Oddly Polarized Imagery (iPhone Camera)
Apr 6, 2021 23:38:38 #
View the attached three photos before reading the explanation.
The purple windows reflections caught my eye. The sky is not that color at mid afternoon. Third photo shows those windows as seen directly by eye.
In the first photo, down lower near the tail lights, is the reflection of the scene behind the camera. The second photo shows that scene as it really looked by eye. Sky is less dramatic in the actual scene than as reflected off of the car in the first photo.
Purple color in the reflected windows is from cross polarization of the sky, as reflected first off the window, and then again off the car. Each time the image is reflected it gets polarized, once vertically and once horizontally.
The sky reflected off the car also seems polarized, single polarized, altho much of the darkening is exposure.
There is no filter on the camera. I don’t have any filters for the phone ;-)
Please DL the first photo to view it clearly:
.
The purple windows reflections caught my eye. The sky is not that color at mid afternoon. Third photo shows those windows as seen directly by eye.
In the first photo, down lower near the tail lights, is the reflection of the scene behind the camera. The second photo shows that scene as it really looked by eye. Sky is less dramatic in the actual scene than as reflected off of the car in the first photo.
Purple color in the reflected windows is from cross polarization of the sky, as reflected first off the window, and then again off the car. Each time the image is reflected it gets polarized, once vertically and once horizontally.
The sky reflected off the car also seems polarized, single polarized, altho much of the darkening is exposure.
There is no filter on the camera. I don’t have any filters for the phone ;-)
Please DL the first photo to view it clearly:
.
No Lens Filter - Double Polarized
(Download)
Sky Almost Opposite Sun - No Filter
(Download)
Windows Not Purple (mid afternoon)
(Download)
Apr 7, 2021 00:10:19 #
That is quite interesting.
--Bob
--Bob
User ID wrote:
b View the attached three photos before reading t... (show quote)
Apr 7, 2021 05:51:59 #
"The sky reflected off the car also seems polarized, single polarized"... Say What!!!??? Really?
Interesting observation you made... but is your comment true? Yes... "When unpolarized light is incident at this angle, the light that is reflected from the surface is therefore perfectly polarized." I have taken a lot of physics courses and it took UHH to educate me on this optical phenomenon.
https://en.wikipedia.org/wiki/Brewster's_angle
Interesting observation you made... but is your comment true? Yes... "When unpolarized light is incident at this angle, the light that is reflected from the surface is therefore perfectly polarized." I have taken a lot of physics courses and it took UHH to educate me on this optical phenomenon.
https://en.wikipedia.org/wiki/Brewster's_angle
Apr 7, 2021 07:56:43 #
Probably due to how the building windows are made.
I've noticed, with my polarized sunglasses, an occasional car or two in traffic have PURPLE windows.
It's due to the materials/process used to make the their windshield (windscreen).
I've never noted on what model cars that happens.
I'm hoping they don't see a purple tint to everything when they use polarized sunglasses IN their car.
I've noticed, with my polarized sunglasses, an occasional car or two in traffic have PURPLE windows.
It's due to the materials/process used to make the their windshield (windscreen).
I've never noted on what model cars that happens.
I'm hoping they don't see a purple tint to everything when they use polarized sunglasses IN their car.
Apr 7, 2021 09:24:03 #
Longshadow wrote:
Probably due to how the building windows are made.
I've noticed, with my polarized sunglasses, an occasional car or two in traffic have PURPLE windows.
It's due to the materials/process used to make the their windshield (windscreen).
I've never noted on what model cars that happens.
I'm hoping they don't see a purple tint to everything when they use polarized sunglasses IN their car.
I've noticed, with my polarized sunglasses, an occasional car or two in traffic have PURPLE windows.
It's due to the materials/process used to make the their windshield (windscreen).
I've never noted on what model cars that happens.
I'm hoping they don't see a purple tint to everything when they use polarized sunglasses IN their car.
Windscreens are usually reflecting the sky due to the angle of the glass. The sky itself is polarized at certain angles to the sun. Reflect a polarized sky off the angled widescreen and the sky is now “landscape shooter” pola-filtered. Add to that your polarized sunglasses and anything goes ! All the angles are in flux as you, your sunglasses, and the other vehicles move about.
Let’s not ignore that some cars have electro resistance heated windscreens which can reflect in odd ways.
Apr 7, 2021 09:37:02 #
User ID wrote:
Windscreens are usually reflecting the sky due to the angle of the glass. The sky itself can be polarized at certain angles to the sun. Reflect a polarized sky off the angled widescreen and the sky is now “landscape shooter” pola-filtered. Add to that your polarized sunglasses and anything goes ! All the angles are in flux as you, your sunglasses, and the other vehicles move about.
Let’s not ignore that some cars have electro resistance heated windscreens which can reflect in odd ways.
Let’s not ignore that some cars have electro resistance heated windscreens which can reflect in odd ways.
Maybe that's the reason, the heated windshield? I noticed it on some rear windows also. Not sure about the side windows.
Wouldn't account for the building windows though.
Apr 7, 2021 09:47:19 #
Longshadow wrote:
Maybe that's the reason, the heated windshield? I noticed it on some rear windows also. Not sure about the side windows.
Wouldn't account for the building windows though.
Wouldn't account for the building windows though.
Front AND rear car windows are angled about 45 degr to the sky.
Look at the non-purpled windows in the natural light shot of the white wall. It’s angled on the vertical axis at about 45 degr. The viewing angle from the lens down to the rear deck is about 45 degr on the horizontal axis. To me this looks to be a nearly perfect cross polarizing set up, close to a 90 degr cross.
Apr 7, 2021 09:59:06 #
User ID wrote:
Front AND rear car windows are angled about 45 degr to the sky.
Look at the non-purpled windows in the natural light shot of the white wall. The angle on the vertical axis is about 45 degr. The viewing angle from the lens down to the rear deck is about 45 degr on the horizontal axis. To me this looks to be a nearly perfect cross polarizing set up.
Look at the non-purpled windows in the natural light shot of the white wall. The angle on the vertical axis is about 45 degr. The viewing angle from the lens down to the rear deck is about 45 degr on the horizontal axis. To me this looks to be a nearly perfect cross polarizing set up.
Oh, I agree about the angle difference. Just though it very odd and on a very small number of cars.
I've never seen it on any of my photos that used a polarizer. Maybe because most are scenic without windows???
Apr 7, 2021 10:12:02 #
Longshadow wrote:
Oh, I agree about the angle difference. Just though it very odd and on a very small number of cars.
I've never seen it on any of my photos that used a polarizer. Maybe because most are scenic without windows???
Oh, I agree about the angle difference. Just though it very odd and on a very small number of cars.
I've never seen it on any of my photos that used a polarizer. Maybe because most are scenic without windows???
Try including some windows. Exit the woods and head on back to town :-)
Apr 7, 2021 10:12:47 #
User ID wrote:
Try including some windows. Exit the woods and head on back to town :-)
But I'm not a fan of cities...
Apr 7, 2021 11:05:50 #
Apr 7, 2021 11:10:29 #
User ID wrote:
There is no windows in Audubon PA ?
Seven...
And I must not have been at 45° to any of them.
Apr 7, 2021 12:22:25 #
This was amazing for me to read all of the responses to this posting. There really is a lot going-on here that I never knew existed and my wee-tiny brain is lost in the weeds...yet again.
WOW ! thanks guys.
WOW ! thanks guys.
Apr 7, 2021 14:21:50 #
Light reflected off a dielectric surface will be partially to completely polarized depending on the angle. The full polarization angle will depend on the dielectric material doing the reflecting. Light reflecting off a metallic surface will not be polarized. Even though the base material of the hood is metallic, it's the paint that's doing the reflecting (the light does not penetrate through the paint to the metal of the hood).
The polarization is occurring at the hood of the car by the paint, although some polarization can be occurring at the windows by the glass.
The polarization is occurring at the hood of the car by the paint, although some polarization can be occurring at the windows by the glass.
Apr 7, 2021 14:59:41 #
larryepage
Loc: North Texas area
User ID wrote:
b View the attached three photos before reading t... (show quote)
There are many novel ways in which light can be polarized and through which the color of light can be changed. My favorite was to place two sheets of polarizing film on an overhead projector with the axes of polarization oriented at 90 degrees to each other. The result was that most (but not quite all) of the light would be blocked. Now adhere a strip of transparent tape (Scotch Magic Mending Tape seemed to work best) to the bottom sheet and replace the top sheet. The tape would alter the polarization and cause light to be passed through the sheets. But...it would be colored. And the color would vary, depending on the angle it was applied relative to the orientation of the film. Rotating the films with respect to each other would change both the color and intensity of the light passing through the films. Now add more tape, so that some of it layers on top of the original tape and the angle iws different from that of the first strip. More colors. Different from each other, and different still where there are two layers of tape. As tape is added and additional layers are created, more and more distinct colors appear.
Of course, this is exactly the same effect as is seen in adjustable dichroic filters, where a range of color can be created by simply rotating one part of a multilayer filter.
The point is that as light interacts with different pigments and finishes, all kinds of things can happen. Even the tint layer between the two glass laminations in side windows (and windshields, sometimes) can produce unexpected effects observable with polarized sunglasses. There is a field of stress analysis called photoelasticity that can be used to quantitatively predict loading in mechanical parts, structural members, and other parts and systems. In fact, I am encouraged to see what effects I might be able to observe with the "pearlized" paint finish on my GM vehicle, now that you have brought it up.
Thanks for showing this to us.
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