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UltravioletPhotography

Seeing through the Fog


Andrea B.

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Fog has been rolling in and out all day over Somes Sound. So I thought it would be a good time to test again the properties of basic Visible, IR and UV filters. The scene was not chosen for compositional effect (obviously), but rather for its fog and distance and inclusion of water, trees and sky.

 

The results of a fog & distance shoot like this are always interesting. In this array of photos, we can see clearly that the longer IR wavelengths penetrate the fog much better than the shorter UV wavelengths. No surprise there. However, I'm not sure I have worded this correctly. Should we instead say that the shorter UV wavelengths are more scattered than the longer IR wavelengths? Weigh in on this, please!

 

More detail is revealed in the IR photo than in the Visible or UV photos all of which have lots of details obscured by the fog -- especially the UV shots. This is all the reverse of the results obtained when I'm shooting floral close-ups indoors. Those flash-lit flower close-ups typically reveal immense surface detail in the UV with the IR being the softest and least detailed and the Visible in between the UV/IR extremes.

 

The fog was constantly shifting so different areas are obscured in each frame.

 

White balance was set in-camera for each filter. Conversion was made in Photo Ninja using a Pentax K5 profile which preserved that white balance. A bit of sharpening was added, but no other edits were made because I wanted to present basic results for the sake of comparison.

((Were I to display these photos as finished photographs, I would have made some curve tweaks and perhaps have opened up a shadow or two.))

 

Well flapdoodle. I see some dust bunnies or spots of something. I just cleaned that K5!!

 

Equipment [Pentax K5-conversion + Asahi Ultra-Achromatic-Takumar 85/4.5]

 

Infrared [f/11 for 1/15" @ ISO-80, Aperture Mode EV+0.0, Schott 830nm IR-Longpass Filter]

So much more of the wave action is revealed in this IR frame.

Is that because we are seeing underneath the water surface a bit?

fog_irSchott830_sun_20170717somesSoundSwhMaine_02pn.jpg

 

Visible [f/11 for 1/200" @ ISO-80, Aperture Mode EV+0.7, Baader UVIR-Cut Filter]

fog_vis_sun_20170717somesSoundSwhMaine_pn.jpg

 

Ultraviolet [f/11 for 1" @ ISO-80, Aperture Mode EV+1.0, BaaderU UV-Pass Filter]

The dark dots in the water are lobster buoys or mooring floats.

fog_uvBaad_sun_20170717somesSoundSwhMaine_03pn.jpg

 

Ultraviolet [f/11 for 1.3" @ ISO-80, Aperture Mode EV+1.0, StraightEdgeU UV-Pass Filter]

fog_uvStraightE_sun_20170717somesSoundSwhMaine_03pn.jpg

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Fog droplets are relatively large and tend to reduce visibility either by direct obscuration or by Mie scattering. Thus, the wavelength dependence is modest, as can be seen here and elsewhere. With smaller particles (haze,) the difference becomes much more dramatic, as Rayleigh scattering becomes a factor.
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Andy Perrin

Adding to that: Mie scattering is the more general theory; Raleigh scattering is just the limiting case of Mie scattering when the droplets are much smaller than the wavelength of the light in question. So it's ALL Mie scattering really!

 

The IR penetrates better BECAUSE it's scattered less (for droplets of the same size). There is also absorption to consider, though, with regard to penetration.

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Thanks!

I've been reading up on it now. And have learned about small particles (of whatever) causing Rayleigh scattering and large causing Mie scattering. Quite interesting stuff.

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  • 5 years later...

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