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UltravioletPhotography

365nm UV Flash?


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EDITOR's NOTE: Please read our post UV and Your Eyes :: UV Safety Reference.

You must always wear protective UV-blocking goggles when using artificial UV illumination.

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I was outside last night taking UVIVF images of snails, insects and plants with both a 365nm UV LED and the SB-140 flash with UV filter on it.

 

The 365nm UV LED doesn't have as much purple/violet as the SB-140, which I like. See comparison test below in my response post and also here..

 

However, the SB-140 is a FLASH, and because of that I like it MUCH MORE because it can freeze motion with a shutter speed at 1/250", easily rendering images sharp, especially of moving subjects. Flashes can produce more uniform/evenly-distributed light as well when compared to long exposure UV LED light painted images, which often takes 5+ seconds to capture.

 

The DOWNSIDE is that the SB-140 SW-5 UV filter isn't a narrow-band 365nm-peaked-spectrum like the Nichia UV LED torch is, the transmission chart of the SB-140 UV filter is more spread out and leaks past 400nm into the VIS range which gives out a lot of purple (which can be cool too, but usually the non-purple images appear more professional/colorful and less dorky/goofy to me). I also hate how the SB-140 is very large, oddly shaped with buttons and switches in weird locations, and has a big clunky external battery pack that takes C batteries - it is very very inefficient and difficult to use when compared to using a regular sized flash that takes 4 AA batteries with a wireless trigger on the bottom of the hotshoe foot.

 

So, I am trying to find a more efficient UV flash solution.

 

I see on the UV Sticky that you recommend a modified Vivitar 283/285/285HV flash. (the UV Flash links need to be updated on this page btw)

 

The other option listed is the "Kohlrusch Technical Light", however I can't read anything on that page and I see no images of the unit.

 

The last option is the Nikon flashes, but I'd like to get away from the Nikon units because of how large/clunky/inefficient they are when compared to something like the Vivitar 285HV. The UV filter that comes with the SB-140 also leaks a lot of IR, which is not ideal - I want to replace that filter with a REAL UV filter and then sell my whole SB-140 kit after it has been replaced with a Vivitar 285HV + UV filter + IR filter + VIS filter kit.

 

Also, there apparently is a "QFlash" + UV filter, which I don't know much about, but it looks like the reflector is kind of large, so again the 285HV might beat it in that regard, but if it is super powerful then maybe it would be worth getting that flash... I just don't know anything about it.

 

So, I have two questions:

 

1. Once the Vivitar flash is modified for full-spectrum, what does the spectrum chart look like, and how much power does it have when compared to the SB-140 or the Qflash?

 

2. Once I obtain a full-spectrum flash, what UV-only-pass filter can I put on it to make the light coming out of the flash look like the light coming out of a Nichia 365nm UV LED? (update: I've confirmed recently that the 365nm narrowband light isn't required to remove the purple, you can use a broadband UV light and it will look the same as the 365nm narrowband UV LED as long as the lightsource has a sharp VIS/IR Cut, and your lens filtered for VIS-only.

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enricosavazzi

Xenon flash tubes of the type used in electronic flash are broadband emitters. The emission spectrum covers UVA (and shorter wavelength if the tube is uncoated and made of fused silica), VIS and NIR. The proportion of NUV varies with peak current density (there was an old NASA study about this, I cannot find the reference), so it is possible to enhance the UV emission by a moderate amount (1-2 stops) by increasing the current density, usually at the expense of shortening the useful life of the tube. A very short, very UV-rich emission is possible with special drivers and capacitors, but quickly does bad things to the tube glass.

 

You can safely assume that most battery-powered electronic flash units have a fairly constant NUV/VIS emission ratio (once UV-cut filters are removed), since they use similar electronics and capacitor voltages.

 

Battery-powered units like the SB-140 and 285HV emit a fairly linear UVA+VIS+NIR continuous spectrum from 320 nm and up, not sharp emission peaks like a mercury arc. If you want to use the maximum amount of produced UVA, use a broadband UV-pass filter like the Baader U. If you use a narrow-band 365 nm filter, you will probably lose roughly 80% of the emitted NUV.

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Evan,

 

You are fortunate to have the absolute Cadillac UV-flash!

The spectral output is specified in the operators manual on pages 36-37, download bilingual version here if you don't have one.

 

You can also find instructive information posted by UVP member Shane Elen website about the transmittance of the SB-140 SW-5UV filter.

 

What these graphs show us is that the SW-5UV filtered SB-140 emits some visible blue light >400nm as well as some visible red >650nm in the secondary transmittance band of the SW-5UV filter.

 

You do not mention how you are filtering your camera lens but from your other post it seems to be an unfiltered unmodified camera. Clearly the camera remains normally responsive to the visible wavelengths emitted from the SW-5UV filtered SB-140. To image only UVIVF you would need to filter the lens to narrow the spectrum transmitted to the sensor to exclude both the blue and red light coming through the SW-5UV filter.

 

You could alternatively construct an custom filter for the SB-140 to contain whatever filter(s) you desire. Shane Elen, as noted in the link above, has cloned the SB-140 flash adapters by retrofitting the Nikon SW-5 adapter with alternate filter materials. If I were you, I would confer with Shane about sourcing an adapter.

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To image only UVIVF you would need to filter the lens to narrow the spectrum transmitted to the sensor to exclude both the blue and red light coming through the SW-5UV filter.

 

JD !!! If you block blue and red light at the lens, then you cutting 2/3 of the possible visible fluorescence leaving only green to be recorded. But there may not be any green fluor !!

 

The only feasible alternative is proper blocking on the excitation illumination.

 

But all that aside, I still don't think UV flash is the best choice for inducing fluor. Going with a Blak-Ray or some monolight or a UV-LED is the best thing for generic UVIVF.

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Andrea,

 

I completely agree, narrowing the spectrum transmitted to the camera will narrow the spectrum of fluorescence imaged. I was merely stating a technical point. Feasibility of that approach would depend on what type of fluorescence one wished to record. Narrowing the excitation source to the extent of replicating a narrowband LED also limits the fluorescence to only that excited in that narrow band.

 

I also agree it is likely preferable to filter the source. I do not know why a flash should not be a good source, a lot of the clinical fluorescence systems use them, "leaks" included. I don't have one so I don't know, it may not be worth trying. Including the contaminating VIS from the excitation source to me seems incorrect but many do. Weak fluorescence is likely more easily imaged under constant illumination with longer exposure.

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Understood....it just tickled my funny bone about hoping for green fluor. :D :rolleyes:

 

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I think my experience in UVIVF - which is not extensive (at least I don't think it is) - has been so far that the exposures made in the dark closet (sigh) were long. So therefore I was thinking flash would be too short to capture much. And also the flash is more difficult to filter than is the UV torch.

 

Also your point about weak fluorescence plays into this. As I work mostly botanically and many flowers don't fluoresce all that much, I again encounter the long exposure thing while trying to get something to show up.

 

But..............let me try some UV-flash for UVIVF and get back to everyone.

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Baader U may be to fragile for such use. I am thinking whatever works well as a lens filter stack would filter a flash just fine.

 

Stack a few mm of S8612 and UG-11 into a Nikon SW-5 adapter frame and build a better mousetrap! :rolleyes:

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How is the SB-140 the Cadillac of UV flashes? What benefit does it have over the Vivitar 285HV? As far as I can tell, the Vivitar blows the SB-140 out of the water, because it is smaller and more compact, does not have a huge external battery pack that makes using the flash a pain, and is way cheaper and readily available. The only thing that might not be good about the Vivitar is that it has less power than the SB-140, but I don't know by how much
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F5, ISO 6400, 1/160sec, temperature at 13000.... I may have lowered the flash power from 1/1 to 1/4 when I took off the Baadar-U from the flash.

post-79-0-84897100-1437276151.jpg

post-79-0-79457500-1437277820.jpg

The 365nm Nichia UV LED picture had the LED filtered with the U340 VIS-Cut filter.

 

One thing that this proves is that you don't need a 365nm narrowband light to get good UVIVF, as the 365nm picture looks the same as the pic in the top left.

 

You might as well forget about the SW-5 UV filter and just get a rectangular UV-only filter. The SW-5 UV isn't a UV filter, it is UV + IR + some VIS. On top of that, the SW 5V filter is not a VIS-only filter, it is VIS+IR. Most people won't care about this, because they are only interested in UV-only photography, or UVIVF photography, all of which can be done with a full-spectrum flash with a SW-5 UV filter on it and baader-u filter or uv/ir cut for the lens, accordingly. but what if you wanted to do an image that had UV-only light flashed in one area of the frame, IR-only light in another, and VIS in another, taken with a full-spectrum flash and a full spectrum camera? Well, having a true UV-only, IR-only, VIS-only filter for your full-spectrum flash would allow you to do that. Then if for some reason you wanted UV+IR light, you could use the silly SW-5 UV filter with an IR ND filter to slightly lower the IR output, as it is brighter than the UV itself.

 

I've also updated my original post.

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I have the Canon Speedlite 199A. Very easy to modify. No doubt safer to mod as well since you don't have to disassemble as much.

Some have claimed it is more powerful that the Vivitar 285HV, I have not tested that.

The trigger voltage on the two 199A Speedlites I have tested low enough to use safely on my Panasonics.

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Removing polycarbonate and other plastics is only one first step to the "cadillac". But there are some more steps to go!

 

My"cadillac" was a filtered 200Ws "Norman 200B", a present from a friend of mine, Dr. Schmitt. But then I modified a "Metz 45CT1" resulting in a little more "uv power" (at half the electrical input) follwed by a completely new designed, homemade unit with and uncoated tube.

 

Here on the testbench:

http://up.picr.de/22577552gd.jpg

 

The finished unit:

http://up.picr.de/22577553kg.jpg

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I did some more testing with the other flashes I have just to see what would happen, here are my results. The flower shots had the flash right up next to the flower, and the headshot was maybe 1-2 meters away, most likely on 1/1 power....

 

post-79-0-32452200-1437316335.jpg

All shots taken with CoastalOpt 60mm UV-VIS-IR lens on a full-spectrum Nikon D7000

 

Now I am wondering if I could modify this LP160 flash by simply taking the freshnel lens off of it and then scraping off any coatings on the flash tube if I have to - I wonder if doing this would make it brighter. If it did then all I would have to do is find a way to put any rectangular filters in plastic fittings that fit around the flash, then BAM: a portable full-spectrum flash with a filter kit. I forgot to test these with IR though.... but to test any flash for IR you need to put a IR-only filter in front of the flash because you could potentially be recording VIIRF (Visible Induced IR Fluorescence) and not regular reflected IR light. You also need an IR-only filter in front of the lens.

 

update: I put a 720nm IR filter in front of my lens and used the SW-5 IR filter in front of the same LP160 flash and the IR is very bright, so yes, it works. I also did it with the SB-910 and it also works:

post-79-0-42784300-1437319896.jpg

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Colin yes, there are some capacitors inside (pic of capacitor bank after finishing):http://up.picr.de/22581463jj.jpg

 

Pylon you always have a tremendous amount of ir in the light of xenon flashes! If you work inside a building then it's (in my opinion) usually not necessary to have a filter on the cam if you filter the flash.

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I called the SB-140 the Cadillac of UV flashes for two reasons: 1) It was designed and marketed for that use by Nikon to pair with the UV-Nikkor, 2) The price, like a vintage Caddy, is driven up by collectors. Designed for use with film the filters are clearly not optimal for use with digital systems with differing spectral sensitivity. It should be a simple matter to refilter an SB-140/clone for digital. Smaller, lighter, more affordable, better performance is like my KIA and fins on a KIA just seems wrong anyway.
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For the benefit of others perhaps reading this page.

 

Modding a flashlamp involves exposure to very real electrical hazard.

 

The capacitor(s) store a lot of power that can be discharged if touched incorrectly resulting in significant injury.

 

If you do not know what you are doing - please don't.

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"Significant injury" is putting it mildly.

The Darwin award has gone to more than a few who have fooled around having Unprotected Fun with capacitors.

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The voltage of the capacitor (bank) is not the only danger!

 

Discharging the capacitors causes big magnetic pulses. They "fried" my Metex multimeter and my EOS/Rebel 300D.

 

So if one has a pacemakers or implanted defibrillator he should not work on such circuits!

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I have the Canon Speedlite 199A. Very easy to modify. No doubt safer to mod as well since you don't have to disassemble as much.

Some have claimed it is more powerful that the Vivitar 285HV, I have not tested that.

The trigger voltage on the two 199A Speedlites I have tested low enough to use safely on my Panasonics.

Wireless triggers are brand-specific though, aren't they? I couldn't use a Nikon-based RF-602 or Nikon-based PocketWizard TT5 with a Canon flash... :D (I use Nikon DSLRs)

Unless... do you know of a brandless-based basic wireless trigger?

 

Also another question, do you have any UV-only filters that you use with that flash for UVIVF photography, or do you just use it bare for reflected UV photography only, w/ the Baadar-U on the lens? It looks like if you wanted to put a filter on it, you would have to unscrew it every time. Unless maybe there is another way of filtering it, with plastic fittings or velcro or something...

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A final word of defence for the poor Baader U filter: don't use it directly in front of any flash light. It is fragile and will shatter into sharply pointed shards some of which may even insert themselves into your flesh. Darwin Award opportunity here.
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Also another question, do you have any UV-only filters that you use with that flash for UVIVF photography,

 

Evan, look at places like Edmund Optics. They sell a lot of filter glass and might have something in rectangles or squares that could be rigged up with velcro, etc. You could get some kind of UG glass and stack it with an S8612 ir-blocker or something similar. You might also check with Steve at Uvroptics on Ebay. He sells different types of UV-pass glass and stacks and maybe could be on the lookout for you. There are filter glass holders for rectangular filters such as those made for Lee or Cokin filters. These filter holders are typically fitted to lenses, but perhaps could be modded for a flash? With duct tape and velcro, miracles can be accomplished!!

 

Your questions have got me wanting to rig up some kind of flash filter myself !!!!

 

If you get anything useful going, be sure to post a pic of it for us all to see!!

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Wireless triggers are brand-specific though, aren't they? I couldn't use a Nikon-based RF-602 or Nikon-based PocketWizard TT5 with a Canon flash... :D (I use Nikon DSLRs)

Unless... do you know of a brandless-based basic wireless trigger?

 

I simply don't know about Nikon wireless strobe triggers. I only have a cheap simple trigger that cannot control any settings on the strobe. It is a JTL and I do not think it is brand specific but cannot find the paperwork for it. I only use it plugged into the large RCA jack of an old White Lightening Ultra1200.

 

I use really cheap Seagull SYK-5 (essentially disposable) optical to triggers on my brace of Canon 199As, which I operate in M (manual) mode.

 

Also another question, do you have any UV-only filters that you use with that flash for UVIVF photography, or do you just use it bare for reflected UV photography only, w/ the Baadar-U on the lens? It looks like if you wanted to put a filter on it, you would have to unscrew it every time. Unless maybe there is another way of filtering it, with plastic fittings or velcro or something...

 

The 199A has a removable wide angle adapter that slips over the Fresnel as you can see below.

post-24-0-29534400-1437420489.jpg

The plastic diffuser pops out easily and measures 34.5 x 59.8 mm which is unfortunately wider than the standard 50 x 50 mm filter square. I have only dabbled with taped on filters, I am formulating my next filter stack ideas as stated earlier in this thread.

 

I see where Bjørn has added concern for fragility of the Badder-U. As a general rule when filtering an intense lamp one puts any dichroics first and then the least dense absorptive filter next in line in the beam. In a filtered xenon arc solar simulator that consists of a UV-reflecting VIS-IR passing mirror followed by a WG-320 followed by the UG-11. I am undecided which order the BG/UG filters should go to best handle thermal load in this case.

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Shouldn't there be some listing in the specs for the ability of the various filter glasses to withstand thermal load??
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It is probably not a realistic concern, given I have never head of the OEM filters on the SB-140 or Shane Elen's clone filters ever cracking from the heat of the flash.

 

I cycled my 199A as fast as it would go and could not budge a 3mm KOPP 9863. I sent a piece of it to Johan who posted results I expected from the secondary NIR lobe.

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