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Lamium purpureum

Multispectral
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#1 Mark

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Posted 07 May 2017 - 17:04

I found a patch of these small (~4 inches tall) wildflowers growing near a local lake yesterday. The flowers haven't actually bloomed yet, but I don't know if I'll have a chance to get back there when they do, so I grabbed one while I had the opportunity. Surprisingly, they haven't wilted at all yet since I put them in a cup of water for the walk home.

Here's the VIS reference:
Attached Image: 05-06-2017_19-41-47.jpg

... the IR view:
Attached Image: 05-06-2017_19-43-47.jpg

... under UV:
Attached Image: 05-06-2017_19-36-22.jpg

... and the UVIVF view:
Attached Image: 05-06-2017_19-38-49.jpg

I think I have some work to do regarding my UVIVF images taken under UV from an MTEU303 torch. There's something suspicious about all that far-red fluorescence. I've tried including an IR absorbing filter of the torch (in addition to a U340 filter), but it didn't make any discernible difference (aside from yielding a very slightly lower exposure). For this set I shot the same UVIVF image twice - once as is (left), and once with a PTFE target in the scene (right) to use as a white-balance reference (for whatever its worth in UVIVF images). Perhaps this target is just misleading, and there really is all that far-red - it is practically all leaf and stem. I'll be trying to refine my technique further with other test subjects, for sure.
Attached Image: wbreferenceattempt.jpg

Shooting summary:
Camera
- Nikon D750 [broadband] + 50 mm Nikon series E lens + 20 mm extension tube
Lens filters

- VIS & UVIVF: 425 nm longpass + GG435 longpass + Baader UV/IR [stack]
- UV: Asahi ZRR0340
- IR: Hoya R72

Illumination/Irradiation
- VIS: Sigma EF-500 DG Super flash

- UV & UVIVF: 2 x [MTE-U303 + U340]
- IR: 40 W incandescent bulb, clear glass
Exposures
- ISO320
- f11
- 0.125-13.0s (as needed)

Edited by Mark, 07 May 2017 - 18:33.


#2 Mark

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Posted 07 May 2017 - 17:30

Update: I think this may be Purple Dead-Nettle (Lamium purpureum).

Edited by Mark, 07 May 2017 - 17:31.


#3 Andy Perrin

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Posted 08 May 2017 - 01:36

The stem is interestingly purple in the UV, compared to the silvery leaves.

#4 OlDoinyo

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Posted 08 May 2017 - 01:51

Leaves and stems look very mint-like. Do other mints and spurflowers give similar results?

#5 Cadmium

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Posted 08 May 2017 - 07:47

View PostMark, on 07 May 2017 - 17:04, said:

I think I have some work to do regarding my UVIVF images taken under UV from an MTEU303 torch. There's something suspicious about all that far-red fluorescence. I've tried including an IR absorbing filter of the torch (in addition to a U340 filter), but it didn't make any discernible difference (aside from yielding a very slightly lower exposure). For this set I shot the same UVIVF image twice - once as is (left), and once with a PTFE target in the scene (right) to use as a white-balance reference (for whatever its worth in UVIVF images). Perhaps this target is just misleading, and there really is all that far-red - it is practically all leaf and stem. I'll be trying to refine my technique further with other test subjects, for sure.

I think the red foliage is normal for UVIVF.
Isn't red well within the visual spectrum?
Doesn't chlorophyll fluoresce red?
Is PTFE the best WB target to use for visual range? (minor point)

#6 Andy Perrin

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Posted 08 May 2017 - 15:01

Quote

Is PTFE the best WB target to use for visual range? (minor point)
It looks really white to me? Does it not look white to you -- actual question considering I have red/green colorblindness issues? But I would think that anything that looks white to a human without colorblindness would make a good white balance target for visible.

#7 Mark

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Posted 08 May 2017 - 16:48

@OlDoinyo: I haven't photographed mints yet, so I don't know - but its a good idea for something I can try next.

@Cadmium: Red, simply speaking is of course visible. I use the term far-red in reference to chlorophyll fluorescence because it straddles the border of infrared, so far up the visible EMS (towards the longer wavelength direction) that it is difficult to see, even under ideal lighting conditions (dark room, special lighting, etc). Also consider that not everyone can see the extents of the EMS to the same degree; which could make this far-red more/less difficult for any given person. I don't know if it is true, but I do remember reading years ago that some small percentage of women are able to see measurably further into red (far-red) than men, albeit only slightly further. Personally I question that claim. But the point is, I only say 'far-red' because of its proximity to the limit of our detection. As a side note I'd like to add, the first time I got a good look at chlorophyll fluorescence was when I extract some into a vial of acetone for a photo experiment. And when I turned out the lights and turned on the UV - wow!, it was so red, so very very much more red than anything I had seen before. It was a little tough to see, and took my eyes a bit of time to acclimate, but it was very cool. Something I still enjoy seeing to this day.

As for the PTFE WB target question... well, you're right to question it. I myself question its use - as far as its application to UVIVF imaging. I still haven't yet quite figured out if the PTFE is fluorescing, or simply reflecting/scattering violet/blue light effectively - but either way it does appear to have some sort of glow under any/all of my UV lights. Still, its the best I can do for now, in PP to get rid of any residual purple light bleed from whichever UV source I happen to be using to excite the fluorescence. Though I have found it not to be ideal. It does introduce an strong color shift, often times so much so that it is not useful (IMO). Now that I'm thinking of it, I just got an idea/realization... for many of my past UVIVF (and multispectral sets) I've propped my subjects on a black porcelain plate - which does not fluoresce at all, and appears black or nearly black under almost any lights I put it under. Maybe I can white balance off that more effectively. I'll give it a try during my next shoot.

@Andy: the PTFE does wind up looking white, because I've set the WB from it - though it doesn't start that way of course. And, the color shift it introduces is often overwhelming. I think the subject of white balancing UVIVF images is actually a bit complicated, certainly more so than I'm interested in... I just want to make nice images!

#8 Andy Perrin

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Posted 08 May 2017 - 18:49

View PostMark, on 08 May 2017 - 16:48, said:

@Andy: the PTFE does wind up looking white, because I've set the WB from it - though it doesn't start that way of course. And, the color shift it introduces is often overwhelming. I think the subject of white balancing UVIVF images is actually a bit complicated, certainly more so than I'm interested in... I just want to make nice images!
I don't mean "does it look white in the camera/computer after setting a white balance with it," I mean "does it look white to your human eyes, even if you left your camera at home?"

You should white balance with it under visible, while it's not illuminated with UV at all, then there will be no PTFE fluorescence issue. (Or maybe I'm not understanding the problem here.)

Edited by Andy Perrin, 08 May 2017 - 18:53.


#9 JCDowdy

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Posted 08 May 2017 - 20:48

Virgin PTFE or Spectralon appear dark under UVIVF unless contaminated or simply reflecting extraneous Vis or VF emission(s). The pervasive dust is always bedeviling in that regard.

The main problem is with UVIVF is what you see is rarely what you get, mainly due to human visual accommodation. I suggest you try your in-camera daylight WB since Daylight balanced film has historically been the standard for film based fluorescence photo-microscopy.

I recall we have discussed this topic previously and it is also now in the relevant Sticky

#10 Cadmium

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Posted 09 May 2017 - 07:42

I think the question of what is a true visual white in UVIVF is interesting.
I tried a few things tonight, some where more earthy, some were more blueish, but the most white to my eye was some Arm and Hammer toothpaste. Some of the white to that is actual florescence I think, because it actually remains luminescent briefly after the UV is removed. The second most white thing I found was a PEC Pad, but still a bit blue to the eye when compared to the tooth paste.
I tried a number of other materials, baking soda, aragonite, calcium carbonate, crushed coral, salt, all of which are much more white than PTFE to the eye, but none of which are really white to the eye.
PTFE looks dark, gray, but a little brown almost to the eye, and a bit on the purple edge with no torch filter.
Interestingly, I tried both pink and white versions of cerium oxide, which looks very purple with no torch filter (U-340 x 2mm), and very very dark red, basically black using a filter torch. Quite interesting in the dramatic difference in color and lack there of between the filter and no filter.

Anyway, I am certain there is something that looks absolutely white to the eyes in UVIVF. I think if we could find something that looks white to the eye, then it could be used as a white balance standard for UVIVF.
Maybe Shane would know.

Edited by Cadmium, 09 May 2017 - 09:41.


#11 Andrea B.

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Posted 09 May 2017 - 12:51

You are asking for a substance which absorbs UV and fluorescently emits Visible white. That is, it would emit simultaneously equal amounts of blue, green and red. Tough thing to find.
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#12 JCDowdy

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Posted 09 May 2017 - 22:00

View PostCadmium, on 09 May 2017 - 07:42, said:

Anyway, I am certain there is something that looks absolutely white to the eyes in UVIVF. I think if we could find something that looks white to the eye, then it could be used as a white balance standard for UVIVF.

I do not understand why one needs this, are you finding in-camera standard Daylight WB setting unsatisfactory in some way?

#13 Cadmium

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Posted 09 May 2017 - 22:52

Just and idea, sorry. ;-)

#14 Andrea B.

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Posted 09 May 2017 - 23:12

I find in-camera Daylight WB somewhat unsatisfactory for UVIVF. After all, fthere is rather a wide K range for what is considered "daylight". When sitting in the dark shooting UVIVF how do we determine which K to use? I suppose Daylight WB is close enough for most practical purposes, as they say...... B) :lol:.
Sometimes I strive too hard for perfection. :wacko: :blink:
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#15 OlDoinyo

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Posted 10 May 2017 - 03:24

Could a fragment of a fluorescent bulb/tube with a suitable phosphor mixture serve as a standard? Of course, I don't recommend intentionally breaking them, due to the mercury vapor issue, but if you happen to know of an already-broken one, well...

#16 JCDowdy

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Posted 10 May 2017 - 14:06

View PostAndrea B., on 09 May 2017 - 23:12, said:

I find in-camera Daylight WB somewhat unsatisfactory for UVIVF. After all, fthere is rather a wide K range for what is considered "daylight". When sitting in the dark shooting UVIVF how do we determine which K to use? I suppose Daylight WB is close enough for most practical purposes, as they say...... B) :lol:.
Sometimes I strive too hard for perfection. :wacko: :blink:

This is an interesting question. What is it that you find unsatisfactory? May I assume it that the image does not capture what you are seeing? Perhaps that is because Daylight WB doesn't reproduce your dark adapted color perception.

Dark adapted color perception begins to occur at least 5-10 min of darkness but is supposedly not at maximum until 30 min. I guess any UVIVF colors observed inside that time frame might also be in the process of changing. I also suspect that the act of observing UVIVF colors under darkroom conditions may alter dark adapted color perception.

Wikki Pete calls this the Purkinje effect (sometimes called the Purkinje shift or dark adaptation) is the tendency for the peak luminance sensitivity of the human eye to shift toward the blue end of the color spectrum at low illumination levels.

An Incandescent/Tungsten WB looks blueish in sunlight. So if the goal is to simulate dark adapted color perception, would a bluer Incandescent or Tungsten WB be closer to what is seen? I know that in some cameras, such as my Panasonics, you can bias a WB more to the blue.

Perfection is never attained, only approached. The mathematician recognizes this relationship as asymptotic.

#17 Cadmium

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Posted 10 May 2017 - 18:29

Actually, I have a 1/4" thick sheet of nylon. Under regular light it looks a very pale shade of tan or flesh color, but shine the MTE on it in a totally dark room, and it looks more white to the eye than anything else I have found so far,
even whiter than the toothpaste.

#18 Andrea B.

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Posted 14 May 2017 - 19:56

This is an interesting question. What is it that you find unsatisfactory? May I assume it that the image does not capture what you are seeing? Perhaps that is because Daylight WB doesn't reproduce your dark adapted color perception.

John, your comments are right on. Yes, I don't seem to capture what I'm seeing. And yes, it would certainly seem to be because of some "conflict" between scotopic and photopic vision. I've struggled with the notion of color accuracy in UVIVF photos since I learned how to make them.

After I make the photo while in the dark closet, I try to review it on the LCD. But the LCD light alters perception, of course. And (eventually) on the computer monitor, the photo looks different, yet again.

So how do we solve this? I don't know. I think that perhaps we can only choose a K value with which to shoot and then make it known when exhibiting the photo along with applying the understanding that the actual fluorescence may be perceived slightly differently in the dark. For now, Daylight 5500 seems to be the only way to go. :lol:

And so far I feel that my UVIVF photos are at least in the ballpark w.r.t color accuracy. For example, fluorescent chlorophyll shows as some kind of red and not magenta or blue or orange. I think we ought to at least try for this ballpark color accuracy, yes??
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#19 JCDowdy

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Posted 15 May 2017 - 17:04

View PostAndrea B., on 14 May 2017 - 19:56, said:

I think that perhaps we can only choose a K value with which to shoot and then make it known when exhibiting the photo along with applying the understanding that the actual fluorescence may be perceived slightly differently in the dark. For now, Daylight 5500 seems to be the only way to go.. ........ I think we ought to at least try for this ballpark color accuracy, yes??

Yes, absolutely my point. Imagine how different one's perception would be if shooting tethered from outside the dark enclosure. That might not be that difficult actually, and if UVI is shortwave even a necessity!

Color standardization cards for IVIVF do in fact exist and I suppose the accompanying software enables something like custom color profile. However I cannot justify investing US$875 unless for professional use.

#20 Andrea B.

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Posted 15 May 2017 - 17:53

WOW !!!! Thank you thank you thank you !!!!!!!!!!!!!!!!!!!!! Soooooo cool.
Andrea G. Blum
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