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UltravioletPhotography

First Effort...


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Obviously nothing to write home about but at least I managed to get through the whole sequence. It's a quick low res zerene stack on an unmodified Pentax K5, 75 frames @250 um, 8s 100iso 6000K exposures using a Nitecore CU6 from the right on the two right hand flowers and a MTU UV301 on the left. Wratten 2a, el-nikkor 50 f/2.8. Needed lots of PP to make it even remotely presentable, and boy dead pixels really seem to show up bright with this, I had to retouch a ton away.

 

My own conclusions - need to play more with colour temperature & try out some different 2e type yellow filters. maybe try filtering the torches, and I have a UV/IR cut on its way which should also help matters. Interesting that the MTU is more purple than the nitecore. But the MTU is also more powerful. Beyond that plenty of avenues for experimentation...

 

14117441004_2e8033c84f_b.jpg

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igoriginal

Wonderful shot!

 

This is UV-fluorescence, and not UV-reflected photography, right?

 

I am curious, though, why you would need a filter like Wratten 2A or equivalent ... if you are using relatively "normal" shutter speeds?

 

Wouldn't using UV-cut / suppressive glass become irrelevant, if you are shooting at faster shutters (1/10 sec or faster), because there really won't be any significant amount of UV energy being added (or photonically "built up") into the image, at faster shutters. In fact, "normal" shutter speeds effectively act just like a UV-block glass, since so very little usable UV energy exists within common light sources, as it is.

 

I have always suspected that Wratten 2A (and equivalent glass) may even suppress a small amount of violet / blue-end visible light, robbing some blue-end color from your finished exposures ... because the listed cut-off of 2A glass is 405nm (although may continue some level of suppression, however declining, into slightly higher bandwidths above the 405nm line). And that would, of course, infringe somewhat into the visible end of energy, and take away from your photo, wouldn't it?

 

At least, this is what I am assuming, anyway. Unless I am missing something in this case? Thanks.

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igoriginal

Nevermind. I missed the part about you listing your exposures as being 8 seconds long, each.

 

In that case, I now see why a UV-block might be needed in UV-fluorescence photography.

 

However, is UV-fluorescence photography not possible with a faster shutter speed, provided a more powerful and / or full-spectrum light source?

 

I ask, because I have only had experience with UV-reflected photography, thus far. But I always assumed that UV-fluorescence photography doesn't have to be constrained / limited to the typically slower shutter speeds of UV-reflected photography?

 

Thanks, again.

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Thanks for commenting!

 

It's very very early days for me and UV fluorescence so I can't say I have the answers the point you raise :)

 

I did convert a Cactus KF36 flash to full spectrum last week but it seemed to me that the uv fluorescence would be drowned out by visible light if I used that. Hence the torches.

 

The Wratten filter was there to block UV although I have quite a bit of experimentation to do to see if this is the right approach :)

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Is it one of the Scilla species?

 

I do not know about Nitecore, but MTU needs to be fitted with UV pass filter - it emits small amount of violet, which, albeit very small, in case of UV-induced visible fluorescence photography, will contribute considerable amount of information to the final image.

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I had to look it up but yes! Scilla - a common bluebell. They're all over the place in the UK at the moment.

 

Btw for your interest that nitecore torch is much weaker than the MTU but also very 'pure' - much less purple 'spill'. You can see the difference if you mess with this photo in photoshop and push the blue/yellow slider to the left, the 2 on the right had nitecore light, the one on the left MTU.

 

14098243776_4e3c7b43d3.jpg

 

In terms of UV pass, I do have the Baader Venus filter and I'll give that a shot, but I gather you use Schott UG1 on your torches for this purpose? Which thickness do you recommend? There's no way to eliminate the spill with PP because it overpowers what we're looking for, is that about right?

 

Thanks

-Johan

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Andrea B.

UV-only illumination can induce UV fluorescence, also can induce Visible fluorescence, and also can induce Infrared fluorescence - in appropriate subjects, of course. Sometimes you can get a mix of fluorescences in the subject. Therefore, without the correct blocking filter on the lens, you will not usually know what type fluor you have induced. For example, to record Visible fluorescence, you must use a Baader UV/IR Cut filter on the lens. (While not perfect, it seems to be the best we can do currently. But do experiment.)

 

For some illumination sources you also need to add a filter to the source to ensure you are lighting the subject with the desired excitation wavelength. So if the fluorescence is to be UV-induced, then make sure your illumination source is passing only UV by blocking any side Visible (or IR?) leakage from the UV torch or lamp.

 

Fluorescence photographs are made in the dark to keep the source illumination pure. (In my case, the coat closet is used !!) Set everything up, get focused, add filters, turn on your pure source, close the door and shoot away. And note the long exposures.

 

**********

 

Igor writes: Wouldn't using UV-cut / suppressive glass become irrelevant, if you are shooting at faster shutters (1/10 sec or faster), because there really won't be any significant amount of UV energy being added (or photonically "built up") into the image, at faster shutters. In fact, "normal" shutter speeds effectively act just like a UV-block glass, since so very little usable UV energy exists within common light sources, as it is.

 

Igor - UV light is not "slow". :) You cannot block UV by using a fast shutter speed !! The speed of light is the speed of light. Don't confuse that with the composition of wavelengths within the light. There may very well be a small amount of UV in an illumination source, but it will hit the sensor. Whether or not it will contaminate the photo depends on filtering, etc.

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Thanks Andrea,

 

I ordered a Baader UV/IR Cut last weekend and I'm waiting on it - and have the Venus filter already. Regarding the studio, mine is the scruffy corner of the study...

 

14121487091_10b6a352e6_b.jpg

 

 

One q though - infrared fluorescence. Is that actually visible on a photo when visible is also there? Isn't it drowned out by the visible?

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In terms of UV pass, I do have the Baader Venus filter and I'll give that a shot, but I gather you use Schott UG1 on your torches for this purpose? Which thickness do you recommend? There's no way to eliminate the spill with PP because it overpowers what we're looking for, is that about right?

 

Thanks

-Johan

 

I use UG11, 2mm thick. Any type of colour contamination indeed can not be completely removed in the post-processing.

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Now we're cooking, I think? Didn't bother with a stack but nice purdy colours. This is with just the Nichia torch and with a Baader Venus filter over the torch. Turns out that my 43-52 step up fits nicely on the head of the mte torch, so I could add some other filters to make it sit well. One question though - the colour temperature obviously makes a large difference. Is there a 'correct' colour temperature for this?

 

14122436532_40c6f449a4_c.jpg

 

Also, I'm curious - what are the white bits? Lint? Dust? It's been sitting in quite a dusty room for a couple of days, but I don't get why they're all just around the stem and not the petals?

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igoriginal

Igor - UV light is not "slow". :) You cannot block UV by using a fast shutter speed !! The speed of light is the speed of light. Don't confuse that with the composition of wavelengths within the light. There may very well be a small amount of UV in an illumination source, but it will hit the sensor. Whether or not it will contaminate the photo depends on filtering, etc.

 

I never said that "UV light is slow", Andrea. :P Where in my entire post was that ever said? I studied particle physics for 3 years (placement within an accelerated college class for pre-NASA / rocket science) and hence understand that photons travel at the same speed (without getting into quantum mechanics and exotic theories of gravitation and supergravitation, that is).

 

Thus, go back and re-read what I said:

 

If you are shooting at faster shutters (1/10 sec or faster), because there really won't be any significant amount of UV energy being added (or photonically "built up") into the image, at faster shutters. In fact, "normal" shutter speeds effectively act just like a UV-block glass, since so very little usable UV energy exists within common light sources, as it is.

 

Notice in the phrase above, I said "photonically built up." Where in my phrasing am I saying that UV energy is "slower" than other radiation?

 

On the other hand, I feel that what I said above was generally accurate (in terms of practical application). But, maybe I was a bit too ambiguous or didn't use proper wording? Nor sure. But, to elaborate a bit more on what I was trying to say:

Since UV energy already makes up such a SMALL component (3% or less) of full-spectrum sunlight as it is, then a fast-enough shutter speed would effectively act as a sort of stand-in for a "UV-block glass" on a broad-band converted camera ... because there wouldn't be a significant amount of photonic energy hitting the sensor with a faster shutter to drastically alter the image. (Not enough to build a sufficient "UV exposure" component of the entire image).

 

But, my statement in no way was intended to imply that I assumed that photons being carried along the bandwidth range of UV-A waveforms would somehow be any "slower" than photos within the waveforms of other bandwidths.

 

The bottom line is that with "normal" shutter speeds (anything faster than about 1/10, or maybe even 1/5 ... unless you have a seriously bright aperture ratio on a UV lens, like F/1.5 or brighter .... or want to ramp up your ISO to ridiculous levels), there wouldn't be enough UV through-put (per unit of time) to build any significant amount of UV-end exposure. And this just happens to be precisely why when we do VIS photos (which involve "normal" shutter speeds), as part of our UV photo comparisons, we only need an IR-blocking glass, but not a UV-blocking glass. Because faster shutter speeds (associated with VIS photos) effectively suppress enough UV energy to prevent it from becoming a significant component of the entire VIS exposure. Hence, no fouling up of the VIS image.

 

I've actually done the comparisons for myself, to prove it to myself: Whether taking a VIS exposure using a broadband camera fitted with an IR-block glass, alone .... or fitted with an IR-block and UV-block stack ... the resulting VIS image still looks the same. Because there isn't any significant level of UV throughput, with faster shutter speeds, to make the difference in the image outcome - UV-block filter or no UV-block filter.

 

(I typically take my VIS image comparisons at shutters around 1/200 to 1/400, depending on lens, aperture setting, light intensity, and other factors. I can tell you, from my own experimentation, that no UV energy of any consequence is going to foul up a VIS image at such a shutter speed. Which is why adding a UV-block glass to an existing IR-block glass would be redundant and moot.)

 

If what I initially said sounded confusing or ambiguous, then I apologize. :)

 

(Of course, how these physics properties may apply ... or may not apply ... to UV-fluorescence photography, I am unsure of, since I have only had experience with UV-reflected photography, thus far.)

 

And thus, I wish to learn how these physics may be different, with UV-fluorescence work.

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- what are the white bits? Lint? Dust? It's been sitting in quite a dusty room for a couple of days, but I don't get why they're all just around the stem and not the petals?

 

Do I see an aphid ? Perhaps the white bits are it's doing, where it fed and created a fluorescent wound on the stem or left fluorescent excretion? If the plant juices the aphids are feeding on are themselves fluorescent it could well be both. You could video the little miscreant and see if it is to blame. Could be an novel way to document aphid presence or damage.

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Summing up the requirement of a UV blocking filter for UV induced visible fluorescence:

 

When there is a large EV difference, between the required exposure parameters to capture visible fluorescence, compared to those required to capture any reflected UV, this eliminates the need for UV blocking. This only occurs for subjects exhibiting reasonably strong fluorescence.

 

This doesn't eliminate the requirement for a far red/IR blocking filter required by "most" UV sources. On the lens, this is most difficult to balance between red/IR source leakage and red porphyrin fluorescence for example, and therefore it's best to place the R/IR blocking filter over the source.

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Ok, son had hospital appointment so I took a day off work, this is hopefully the final of the testing shots for now until next month, when I can get another MTE and venus filter which should allow me to do this properly. This one was a proof of concept to add background, one that I can control - not a background in post. I use this technique in my extreme macro stuff too, except I added some white non-shiny plastic bags in front of the screen, because they are dark under UV so don't glow (obviously not bleached like paper). Also I needed to tone down ambient background brightness enough that it didn't overpower the UV fluorescence. Works nicely. Tick in box.

 

With background:

 

14106663756_879c364211_c.jpg

 

Comparison without:

 

14149906793_cff831e075_c.jpg

 

How: http://extreme-macro.co.uk/field-monitor/ and http://extreme-macro.co.uk/hdmi-matrix/

 

Still unclear about colour temp. No 'technically correct' I think?

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Colour temp doesn't apply in the normal sense. Colour temp correction compensates for the light SOURCE so that the reflected colours appear "normal" in the image. In this case, your source is the fluorescence and obviously that may include several different emission colours. In the days of film, Daylight balanced film typically worked best and for digital the same really applies, the simplest method is to use Daylight WB. You can always tweek the WB in raw PP if necessary to push the fluorescence colour towards what you perceived as the "correct" colour.
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Thanks Shane, good steer, appreciated. I did some searching and that was the answer you gave elsewhere so had decided to strive for that. Though in my case it's slightly complicated because of the mixed in ambient background... but I think I can get a result out ok. Thanks again!
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Andrea B.

One q though - infrared fluorescence. Is that actually visible on a photo when visible is also there? Isn't it drowned out by the visible?

 

The only way you are going to know at all that you have induced dual Vis & IR fluorescences, for example, is to first record using a UV/IR blocker and then to record using a UV/Vis blocker. So no drowning happens, only blocking of the unwanted wavelengths.

 

But really this is all getting far away from the topic at hand - which was, I think, learning to induce and record fluorescence in a flower by appropriate filtration of both your illumination source and your lens. :) :) :P

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Andrea B.

The "spill", BTW, is likely because your combination of pass filter (on light source) and block filter (on the lens) has some overlap in the purple/blue region.

Fluorescence studies are typically performed with very narrowband filtration to prevent this kind of thing. But it is costly to purchase and use such filters, so we muddle onward with broader band filters. "-) The results are usually pleasing anyway.

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Thanks Andrea - that's kind of what I'd figured, good that I'm vaguely on the right track. Onward with the muddling =)
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