see what they haver to say!

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No - but I've also never heard of anyone using it directly in front of a flash either. I do know the multi-coatings on the Baader make it less durable with regards to cutting. This "brittleness" is probably not favorable to being placed in front of a heat source.

 

There is a catch 22 with regards to using a glass filter mounted in a metal ring and placed in front of a heat source. You need good contact between glass and metal to conduct the heat away, and you also need space to prevent thermal expansion damage. So the glass should have space around its periphery to be able to expand without damage but it needs to be in good thermal contact on its "face" where the retainer rings keep it in place.

 

Still wondering about this :(

 

Turns out that "Dichroic filters reflect unwanted wavelengths back to the light source. Gel filters absorb the unwanted wavelengths and dissipate them in the form of heat, ultimately leading to performance degradation (melting, bleaching out, scorching, etc.)."

 

So the polarising gels I've melted in the past actually absorbed the flash heat, so they melted. But maybe this filter doesn't take that heat in (so doesn't itself heat up I'd hope) and reflects it back at the flash. Bad for the flash, but maybe good for the filter.

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I was researching UV diffusers to diffuse the beam from the Nichia torch a bit and came across these silica diffusers. I think this maybe the answer, a sheet of this between filter and flash. Also a very useful find for my torch - the same thing from Thorlabs cost $25 but $100 to ship to the UK. Sheesh.

 

Update - changing the currency to £ rather than $ made it much better. Not too intuitive though

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I think this maybe the answer, a sheet of this between filter and flash.

 

Ii might help by diffusing the heat a bit but it will still transmit all the Vis and IR that the dark glass filter will absorb. It is all that VIS and NIR that cracks a UG-11. I am not sure if UG-11 can be tempered.

 

What diameter will you need for the torch (we call that a "flash light" on this side of the pond) I may have an alternative for you.

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If you already have filters blocking VIS and IR on your camera, then these blockers are not necessary? Unless of course you want to shoot at night with flash and no filter on the camera?

 

well, I guess if you are doing UV-induced fluorescence, then it would require this...

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igoriginal

If you already have filters blocking VIS and IR on your camera, then these blockers are not necessary? Unless of course you want to shoot at night with flash and no filter on the camera?

 

well, I guess if you are doing UV-induced fluorescence, then it would require this...

 

You cannot block VIS on the camera / lens side, if you are doing UV-induced fluorescence photography. Because VIS light is what you will be needing to record in your image.

 

You are thinking about UV-reflected photography, which is not the same thing.

 

(UV-reflected photography records UV-only light .... whereas UV-induced fluorescence photography records VIS light. UV energy in fluorescence photography is only used to induce the VISIBLE fluorescence of the object.)

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UV can induce fluorescence in any wavelength, depending on the subject, of course.

So you can have UV-induced Infrared fluorescence, for example.

 

I've written that remark just recently in another thread here.

Along with the additional remark that in scientific studies the typical practice is to use very narrow bandpass filters on the illumination source and on the lens. The generic UV fluorescence photography seen on websites tends to be rather wideband - and visible. :D

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igoriginal

UV can induce fluorescence in any wavelength, depending on the subject, of course.

So you can have UV-induced Infrared fluorescence, for example.

 

I've written that remark just recently in another thread here.

Along with the additional remark that in scientific studies the typical practice is to use very narrow bandpass filters on the illumination source and on the lens. The generic UV fluorescence photography seen on websites tends to be rather wideband - and visible. :D

 

Fascinating. It actually crossed my mind a few times (out of sheer curiosity) if fluorescence effects extended into other bandwidths besides visible. Thanks for confirming that, Andrea.

 

However, we won't really get a lot of "color diversity" out of any bandwidths, like the VIS range, right? Which is why the VIS range remains the most sought-after bandwidth for fluorescence photography, in terms of artistic appeal. Is that correct?

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