CPL Filter issue?

nycmaster

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Hello Everyone
Just got CPL filter to help with California sun. As you can see from the screenshot, there's a strange halo/rainbow effect on the top left of the screen. I thought it was my finger print on the filter so did not think too much of it. Past weekend, I washed my car and cleaned both filter and lens but the halo was still there. I also rotated the filter thinking the halo would move to bottom right corner but the halo effect still remain on the top left corner. Anyone have any thoughts?
 

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kamkar

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My bet is you have a coating or tint on your windscreen, your best option probably is to loose the CPL filter and get a flat black dashmat.
 
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nycmaster

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My bet is you have a coating or tint on your windscreen, your best option probably is to loose the CPL filter and get a flat black dashmat.
You guys are good!
That's exactly what I have on my windshield. Ceramic window tint all around my car to save me from scorching California sun. I guess no CPL for me. Honestly. I did not see noticeable difference between with or without filter.
 

kamkar

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You might also aim your camera a bit more down.
 

Dashmellow

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Hello Everyone
Just got CPL filter to help with California sun. As you can see from the screenshot, there's a strange halo/rainbow effect on the top left of the screen. I thought it was my finger print on the filter so did not think too much of it. Past weekend, I washed my car and cleaned both filter and lens but the halo was still there. I also rotated the filter thinking the halo would move to bottom right corner but the halo effect still remain on the top left corner. Anyone have any thoughts?

The rainbow effect you are seeing is a phenomenon called birefringence.

As @kamkar1 mentions the problem is likely the tint on your windshield and you may have to switch to a black dashboard mat instead of a CPL to eliminate reflections of your windshield in your videos.

What's happening is that the tint or glass tempering on your windshield is acting like a polarizer and is interacting with your CPL (circular polarizer), so the light passing through the windshield glass is being polarized twice....a camera with a polarizer looking through a polarized windshield.

The same thing will happen if you look through your windshield while wearing polarized sunglasses.

See THIS link for a full explanation and also check out the Wikipedia link above.
 
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nycmaster

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The same thing will happen if you look through your windshield while wearing polarized sunglasses.
Really? I don't see that rainbow when I look out through windshield with my polarized sunglasses on.
 

Dashmellow

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