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Polarised filter needed for photographing cars?


mikehit 11 8.0k 13 United Kingdom
7 Jun 2014 9:14PM
It does not remove reflections but removes (or reduces) glare - in fact by removing glare you are more likely to see the underlying reflection (water gives a much better illustration on this).
oldblokeh 10 1.2k United Kingdom
8 Jun 2014 8:34AM

Quote:I thought polarisers didn't remove reflections from metal?



Quote:It does not remove reflections but removes (or reduces) glare - in fact by removing glare you are more likely to see the underlying reflection (water gives a much better illustration on this).



Specular reflection from materials that are dielectrics (most electrical non-conductors, including water) tends to be polarised in a direction parallel to the reflecting surface, depending on the angle of incidence of the light. At a critical angle, the Brewster angle, all the reflected light will be polarised. So a polarising filter, by blocking light with that orientation of polarisation, does reduce/ remove the reflection. Whether you call it glare is simply a matter of intensity.

Polarising filters will not help with reflections from metal, as they are not dielectrics. Most mirrors consist of a metallic film behind a glass sheet. The reflection from the metal will not be polarised, but reflections also occur from the glass, albeit of a lower intensity, Depending on the angle, these will be polarised.

The Brewster angle is related to the ratio of the refractive indices of the two media in question, e.g. air and water or air and glass. For water/air it's about 53 degrees and for glass/air it's about 56 degrees

By the way, circular polarising filters comprise a normal linear polarising filter sandwiched with what's called a quarter wave plate that circularly polarises the output from the linear filter.
oldblokeh 10 1.2k United Kingdom
8 Jun 2014 9:18AM
Here's an example I just shot to show the difference between metallic and non-metallic specular reflections. The left half is without filter, the right half is with. Note how, in the left image, the glass door is showing a mirror-like reflection just like the actual mirror above it. In the right hand image, the actual mirror appears unchanged, while the reflection in the glass door has been almost entirely removed.

polariser.jpg
Evertonian 8 729 England
8 Jun 2014 10:55AM
Excellent example shown above.
saltireblue Plus
11 11.8k 75 Norway
8 Jun 2014 11:01AM

Quote:Excellent example shown above.

Beat me to it...
8 Jun 2014 12:08PM
Strangest car I've seen Smile

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