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UV Portrait
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#1 DonPilou

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Posted 20 November 2017 - 18:45

Good evening,
I keep reading all the interesting threads of this forum, but I did not found time to share new photographic work since now.
So here is a portrait taken during a cloudy day in october with the Kolari UV bandpass filter mounted on a Steinheil 50mm F/2.8 and a Canon 6D FS. The goal was to play with the limbs hit by the wind.

Attached Image: Shooting_Ihsane_HD (9) copie.jpg



#2 Andrea B.

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Posted 21 November 2017 - 04:53

The play between the leaves and the stripes on the shirt the model is wearing is fun. And she is so beautiful. Altogether quite interesting as a portrait.

I've become curious recently about the reflections seen on faces in such portraits. What is it about our human skin which cause some UV reflectivity? Is it because we only partially absorb UV? Or perhaps skin oils are reflective? Here's a selfie from Sandy which also shows UV reflectivity on the nose: http://www.ultraviol...dpost__p__17937

The bright areas on the left side of the photo distract me a little bit. I'd enjoy seeing more willow leaves hanging down there.
Andrea G. Blum
Often found hanging out with flowers & bees.

#3 DonPilou

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Posted 21 November 2017 - 08:54

Thank you ANdrea, indeed here the UV effect is not obvious. The model is from Morocco, with a clear brown skin in visible light. In UV the skin becomes very dark. The reflectivity may be due to excess of melanin here, that implies a part of reflection. I have only noticed this kind of reflectivity on brown and black skins, never on clear skins.

#4 JMC

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Posted 21 November 2017 - 12:44

Skin optics is a horrendously complex area, with a mixture of specular and non specular reflection, transmission and back scattering occuring within different layers of the skin. The oils on the skins surface are driving a lot of the observed shine, and with darker skin, this specular rerlection becomes more obvious. Any residue of makeup could also be driving the reflection if it has high oil content. Of course if it high pigment or mattifying, that'll be leading to more scattering and less specular reflection.

Edited by JMC, 21 November 2017 - 14:39.


#5 Andy Perrin

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Posted 21 November 2017 - 13:37

I actually have an entire book on it, “Biomedical Optics: Principles and Imaging” by Wu and Wang:
https://books.google...=kp_read_button

#6 Andy Perrin

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Posted 21 November 2017 - 14:13

A thought: the layers underneath the surface oils are much darker in UV. If you have a specular reflection on a light background, it will show up less than on a dark background.

Edited by Andy Perrin, 21 November 2017 - 14:14.


#7 JMC

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Posted 21 November 2017 - 14:38

Exactly, you'll still the reflection, but there'll be less contrast between the highlights and the background skin colour, so it becomes less obvious on the lighter skin.

#8 Andrea B.

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Posted 21 November 2017 - 16:15

What I love so much about UVP == we get these excellent comments from which we all learn more about our favorite activity, UV photography. Thanks to all.

Andy, can you comment further about that book? Do you like it? Would you recommend it over some other book? Just a sentence or two. Thanks in advance.
Andrea G. Blum
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#9 Andy Perrin

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Posted 22 November 2017 - 00:11

That book is highly quantitative. If you are trying to learn to write a computer simulation of how light interacts with skin (or anything else with a lot of scattering, really, since the principles are similar in other materials) then it's a great book. It is NOT suitable for a lay person, or anyone who doesn't want to get into the nitty gritty details. It does not cover situations where wave effects like interference are significant, so no iridescence and so on, but fluorescence is discussed in some detail. It was really useful to me for learning about how to simulate scattering, and also just in general how to write optical Monte Carlo simulations. (Actually, it would be possible using the programs developed in there to simulate the situation you were asking about, Andrea, and confirm the cause of the shininess, assuming the relevant skin parameters are available in UV.)