Scales of the Green Longhorn Moth

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Troels
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Scales of the Green Longhorn Moth

Post by Troels »

I was rather puzzled by the changing colors of the
Green Longhorn Moth , so after taking the pictures on location I caught a pair of animals and prepared for some studio stacks to get closer.

First I used Nikon plan 4x/0.13 on bellows with Olympus E_M5 II (m4/3).
Stack of 111 exp. at 1/4 sec. Diffused light mainly from above:

Image
Really nice blue eyes, but need a haircut!

At 4x the single scales are now visible and it becomes evident how at certain angles of incident light they appear like bright light sources. Small pieces of broken scales in the fur look like small stars.

From another angle (120 exp. at 1/6 sec.):

Image

In this view the scales on the shoulder reflect more light than the sensor can manage. I have not tried to correct the resulting stacking artifacts.

Next I experimented with different light sources at around 10x mag using
Nikon CF Plan 10x/0.30 infinity EPI + Raynox 125.

First strongly diffused light from two Jansjo lamps from above right and above left (62 exp. at 1/20 sec. FoV: 1.7mm):
Image

And then the exact same part of the wing in direct, undiffused light frontal from one Jansjo lamp as parallel as possible to the optical axis (58 exp. at 1/15 sec.):
Image

For easier comparison I made a side-by-side composition in reduced size:
Image

Talk about the importance of lightning!

Several intersting features appear.
On direct light the skin under the scales has a very strong reflektive power, almost like a safety reflex. Some of the golden scales above become almost transparent with only weak, golden lines. Without the reflex from behind they can look almost black.

With diffused light mainly from above the same scales get a strong golden glow from the same lines, sometimes oversaturating the sensor.

For me that indicates that the colors are being created by structures and not by pigments. Structures in both the skin an the scales.

There are also some nice blue scales (rounded tips), which are only blue with light from the right direction (or diffused from all directions). Combine the yellow color with the blue and you should get a green.

To make details more visible I include two 1024 px 100% crops of the same wing part in different light (a little noise reduction an very lightly sharpened):
Image

Image

At 10x magnification the effect is very clear without revealing how they perform this magic.

Notice how the long scale at the top got bent resulting in different appearance of the base part and the tip.

Would be interesting to see some 100x pictures![/url]
Troels Holm, biologist (retired), environmentalist, amateur photographer.
Visit my Flickr albums

MarkSturtevant
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Post by MarkSturtevant »

Very interesting! With these structural colors, do you find that it is hard to capture what you see through the lens?
Mark Sturtevant
Dept. of Still Waters

Troels
Posts: 600
Joined: Mon Feb 15, 2016 11:06 am
Location: Denmark, Engesvang
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Post by Troels »

An interesting question: What is the relation between what a lens "see" and what our eyes concieve? (If I understand your question right?)

The one aspect of macrophotography that continues to fascinate me is that when you get closer you capture details and structures that are very different from what you can observe naked eyed.

So I always hope to catch something I do NOT se without the lens!

By direct observation theese moths wings look like rather uniform surfaces with the ability to change their appearance from almost black to a glittering, mirrorlike white.

After enlarging the scales it becomes obvious that things are far more complicated.

1) Long scales with serrated tips are kind of semitransparent and covered with thin lines with the ability to make very strong golden reflections of light from certain angles.
2) More rounded, shorter scales with the ability to reflect stark blue light from certain angles.
3) In addition also the base skin sometimes function as a strong reflector.

Wat I am not able to capture is the sudden changes of color of the flying animals. And it would be fascinating to know how the moths themselves see al this!

As I understand it the structural colors are just as "real" as the pigment created colors: lightwaves of certain wavelengths. Neither our eyes nor the sensor can see how the waveproperties of the single photon are created.

But structural colors reveal their origin in other ways: They change their wavelength dramatically with changing angles and they can be very intense (narrow bandwith?).

To cover the gap between my visual experience and my macro captures one could dream of making a stacked movie of a moving wing at 10x - or 50x. Good luck!
Troels Holm, biologist (retired), environmentalist, amateur photographer.
Visit my Flickr albums

SteveB
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Joined: Sat Nov 25, 2017 12:12 pm
Location: Pretoria South Africa

Post by SteveB »

Fascinating!

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