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Cross-polarized Bomarea seedpods

 
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Lou Jost



Joined: 04 Sep 2015
Posts: 3617
Location: Ecuador

PostPosted: Sun Sep 02, 2018 6:58 pm    Post subject: Cross-polarized Bomarea seedpods Reply with quote

I made some photos of a drying Bomarea seedpod I found at 3600m elevation on my local volcano, Tungurahua. I am posting it (straight out of Zerene, no retouching) to add another example of cross-polarization to the forum. Photos are on an Olympus MFT 20Mp sensor, Oly 60mm macro, camera-controlled focus-bracketing. Background is Protostar; cross-polarization eliminated much of the glare from that.

The first image is unpolarized:



The next image is cross-polarized, then slightly backed off from complete cross-polarization; I think some reflections are useful:

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Lou Jost



Joined: 04 Sep 2015
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Location: Ecuador

PostPosted: Sun Sep 02, 2018 7:04 pm    Post subject: Reply with quote

Here is what it looked like before I collected it. It was in very diffuse light on a foggy day:

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JohnyM



Joined: 24 Dec 2013
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PostPosted: Mon Sep 03, 2018 3:40 am    Post subject: Reply with quote

Huge improvement indeed. How did you implemented polarization into your setup?
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Lou Jost



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Location: Ecuador

PostPosted: Mon Sep 03, 2018 5:41 am    Post subject: Reply with quote

Just a sheet polarizer over a flat LED diffused light (diffusion must occur before the light hits the polarizer), and another polarizer on the lens.
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JohnyM



Joined: 24 Dec 2013
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PostPosted: Mon Sep 03, 2018 6:43 am    Post subject: Reply with quote

Simple, yet effective, but i can imagine you could also get big improvement with bigger light source. And those techniques are hard to implement toghether.
One would need to use lens instead of diffuser sheet to retain polarization if polarizer is placed on light source. Or obtain large polarizer sheets to cover big diffusors. I've been thinking of implementing this technique outside of Epi microscope, but so far couldn't produce satisfactory results on ergonomic friendy setup.
Getting correct angles on multiple large light sources is also quite a pain.
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Lou Jost



Joined: 04 Sep 2015
Posts: 3617
Location: Ecuador

PostPosted: Mon Sep 03, 2018 6:54 am    Post subject: Reply with quote

Use one big polarizer sheet close to the subject rather than many small ones on individual light sources. One of my sheets is about 40x50cm, big enough for anything.

Yes, bigger light source also helps! Godox translucent plastic domes work very well.
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