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Polarising film

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Joined: 20 Dec 2015
Posts: 398
Location: Benavente, Portugal

PostPosted: Fri May 18, 2018 5:06 pm    Post subject: Polarising film Reply with quote

Did anyone try to polarize the light falling in the subject, rather than the reflected light ...

just got 2 pieces of polarising film, and did a quick experiment .. the resut is different but I'm not sure if I like it... Smile

With the polarising film the subject looks more "flat", but blends better with the background .. the bare picture looks to have an halo around the subject (more visible in the stick boundary) .. the polarising film decreased that halo a lot...
The reflexuon in the blue part is smaller (with film) but's more edgy..

need to experiment more, with more reflective bugs, outside daylight, bugs on reflective flowers etc ... and see what happens..

unedited pictures
RI020003 by antonio caseiro, on Flickr

Norma_raw by antonio caseiro, on Flickr

Polarized_raw by antonio caseiro, on Flickr

side by side

Untitled by antonio caseiro, on Flickr
YAWNS _ (Y)et (A)nother (W)onderful (N)ewbie (S)hooting
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Joined: 21 Nov 2009
Posts: 1249
Location: Borgholm, Sweden

PostPosted: Sun May 20, 2018 12:16 pm    Post subject: Reply with quote

The general principle is that, with only a polarizer on the light source (if any diffuser is present, the polarizer should be mounted between diffuser and subject), or only a polarizer on the lens, the visible differences with/without polarizer are caused by the surface of the subject acting as a polarizer. This is mostly the case of shiny, highly reflective non-metallic surfaces. You should rotate the polarizer to test for orientations that give the best image for a given subject.

You should see a stronger effect if you use polarizers both on the light source and on the lens. In most cases, rotating one or both polarizers in this case may strongly affect the image (exactly how, depends on the subject). It is sometimes possible to strongly reduce the reflective highlights, or at least some of the worst offending highlights, by choosing the proper orientation of the polarizers by trial and error.

If you are using coaxial illumination, then a polarizer followed (in the direction toward the subject) by a retardation plate that rotates the polarization plane by 45 degrees (called quarter-wave plate) may effectively remove the specular reflection of non-metallic subject surfaces, especially if they are not strongly tilted away from the focus plane. The principle is that the light passes twice through the retardation plate and its polarization plane is rotated in total by 90 degrees, so that light directly reflected by the subject is essentially eliminated, while light diffused by the subject has its polarization plane scrambled and part of it can always enter the objective.

Different parts of a three-dimensional subject frequently behave in different ways with respect to polarized light, and sometimes the orientation of the polarizers must be chosen as a compromise between the "best" rendering of different key parts of the subject.
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Joined: 15 Jan 2012
Posts: 4463

PostPosted: Wed May 23, 2018 10:15 am    Post subject: Polarizer Reply with quote

When I managed a camera store I sold quite a few 10 X 10 inch polarizers to artists - primarily painters. The filters cleaned up reflections when using flood lights for copy photography of flat art, but didn't intensify colors as the photographer was not using a complimentary polarizing filter on the lens. The effect is pretty much the same as cleaning up reflections in store windows.

Michael Reese Much FRMS EMS Bethlehem, Pennsylvania, USA
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