What's causing this effect? Polarizer?

Hovik · Oct 9, 2015

Hi everyone, just a quick question. I do mostly auto photography and recently I've noticed this rainbow light effect on windshields and headlights of cars. Sometimes it's really severe and looks terrible.

70-200 F4 IS on 5D3 with B+W Polarizer MRC Filter

16-35 F4 IS on 5D3 with Kenko Filter.

I don't remember having this issue with my 5D2 previously, just got the 5D3 recently and the above shots are some of the first taken with it.

Another shot from last week, also with 70-200:

It doesn't look good and creates more post processing work to get rid of it. Any idea what could be causing this? I'm no pro, so if it's a very simple answer, please forgive me! lol

THANKS

jcdeboever · Oct 9, 2015

It is the UV / Anti Glare coating built into glass and plastics. I have polarizing sun glasses that I wear and I can see the same thing your camera does while wearing them. As far as how to eliminate it, I am not sure. I just wanted you to know what it was. Hopefully someone on here can tell you how to correct it.

Braineack · Oct 9, 2015

its the CPL. but you should have it rotated so it doesn't do that...

480sparky · Oct 9, 2015

I doubt rotating a CPL will eliminate the effect. More likely, you'll need to remove it.

TCampbell · Oct 9, 2015

Polarization often causes that when shooting curved glass, plastics, etc. Stress points get that rainbow-like effect.

All these forum posts that ask about Lightroom vs Photoshop... This is one time when I'd probably take the image into Photoshop. You can creat a mask in Photoshop and then desaturate the image to remove it. A quick way to inspect this is to switch to the channels tab in Photoshop and inspect the "Luminence" channel. If that channel looks good, then creat a mask. Edits will not be applied to masked-off areas. This would allow you to remove the color only from the effected areas.

You might be able to brush it out in Lightroom. (Lightroom will let you brush on the desaturation effect and you could tell it to "detect edges" so it doesn't go beyond the headlight lens or windshield.)

What brand polarizer are you using?

TCampbell · Oct 9, 2015

I missed that you have a B+W brand filter. They're excellent. But based on the windscreen glare it looks like you haven't rotated the filter to the correct orientation to kill the reflection.

Also... if you're shooting in one direction, tune the filter for it, take a bunch of shots, then turn to face a new direction, you must re-tune the filter. The polarization is based on the reflection angle from the light source. When that angle changes (e.g. You are facing a different direction) then the previous tuning won't work and you must re-tune.

Hovik · Oct 12, 2015

Thanks, Tim. I'm aware of the need to rotate the filter and do it all the time before taking the shot. I'm also able to quickly remove the effect in Photoshop by de-saturating a layer and applying masks. I just don't remember having this issue before on either my 7DII or 5DII. I doubt this is a camera body issue, but the lenses are the same ones, so not sure what's changed.