365nm UV Flash?

[Pylon]

You would think by now, excluding the Baader-U, there would be a 300-400nm UV-only filter available, available in any size....

But you need to get 2 filters (a UV+IR filter, and an IR-blocking filter), and then stack them to get a UV-only filter.... >:[

 

Has anyone here purchased a custom filter from Omega Filters? If you were to order a Baader-U clone, how much more expensive would it be, I wonder?

[Andrea B.]

There are not that many people doing UV photography. And most do not wish to pay $350-$500 for hardcore, so to speak, UV-pass filters. So there is probably not much incentive for anyone to develop new filters, Reed's efforts notwithstanding (and which were probably the first new commercial UV-pass filters developed in quite some time?)

 

The much less expensive stacks work quite well, give or take a bit of flare, but that can be managed. And stacks separate into nice building blocks for various wavelength stacking experiments. It is also easier to find stack components larger than the typical 48-52mm sizes.

 

A fellow some years ago, back when we were all talking on the old Nikongear website, had Omega make him a UV-pass filter and as I recall he thought it nice. They are a reputable company.

 

Many of us have some Omega Bob filters, the Ebay versions which are typically seconds. I've been shopping around for a set of narrow (10nm) bandpass UV-pass filters at Omega, Asahi, Edmund and a couple of other places. I can't decide if such a filter set is necessary for my well-being in the larger scheme of things, so I have not yet forked over the 4 figures required to obtain it.

[Pylon]

I have only dabbled with taped on filters,

What were the tape-on filters? Were they glass UV-pass filters? Were the results equal to or very similar to the results produced by a 365nm Nichia LED?

[baffe]

This is the fresnel lens of a Metz 32Zxy flash after firing a really long and quick sequence with a professional DSLR.

 

http://up.picr.de/22600201qa.jpg

 

Obviously the energy leaves the unit in a very small area. That flash is not good for filtering because it causes big thermals stress to the center of the filter in front.

 

Opposite the Metz45CTxy for example has a very big "output area" and much more output but less stress (energy per area) to the filters in front.

 

An easy test is to fire the flash against a black picture in a newspaper at a short distance. If the result looks like the picture below, burning the surface and generating smoke, then the flash energy per area is really big:

 

http://up.picr.de/22600321uj.jpg

 

That will not deliver exact values but one quickly gets a feeling which flash is good or bad to the filters.

[colinbm]

Wow, I never thought it was that big Stefan, thanks for showing.

Col

[nfoto]

Stefan: Looks like the poor Wratten gel I tried in front of my SB-140 :(

[baffe]

... but wrattens do not explode like glass filters if "overstressed" in the center!

[Andrea B.]

Cool test with the newspaper !! Thanks !!

[Pylon]

This is the fresnel lens of a Metz 32Zxy flash after firing a really long and quick sequence with a professional DSLR

Are these realistic situations one would run into when using a flash for UVIVF photography of flowers though? It seems like you would only be firing a flash every few seconds at most when photographing a flower or snail. Maybe you could still use that fresnel lens if you just waited for a few seconds longer between each shot. What was the speed? Were you blasting out full powered flashes every 4 seconds for 20+ seconds or something?

 

Bjorn said that he had a wratten filter up next to the SB-140 and it caught on fire, was that filter made from a different material (one that can't withstand the thermal load) when compared to the SW-5 UV? If so, what special properties does the SW-5 UV filter have when compared to any other filter? Maybe glass can easily withstand thermal loads when compared to hard brittle plastic, or plastic film gels? Are wratten filters plastic film gels?

[Pylon]

Here is how I made the SB-140 a little easier to carry around and use.... I just wrapped everything up around the battery pack, including all the cords, neck strap, PC-sync wire that leads to the wein safe sync + wireless trigger. This seriously is far from the ideal situation though lol

[Pylon]

JCDowdy, have you done that newspaper test? I want to get the Canon 199A and put a UG11 + S8612 stack on it... so far it sounds like it is the best solution. I'd order everything right now if this thermal load thing wasn't a concern.

[baffe]

Pylon during that shooting I was firing everything the cam could fire. 10 shots per second for 5 seconds. Repetitive :-)

 

I didn't take care for that flashes. Important were only the pictures!

 

...and if a flash gives up I take the next one.

[nfoto]

It was a Wratten 87 gel and you could see the puffs of smoke coming out of it when the flash was fired the first time. Afterwards it was badly crinkled and could never be used over a lens again. Next try it caught fire. Given the intense heat wave emerging from my studio flashes when they fire, I won't try any filter right in front of them. However I believed the much weaker SB-140 would be safe.

 

The SW-5UV filter is glass (I have a broken one, plus one still intact). The IR versions and the SW-5V for visible apparear to be plastic of some kind.

[JCDowdy]

JCDowdy, have you done that newspaper test? I want to get the Canon 199A and put a UG11 + S8612 stack on it... so far it sounds like it is the best solution. I'd order everything right now if this thermal load thing wasn't a concern.

 

Yes, it just did but so would probably any other strobe w/o Fresnel lens. It is the black ink that is cooking off, no smoke from white paper.

 

I also just repeated the test where I flashed a 4mm thick KOPP 9863 as fast as the 199A could recycle ~12-15 sec on relatively good batteries. The 199A manual claims 10 sec for fresh alkaline and 6 sec on Ni-Cd until pilot light comes on. I waited until it was flashing and after 10 shots measured filter temp with a telethermometer and it was only ~115-120°F on the side facing the lamp.

 

I suspect the filter on the SB-140 will most likely not break under fire. I just scanned the manual and saw no precaution against rapid cycling or warning of thermally breaking filters. With an SB-140 you are halfway thare, stick an S8612 or BG-filter in front of it and see what you get. If I was concerned about breaking a collectible SB-140 filter I would buy a clone and bang away!

 

I settled on the 199A as a UV capable strobe primarily because it is easy to remove the Fresnel and, unlike your Classic Cadillac SB-140, very (~$10-$15) very cheap. I would not discourage you from trying a 199A if you wish, but there may be better alternatives. Perhaps other members might recommend something mote suitable to consider.

[baffe]

>Yes, it just did but so would probably any other strobe w/o Fresnel lens. It is the black ink that is cooking off, no smoke from white paper.

 

The distance it smokes gives a rough overview over the density. The newspaper solution is quite sensitive "against a black picture " like i wrote above. The flash shown in my picture has a distance of something round 20mm.

 

JCDowdy: "It is the black ink that is cooking off,..."

 

Of course and most of the ink is on the "black pictures".

 

A powerful studio flash will even burn leather and plastic at short distances!

 

And no, not every flash and not every flash with fresnel lens will produce that smoke at a small distance. Nor is the power (guide number) a reliable indicator for the density of energy in the beam.

 

For example the homemade one doesn't even burn wrattens sticked onto its glass after dozens of shots. I use them very often and I did not even notice any wear on them!

 

My Phillips flashes even have a slot to put in Filters into the small gap between flashtube and front pane and I never had any wear on the filters!

[JCDowdy]

Of course you are correct, I sad that wrong. What I was thinking was comparably powerful strobe of the type I thought we were discussing.

I did say "probably" though I should not have said "any", when one speaks in absolutes one is almost always wrong........

 

Do you think this "smoke test" indicates filters should not be used on the strobe? Bjørn's account of smoking a gel with an SB-140 which is usable with a filter perhaps not?

[baffe]

Polarizer foils are both, very sensitive to overheating and expensive. I made shots with them and noticed that some flashes destroy them very quickly and others do not at all.

 

I think you can use a filter on any flash, but if the flash you want to use with filter "smokes" at a distance of 2 inches (50mm) then I would not put an expensive filter at a closer distance to the flash.

 

Just set a simple paper roll or something like that between flash and filter equalizes the density over the area and decreases stress.

 

It depends on the filter too. If the energy is absorbed in a thin layer (i.e. polarizer, dichroitics) or inside a volumina (i.e. UG11)

 

And I forgot to tell one important thing: The energy density of flashes with zoom depends on the focal length they are set too. Perhaps not so important if one removes the fresnel.

[Pylon]

My Phillips flashes even have a slot to put in Filters into the small gap between flashtube and front pane and I never had any wear on the filters!

 

Are these Phillips flashes you speak of modded for UV? If so, was it easy/fast/safe to mod them?

[Pylon]

Also, JCDowdy, have you used your flash with a filter stack on it for UVIVF before? How were the results?

[Andrea B.]

Baffe: volumina ?? We need to figure out a translation for that.

I think you are saying the flash energy is absorbed by the entire volume of the filter and not just by a particular layer?

If not, then explain further.

 

Thanks!

[baffe]

Thank you Andrea thats wat I wanted to say.

 

The power dissipation appears to a relative small mass in case of a layer resulting in high temperature or almost the entire volume with big mass resulting in lower temperature.

 

No. I don't use the Phillips flashes for uv but for colour filtering.

[Johan]

Hello Pylon,

 

I've done what you're proposing, and can help a little, from memory. Unfortunately all this apparatus is currently in storage so I can't get at it easily for the time being to test anything else, sorry.

 

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?

 

I wasn't hugely impressed with the strength of one single modified flash and remember having to use it at 1/1 and very close to get anything out at all. Same with David Kennard. I didn't use a Vivitar 285 but a Cactus KF36 (same flash, same factory, different badge). I removed the fresnel and replaced the front with a clear uv transmitting cover out of a hard (3mm?) pvc, then made various slipon attachments that go on top to test UV pass options inc. Kopp 9863, Baader-U and Proprietary Schott-like material from a friend at Mineralogical Research Company USA.

 

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.

 

Yes. I didn't have any problems with exploding or melting etc. Gels arn't the right solution because they melt but the glass fliters I used had no problem. Obviously I didn't go crazy at 5fps (TBH the flash doesn't recharge that fast anyway), I suspect that the PVC layer blocked heat before it could reach the glass filters anyway. If I remember rightly you have to do a little research to find the right PVC-like material layer because some will block UV, I remember that being a bit of a pain and sorry can't remember what I used. But easy to test with a torch anyway.

 

In all, my thinking was very similar to yours but I ended up preferring just using torches. Though will doubtless try and make a better one sometime in the future - I'm a little suspicious that there maybe a lot of variation between early and late Vivitar and Cactus flashes so want to try this with a real, early one again sometime. Modding the flash isn't that hard, you have to twist and break things off but I didn't come anywhere near the electronics.

 

Anyhow some links here - you can see it's comparable to the torches - http://extreme-macro...hting/#uvtests1 and http://extreme-macro...hting/#uvtests2

 

In terms of what you're seeking, although I can get away with torches and excruciating high ISO, I do think that the ultimate solution is some sort of modified flash along these lines, probably several firing in unison. In truth I envy your Nikon unit because it's always been held up as the ultimate. I also tried an ancient ringflash to see if it had UV output but sadly no, and obviously they're tricky to filter. But I should imagine that somewhere out there there's bound to be a type of vintage flash unit that outputs UV and that can be covered in this way. After all there are lots of old flashes around and safety regulations were a bit less stringent back in the day. Unfortunately I havn't found it yet :(

[nfoto]

Although the SB-140 is OK for field work, as it is pretty small and portable all things considered, much better UV illumination is provided by studio flashes using uncoated xenon flash tube. Bron has a UV attachment that looks like a big bulb and it delivers UV peaking at ~365 nm, but the output is not narrowband.

 

I have a battery pack for my Broncolor flahes that delivers 220V A/C so can make a 'transportable' field studio in the rear of my car.

[Andrea B.]

But Bjørn would that Broncolor studio flash work well to induce UV fluorescence? Seems like it should, but I've never done UViVF with flash units. Yet.

[Johan]

Andrea, I don't see why not, sounds like a great solution albeit maybe a tad wanting on the portability end :D The long exposure time required for the UVIFL with torches is quite tricky for many of us insect macro types, the OP and I wouldn't be the only ones interested in solutions.