The Invisible Light That Plants Emit

[Øivind Tøien]

Looks like I overestimated how dark it needs to be. A dark rainy night yesterday, and a test to see if it is possible to induce vis. light induced florescence with a hand triggered SB600 gave completely black frames at 15 sec exposure at 1600 ISO  and f/4 in my kitchen with curtains drawn. So I am abandoning the changing bag idea for now although reports from anyone who used it for this purpose, for instance in the field, would still be welcome.

[Bjørn Rørslett]

Changing bags == sure-fire method for getting dust everywhere you really didn't want it to be

Bad in the good old days for loading sheet film  into holders, even worse if you contemplate fluorescence photography. There will be bright fluorescent lint everywhere in the photo.

[David H. Hartman]

I never owned a changing bag. Is that OK?

[Øivind Tøien]

Changing bags == sure-fire method for getting dust everywhere you really didn't want it to be

Bad in the good old days for loading sheet film  into holders, even worse if you contemplate fluorescence photography. There will be bright fluorescent lint everywhere in the photo.

Thanks, another reason to abandon that idea then.

[Øivind Tøien]

The UV-light arrived quite quickly.  So I set out with safety glasses and gloves for some first experiments although the UV high pass filter has not arrived yet so there is also a reflected visible light component in the blue-violet range in these. Petals are blue in visible light on both of these flowers.

#1


D7100 unmodified, f/8 @ 55 mm, 4s, ISO 100, very heavy crop. Nikon L-39 filter on lens.

#2


D7100 unmodified, f/8 @ 55 mm, 10s, ISO 100, some crop, Nikon L-39 filter on lens.

[golunvolo]

This is beautiful work!

[Akira]

Yes, these look beautiful as they are.  I'm looking forward to seeing the results with the VIS-cut filter.

[Øivind Tøien]

Thanks for the kind comments both of you and thanks again for the help Akira. It is very inspiring to explore this new world. (It is a little bit like getting an underwater world on the surface.) I am looking forward to when the filter arrives.

[Øivind Tøien]

The  ZWB1 filter for my Tank 007 TK-566 UV torch arrived. Interestingly the before - after shots I took of a dragonfly were very similar, more variation from hand holding the flashlight. The UV flashlight already came with some kind of filter glass, although some weak blue-violet was visible when viewed from the front side as I recall. The ZWB1 filter was a perfect fit to be just attached with electrical tape to the front (might look for a more stable solution later), and looks dark to the eye except for fluorescent dust specs. With the filter attached, ball bearings look black, perhaps with only a tiny barely visible speck, and the same when photographed in IR, so generally a black frame. Only when the UV flashlight was held at a less than 5cm distance did a clearer highlight spec of the ball bearings show up in IR. Thus it looks like it is not necessary to spend $300 on a Baader-U for this purpose.

First some more captured from before the filter arrived with D7100, L-39 filter on the lens, 55mm f/3.5 AI micro as I recall on PN-11, @ f/8 nominal, exposure typically 4-8 seconds.

Visual light:
#1



UVIVF all the following, some contamination from nearby fluorescent objects likely in this one:
#2



#3



#4



#5



#6



#7



Horsetails
#8

[Øivind Tøien]

Then some with the ZBW1 filter attached to the front of the UV-LED light, all the first ones with 105mm f/4 AIS micro @ nominal f/8 mostly with PN-11 on unmodified D7100, 10-20 sec exposures.

Underside of a fern showing spore clusters (sori), UVIVF
#1



This one looks it is related to the Viola tricolor I am used to from Scandinavia, but bigger and cultivated,
Visual
#2



UVIVF:
#3



UVIVF side view reveals some "aliens" hiding inside the plant, one is about to emerge
#4



In UV-induced infrared flourescence (UVIIF) the cyan bright spots are not visible any longer:
#5



This one also appeared to be cultivated, visible light:
#6



UVIVF
#7



On the second day I had not planned anything and only brought the AW1 with me. The 11-27.5mm zoom is superb at the close limit and 27.5mm and f/6.3. The AW1 was just bracked on the desk as I do no have a tripod plate for it. These were actually better than the ones I did with the f/3.5 and f/2.8 versions of the 55mm Micro Nikkors, partly due to the resulting better depth of field. No L-37 filter used on the lens for these ones. The flower that was snatched from one of the flower beds at the university was white in visible light:
#8



UVIVF
#9



UVIF, There was a certain alien  look to it (or perhaps belonging in a Harry Potter movie look)  from the side. (anyone knows what it is?)
#10



[Perhaps this should have been a theme rather than in the gear talk?]

[Akira]

Øivind, these are interesting images.

It should be safe to assume that the bright blue color indicates the UVIVF.  On the other hand, the red petals might be the prove of some sort of visible light leak from the torch.  Then the red leaves might show the UVIIRF (UV induced infrared fluorescence) of the chlorophyll?

https://en.wikipedia.org/wiki/Chlorophyll_fluorescence

But my last assumption may well be wrong, as I've heard that it is very tricky to capture the UVIIRF.

The protection filter on the front of my TK-566 is completely clear.  I don't think it has any flitering effect on any specific wavelength.

[Øivind Tøien]

Thanks for your comments, Akira.

Interesting that your version of the Tank 007 LED light had clear glass in the front, in mine it definitely looks dark when not turned on and without the ZWB1 filter attached. This explains why my first attempts without the ZWB1 filter where not that different to the filtered ones. My supplier was ebay seller hkequipment. 

The ball bearing test rendered bearings in ZWB1 filtered UV light black to the eye (only filtered by clear UV protection glasses) and also with my D40x IR-720nm  body - hardly any specs visible at the distance used for the images. So it is safe to assume that the Tank 007 LED torch with the ZBW1 filter attached does not emit any significant amount in the visible light- or as shown here the IR spectrum (room light source left, filtered UV torch right - 20sec at ISO 100):



Chlorophyll has a fluorescence that peaks in the red part of the spectrum and extends into the IR part. However since my D7100 is unmodified with its UVIR cut filter on the sensor intact, it is safe to assume that what it is picking up is the red part of the fluorescence. Of course frame #5 with the D40x IR-720nm might be picking up UV induced chlorophyll fluorescence in the IR part of the spectrum.

[Akira]

Just checked out the TK-566 sold by hkequipment on eBay.  The front protection glass indeed looks purple.  But considering that we can "see" the purple color clearly, it is not an efficient UV-pass-VIS-cut filter.

As you would suspect, the purple color may indicate the visible light leaks in both of the blue and red ranges.  I wonder if the deep red color of the petals and the leaves were lit by the leaked red portion?  The UV-pass filters like Hoya U-330 and U-360 has the visible leaks in the very ranges.

[Øivind Tøien]

That is why to do the ball bearing test. Light leaks will show up as clear specks (directly reflecting  the LED torch light leak). Without leaks the the ball bearings look all black. Of course it is possible that if I cranked the ISO all the way up and exposed at 30sec some specks would show up, but at the distances/ISO exposures used for these shots light leaks have negligible effects.

The exposures before I added ZWB1 filter to the Tank007 in the previous post is if of course an open question. However I think light from nearby fluorescencing objects was a bigger problem with my inexperienced attempts.

[Akira]

Øivind, in fact I count on your scientific mind.  I'm looking forward to you sharing your experience!