Windows of Papilio ulysses wing scale

[Chris S.]

Scales of the Papilio ulysses butterfly--my, what big "windows" they have--around 3 microns wide!

Lens is a Mitutoyo 100x/0.70 objective I'm testing for another forum member. Quite a good specimen.

(APS-C Nikon D7100 camera, halogen light, 97 shots at 0.5 micron increment, Zerene Stacker PMax.)

Edit to add stereo:

--Chris S.

[Pau]

Wow, they are really curved!

Any chance of seeing a 100% crop test?

[Guppy]

Hi Chris

Very nice pictures of Papilio ulysses scales.
I especially like the stereo picture.

Thanks for sharing
A pleasure!

Kurt

[svalley]

Beautiful work!

Steve

[Chris S.]

Pau, Kurt, and Steve--thanks! I've appreciated your comments.

The curvature of these scales surprised me, and complicated the lighting a bit--perhaps a decent topic for a later post.

Here is a 100 percent crop, per Pau's request:

Something that experienced micro/macro photographers, such as the fellows who replied above, know well, but that newcomers to high-magnification photography may not: A lens like this 100x/0.70 is operating well into diffraction territory, in this case at f/71. This inevitably creates a fuzzy appearance due to diffraction, even while providing increased resolution (information) compared with lower NA objecives. Ironically, a lens such as a 20x/0.42 will provide less resolution, but will give a sharper appearance, than a 100x/0.70. This trade-off is inevitable, but the 100x/0.70, in this case, provided information about this subject that would not exist in the prettier rendition of a lower magnification/lower numerical aperture lens.

--Chris S.

[Pau]

Chris, thank you!

This was the idea of my request, as I wanted to see if, despite being much less crisp, the 100% crop was showing more detail than the reduced full frame. It seems, at least with this subject, that the showed resolution increase is small.

[Chris S.]

This was the idea of my request, as I wanted to see if, despite being much less crisp, the 100% crop was showing more detail than the reduced full frame. It seems, at least with this subject, that the showed resolution increase is small.

I agree, Pau. With this subject and lens, downsizing to forum resolution sacrificed little. I might even suggest that downsizing this image to forum resolution made it more pleasing to the eye: The additional information acquired by the larger NA was retained, while reduction of subjective "crispness," due to the lens' higher magnification spreading information over a larger area, was reduced.

I have been asked a couple of questions offline.

First question: "Is the intense blue color of these scales accurate?"

• Answer: Yes, the color of this scale is accurate--at least when the images leave my computer.
  
  I have a calibrated photographic monitor (BenQ SW270C). On this monitor, the colors of these scales match closely the colors of these scales under naked-eye viewing, and viewing under a low-magnification stereomicroscope. (During shooting, I see the subject only on a tethered monitor--not through the taking optics.) So I'm confident that the colors were accurate as I posted them. This said, I have no knowledge of the monitor on which anyone is viewing these images--the viewer's monitor may or may not be accurate.
  
  A cool thing about the blue color of this specimen: Its deep blue color seems robustly invariant of photographic light's angle, intensity, or even color temperature. This is quite different from most other specimens I've photographed that have structural color. In an offline conversation with Rik, he posited that this likely indicates that these scales contain photonic crystals; in my brief reading since, about photonic crystals, I think Rik is correct.

Second question: "Is the apparent curvature of the scales accurate?"

• Answer: I think so. The curvature shown matches my subjective impression when manually scrolling focus through this subject; of course, DOF is so limited that subjective impression--or "mental focus stacking"--has its limits.
  
  Here is a stereo pair (Zerene Stacker PMax) shot with a Mitutoyo 50x/0.55 objective, belonging to the same forum member whose 100x objective I was testing (his 50x is also very nice). Since the 50x has a working distance of 13mm (compared with the 100x's WD of 6mm), I was able to move the camera back and turn the subject about 45 degrees, in hopes of better showing the scale curvature.

--Chris S.

[Lou Jost]

In an offline conversation with Rik, he posited that this likely indicates that these scales contain photonic crystals; in my brief reading since, about photonic crystals, I think Rik is correct.

This group of butterflies uses a slightly different mechanism than the classic multi-layer interference that causes blue in morphos. Each "dimple" is a photonic structure. Here is a technical article about the dimples. P. ulysses is a particularly simple example. Some other Papilio species produce green light by added complexity that reflects yellow along with the blue.

https://core.ac.uk/download/pdf/12825066.pdf

https://www.researchgate.net/publicatio ... _butterfly

[Chris S.]

Lou,

Those are fascinating articles--thanks much for sharing them. Today I only had time to scan them briefly, but I have them noted for a very careful read.

--Chris S.

[David Sykes]

Chris, very nice images.

The bottom stereo image is perfect but the top one can be made even better by trying to match the central glare spot on left and right images.
The human brain immediately detects impossible disparities.
SPM can fix that or maybe a simple cut-and-paste ?

David

[Chris S.]

David,

Thanks for your constructive criticism! I appreciate it.

It's funny, how different brains process stereo. My brain can not see what David points out. But I'll try to make and post another pair adjusted per his suggestion. I'm new to stereo--this was my first.

--Chris S.

[Lou Jost]

Chris, here is a YouTube lecture about how these dimpled Papilio scales are generated by the butterfly. Amazing work. Gets interesting about 10-15 minutes in.
https://www.youtube.com/watch?v=HG96HVgOAdg

[rjlittlefield]

I notice that one of the earlier links is now dead (https://core.ac.uk/download/pdf/12825066.pdf).

But I found what I think is the same reference, via https://www.researchgate.net/publication/5495569_Sculpted-multilayer_optical_effects_in_two_species_of_Papilio_butterfly .

The RIS citation and abstract are:

TY - JOUR
AU - Vukusic, Peter
AU - Sambles, Roy
AU - Lawrence, Christopher
AU - Wakely, Gavin
PY - 2001/04/01
SP - 1116
EP - 25
N2 - The wing-scale microstructures associated with two species of Papilio butterfly are described and characterized. Despite close similarities in their structures, they do not exhibit analogous optical effects. With Papilio palinurus, deep modulations in its multilayering create bicolor reflectivity with strong polarization effects, and this leads to additive color mixing in certain visual systems. In contrast to this, Papilio ulysses features shallow multilayer modulation that produces monocolor reflectivity without significant polarization effects.
T1 - Sculpted-multilayer optical effects in two species of Papilio butterfly
VL - 40
DO - 10.1364/AO.40.001116
JO - Applied optics
ER -

Unfortunately the PDF is not hosted by researchgate.net. Instead their page says "To read the full-text of this research, you can request a copy directly from the authors."

The PDF is also available behind a paywall, at https://www.osapublishing.org/ao/viewme ... -40-7-1116 .

--Rik

[Lou Jost]

Yes!

If you do a Google search on the title (Sculpted-multilayer optical effects in two species of Papilio butterfly), you will get a list that includes a pdf at core.ac.uk. Clicking this link now raises the error message mentioned by Rik, but we know this article used to be there (see my original message). Therefore you can still access the article for free on the cached version of the site. Click the little black triangle and then click the word "cached" that appears below the black triangle. There you will have an HTML version of the article, minus the images. Maybe this link will work directly :
https://webcache.googleusercontent.com/ ... irefox-b-d

The images are very useful,, and even though they are missing from the cached html article, you can still access many of them by doing a Google image search using the title of the article. You can click on any of the images to see them in a larger window, though the full-resolution versions are paywalled.

The HTML article is easier to read if you copy it and then paste it into a blank Word document.

[micro_pix]

Awesome!

Dave