6 replies to this topic

[Andrea B.]

Blum, A.G. 2017. Houstonia caerulea L. (Rubiaceae). Quaker Ladies. Flowers photographed in ultraviolet, visible and infrared light. http://www.ultraviol...-quaker-ladies/
Updated 24 Oct 2017: Set #3 added to post #2.
Updated 27 May 2018: Restructured common names.

Synonyms:

• Hedyotis caerulea (L.) Hook.
  
• Houstonia caerulea var. faxinorum Pease & Moore

Other Common Names:

• Bluets

Comment:
The UV-black heart of the innocent little Quaker Lady is revealed! The visible colour of this tiny flower varies from a very pale blue which is almost white to a slightly more saturated sky blue. The central structures of the flower are nicely brought out in UV.

Reference:
1. Mittelhauser et al. (2010) Bluets, page 334. The Plants of Acadia National Park. The U. of Maine Press, Orono, ME.
2. Newcomb, L. (1977) Bluets, page 156. Newcomb's Wildflower Guide. Little, Brown & Co., New York City, NY.


SET 1
Kinship Lane, Southwest Harbor, Maine, USA
15 July 2012
Wildflower

Equipment [Nikon D300-broadband + Carl Zeiss 60mm f/4.0 UV-Planar]

Visible Light [f/11 for 1/60" @ ISO 200 with onboard Flash and Baader UVIR-Block Filter]


Ultraviolet Light [f/11 for 1/60" @ ISO 200 with SB-14 UV-modified Flash and Baader UV-Pass Filter]


Ultraviolet Light: This 100% crop from the preceding photograph shows the conical cells.

[Andrea B.]

SET 2
Shore Cottage, Southwest Harbor, Maine, USA
06 July 2015
Wildflower

Equipment [Nikon D600-broadband + Nikon 105mm f/4.5 UV-Nikkor]

Visible Light [f/8 for 1/320" @ ISO-200 in Sunlight with Baader UVIR-Block Filter]


Ultraviolet Light [f/8 for 1/30" @ ISO-200 with SB-14 UV-modified Flash and BaaderU UV-Pass Filter]


Ultraviolet Light [f/8 for 1/20" @ ISO-400 with SB-14 UV-modified Flash and CopperU UV-Pass Filter]
The CopperU filter contains a liquid copper sulphate solution.


UV+Blue+Green [f/8 for 1/5" @ ISO-400 in Sunlight with UG5(1.5mm) + S8612(1.75mm)]


Infrared Light [f/11 for 1/160" @ ISO-200 in Sunlight with B+W 093 IR-Pass Filter]




SET 3
Shore Cottage, Southwest Harbor, Maine, USA
10 July 2014
Wildflower

Equipment [Nikon D600-broadband + UVPlanar ]

Visible Light [f/8 for 2" @ ISO-200 with Onboard Flash and Baader UVIR-Block Filter]
Such a small flower might best be photographed with a specialized macro lens on a camera with 40+ megapixel to better illustrate the tiny central reproductive parts.


Ultraviolet Light [f/8 for 1/30" @ ISO-400 with SB-14 UV-modified Flash and BaaderU UV-Pass Filter]
The local contrast was increased and the very dark area was slightly brightened to show the pollen grains which are much less evident in the visible photo. These edits also bring out the petal texture.

[Andy Perrin]

The UV on that one certainly has a VERY saturated blue! (Flowers are not at their best in NIR, are they? Heh.)

[Andrea B.]

That is a particularly bad IR photo! I almost didn't put it up. Shooting those long waves close up does not make for much detail. But it at least makes the point that the flower is IR-reflective.

*****

Yes, the Houstonia false blue is very intense! I treat all false colour the same in Photo Ninja. There was no push on this particular false blue. So I got curious and decided to look at the OOC and raw composites for the Houstonia. And then looked at another false blue flower for comparison.

Here are the false blue Houstonia and Angelonia. As noted, both flowers finish as a false blue. But the Houstonia false blue is definitely more intense.
^{[Both excerpts here are at early stages in the conversion, not in final form. Just going for the colour part.]}



Here are the photos as shot (mostly). I used the Nikon Neutral[0] picture control and that is preserved in these NX2 conversions. These photos have had the usual exposure tweaks (white point reset, small midtone lift, highlight control), but have had no colour edits.



The Green channels for both flowers have the darkest petals.



The Red channels have somewhat brighter petals than the Green.



The Blue channel shows the Houstonia petals brighter than the Angelonia petals (which are actually brightest in the preceding Red channel photo). The Houstonia petals are approximately equally bright in the Blue and in the Red channels.
Does any of this explain the more intense false blue for the Houstonia? Maybe? Well, probably(?). I'm going out on the old limb and saying that the strong false blue for Houstonia petals happens "naturally" -- insofar as false colours are "natural" at all.
What do you think?

[Andy Perrin]

Well, to be sure the best test would be to put both flowers physically side-by-side and shoot one photo with both in it! It's suggestive, though!

Edited by Andy Perrin, 12 February 2017 - 22:34.

[Andrea B.]

Yes, that is a good suggestion. Although these two happen to be a few hundred miles apart, I might sometime be able to match up the Houstonia with another false blue flower.

But ---- the underlying raw capture likely would not change in RGB relationships on each flower since the illumination was the same in both cases. Sunlight + SB14-mod UV flash. (Granted, the illumination cannot be exactly the same, but it is close enough for all practical purposes, as they say.) I think that the Houstonia simply has a different UV signature than the Angelonia. The Houstonia reflects more of what becomes false blue than does the Angelonia. Here are the raw histograms from a selection on each petal. I didn't get EV0 on the same place in each graph, but that does not affect the RGB relationships.
Andy, you always have interesting observations and questions.

Houstonia petal sample



Angelonia petal sample

[Andrea B.]

Updated 24 Oct 2017. Third set added in post #2. Small addition to the original Comment.