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UltravioletPhotography

[Filter Test] Hoya U340 vs BaaderU :: crocuses in the wind


Andrea B.

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Hi everybody, our favourite eBay seller of uviroptics filters sent me this diabatic chart of these same discussed filters.....

Col

 

post-31-0-61018500-1428199161.jpg

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That is the internal transmittance. To get the transmittance we need to multiply by the reflection factor. You could use the Reflection Factor of a UG-11 (0.91) on the U-340. The Reflection Factor of the S-8612 is also 0.91.

 

While that means the transmission is lower in the UV, it is also lower in the IR. The best peak of 70% would be 63.7%.

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Col & Steve - thanks for the good charts !!!

Reed - thanks for the reminder about reflectance factor !!!

 

The thing is --- I'm more interested in the bandwidth than I am in the transmission. The U340+BG39 moves bandwidth to the right. Why that should cause some cyan/green tints I don't know.

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Andrea,

 

I have a theory. The closer you come to 400nm, the more solar UV is available. The drop in solar UV is quite sharp. See image below.

http://qdl.scs-inc.us/2ndParty/Images/Charles/Sun/SolarSpectrum2_wbg.png

 

Thus, while the transmission peak is less for the U340+BG39, the percentage of solar UV in the 370-400nm range - as a percentage of all your total UV striking the sensor - is greater than with the other filter combinations. My theory is that those tints are from that range.

 

(I have a theory for everything.) :)

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Reed, you stepped on one of my pet peeves! You mean "hypothesis" not "theory"! :)

 

However I agree that both the UV source as well as the particular filter transmittance be considered. I find it interesting that the shadow of the petal on the right also appears greenish to my eyes, particularly the U340+BG39. This recalls comments I made some time ago about the potential spectral difference between directly reflected UV and reflected scattered UV from shadow.

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You might try to take a picture during dawn (the sun just down, blue sky),

then there is only scattered light and UV gets (dark) green-yellow

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John,

 

No, I have a theory... :)

 

1 : the analysis of a set of facts in their relation to one another

2 : abstract thought : speculation

3 : the general or abstract principles of a body of fact, a science, or an art<music theory>

from Merriam-Webster Online

 

I used the first and second definition above, you are using the third. We are both right according to the context. Had I been writing in a scientific journal, I would carefully use your definition. Unfortunately, I can assure you that "theories" I might generate will never be capitalized by the scientific community. :)

 

I did not propose a hypothesis for testing. As Merriam-Webster Online defines "hypothesis", a hypothesis is a call to action (b below):

1 a : an assumption or concession made for the sake of argument

b : an interpretation of a practical situation or condition taken as the ground for action

 

The etymology of the two words is also interesting:

theory - 1590s, "conception, mental scheme," from Late Latin theoria (Jerome), from Greek theoria "contemplation, speculation; a looking at, viewing; a sight, show, spectacle, things looked at," from theorein "to consider, speculate, look at," from theoros "spectator," from thea "a view" (see theater) + horan "to see," possibly from PIE root *wer- (4) "to perceive" (see ward (n.)).

 

hypothesis - 1590s, from Middle French hypothese and directly from Late Latin hypothesis, from Greek hypothesis "base, basis of an argument, supposition," literally "a placing under," from hypo- "under" (see sub-) + thesis "a placing, proposition" (see thesis). A term in logic; narrower scientific sense is from 1640s.
both from etymonline.com

 

Sorry, folks, I enjoy etymology. :)

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Of course I am biased toward using the scientific definitions. In that context, hypothesis is conjecture, an untested explanation, while theory is an accepted explanation strongly supported by evidence. It is unfortunate the common vernacular tends to consider the terms synonymous.
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Pentax K5 + UAT 85/4.5

Photo Ninja white balance [made on same area in each photo.] made from corresponding fotos of white standards.

Saturation pushed to better illustrate differences between the filter stacks.

 

Added: I did not take white balance from the white standard in these fotos because it was on the side and might have been subjected to vignetting or edge effects. So it doesn't really look white in some of these fotos. Well, geez.

 

BaaderU

f/4.5 for 1/1.2" @ ISO-640

uat_ccPassport_uvBaadSun_20150405wf_142pn.jpg

 

Hoya U340 (1mm) + S8612 (1.75mm)

f/4.5 for 2.5" @ ISO-640 EV+1

uat_ccPassport_u340bg8612Sun_20150405wf_163pn.jpg

 

Hoya U340 (1mm) + BG39 (~2mm)

f/4.5 for 2.5" @ ISO-640

uat_ccPassport_u340bg39Sun_20150405wf_191pn.jpg

 

Hoya U340 (1mm) only = UV + IR

EDIT: The original version was replaced with this more accurate version.

f/4.5 for 1/25" @ ISO-1000

uat_ccPassport_u340Only_20150405wf_203pn.jpg

 

Visible Comparison with Baader UV/IR Cut

Saturation was not pushed.

f/4.5 for 1/160" @ ISO-160

uat_ccPassport_visSun_20150405wf_119pn.jpg

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Andrea,

 

What was the lighting in the last shots?

 

And what is the thickness of the Hoya U-340?

 

Thanks.

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All fotos were made in natural sunshine on my porch. It is a screened porch, but the screening does not seem to cut the sunshine by much. I will go back and edit and add some exposure data.

I also added a visible shot.

 

I've just checked all the filters used to get their thicknesses:

 

Hoya U340 = 1mm.

Schott S8612 = 1.75mm.

B+W BG39 in F-Pro mount = 1.8 to 2mm, as per B+W literature.

 

Just wondering if there is some reason you asked? Let me know, of course, anytime you (or anyone else) spots any errors or other problems. "-)

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This is the diabatic chart of the above filters, I was given, so I can learn something about what is being shown here....

 

post-31-0-09182400-1428370200.jpg

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Thanks for nice chart.

 

It is clear that the U340+BG39 records mostly between 340-380nm while the U340+S8612 records mostly between 320-380nm. However, it is still is a mystery to me why the U340+BG39 combo should induce greenish/cyanish tints. :)

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  • 1 month later...
igoriginal

Hi there, Andrea! And hello, to everyone else, as well.

 

Been a long time, since I have been absent from UVP, in general. I'm just making my way back, now, after a crazy past winter and spring season with other work.

 

I've seen this "phenomenon" before, particularly with visible-white flowers, using a U-340 + BG40 stack. I suspect that the same response is occurring with your U-340 + BG39 stack.

 

So, what's going on here, in my opinion? In simple terms, I have grown to suspect that white flowers in particular (though probably not always) exhibit a substantially higher IR-reflective nature, compared to all other visible-colored flower petals. That is, the absence of pigmentation make them far more IR-reflective, compared to pigmented flower petals. And, in the case of when you have a UV-pass/IR-block stack where the IR-block glass is just barely suppressing the IR, what may be happening is that the exceptional IR "spike" from IR-reflective white flowers otherwise crosses that IR-suppression threshold. If only by a nominal amount. But this nominal amount (while not outright flooding the overall image with IR), is just enough to shift the UV-neutral color response away from blue/indigo, and towards the green end.

 

Now, I remain no expert in spectrography, of course. Thus, this is an under-trained and informal statement of mine. Still, based on my own experiences, I see no better explanation than this one: That visible-white flowers in particular are like the "neutron stars / pulsars" of the flower world, when pertaining to the IR-spectrum. Their IR-reflectance can far exceed other petals which possess coloration (just as neutron-star and/or pulsar radiation emission and hence their brightness can far exceed the otherwise typical star, and even just about any other interstellar object). So, when a UV-pass/IR-block stack just barely suppresses adequate IR to yield a "proper" (UV-neutral) image, the IR energy reflected from white flowers can "punch" through that adequacy, if only affecting those parts of the image expressly pertaining to the white-only flowers (but not affecting any other flowers with visible coloration).

 

I have supported my own hypothesis, due to the fact that when I obtained other thicknesses of BG40 (in my case, 2.5mm-thick BG40, instead of the 2mm-thick BG40 which I was using), this phenomenon was finally attenuated for, and vanished from the resulting image.

 

My conclusion (for the time being), is that plant pigmentation (on petals, at least), seems to play a significant role in the reduction of total IR-reflectance, due to the variable absorption taking away from the total reflected IR energy. Thus, with flower petals which lack any apparent pigmentation (white petals), the IR energy is left to reflect a substantially higher peak (aside from accounting for other potential IR-absorptive variables, such as flower texture, angles of display in relation to the sensor, moisture content, etc.)

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Hi Igor!

Is this a correct statement of your hypotheses?

Hypothesis: White flowers have stronger IR reflection than pigmented versions of the same flower.

 

So, first we need to find some examples of flowers having both white and pigmented versions.

Examples -

spring: crocus, tulips

summer: alyssum, cosmos, impatiens, lilies, phlox, vinca, and zinnia (Profusion strain)

 

Then IR reflectance must be measured.

I suppose one could make IR photographs of the white & colour versions side-by-side and see if the white version is brighter? That is not proof but would lend some support to the hypothesis and perhaps make for an interesting post here on UVP. ;)

 

Before attempting any measurements or tests, however, it might be worthwhile to read up on what causes IR reflectance in plants/flowers. Well, OK, there is nothing to absorb it, duh. But it could also be that conical cells help scatter the longer waves?

 

Brief review of plant pigments: chlorophyll, carotenoids, flavonoids, betalain.

Chlorophyll - green in leaves.

Carotene, xanthophyll (carotenoids) - yellow, orange, red.

Anthocyanin (flavonoids) - red, magenta, purple, blue.

Betalain - yellow, red - only in Carophyllales (cacti, amaranth).

So white flowers contain no pigments or very low amounts of pigment.

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Thanks Andrea & Hi Iggy

Thanks Andrea for the encyclopedic reference to IR reflectance of flowers ;)

IR appears to mostly reflect from just below the surface of organic matter, including our skin, actually about 1mm below the surface of our skin.

Dark skinned individuals look white in IR light, pink skinned individuals look like ghosts in IR light. Surface features like, moles, freckles, wrinkles & stretch marks all disappear in IR light.

I would hazard a guess & say the same might be happening with plants & flowers.

Cheers

Col

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I suppose the IR is reflected because it goes a bit beneath the surface, so refractive index changes - and there are no absorbing pigments/chemicals with which it can interact.

 

I get that IR is not useful to the leaves for food manufacture (chlorophyll needs blue & red light mostly), but I'm not sure why flowers all reflect it. Maybe lower energy light is just not useful for anything in the flower. There are some small exceptions - gazanias absorb a bit of near IR and a tiny bit of longer IR.

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