Circular Polarizers and Rainbows - Just Say No

I recently started using a CPF outdoors. Never did before, but everyone swears by them for landscapes and I do notice that I can get better skies for sure. So, I'm down in FL visiting my Mom and she's yelling at me to come outside and take a photo of this rainbow. I grab my camera, go out, raise the camera and I'll be damned if there's no rainbow in the shot. I see it, I take it with my iPhone and get it, but nothing on my camera.

Next day, I'm driving in and there's a perfect, strong double rainbow over her house, so I grab the camera and go to shoot it - it's faded and incomplete. Took me about a minute to realize, "Dumbass - it's the CPF!!" If you're curious why this is, the very direction of sunlight that I want to filter to make the skies pop is the direction that produces the rainbow.

I didn't have time to take it off, but as I turned it there it was, though I couldn't capture the entire arc with the same level of intensity. So, word to the wise. If you use a CPF and see a rainbow, get it in your head that the first thing you want to do is take it off.

Interesting

I was watching videos about this just last night.
Here is one that demonstrates that.


Circular polarizing filter disappears the rainbow - YouTube

I disagree. I always leave mine on for rainbows. It is true it WILL disappear if you turn the filter but as you go thru the 360deg turns it will also reappear.......as the above little vid shows. The CPL makes the colours better, as it is my understanding that a rainbow is polarised light and using a polariser enhances that polarised light depending on how the CPL is set (I'm not very scientifically minded so may not be explaining it correctly).

Vixen said:

It is true it WILL disappear if you turn the filter but as you go thru the 360 deg turns it will also reappear...

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Pretty much this. ^^^

Adjusted one way, the CPL will diminish the intensity of, or remove, the rainbow; turn it further and the colors will be enhanced.

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I'm thinking when it reappears, it is then un-polarized at which point it would be the same as no CPL to begin with. Or, the light loss just from having a filter on when un-polarized is making the colors appear darker.

Rick M said:

I'm thinking when it reappears, it is then un-polarized at which point it would be the same as no CPL to begin with.

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I don't think a CPL is ever not-polarizing. I could be wrong but from what I can tell it's not a matter of "if", only a matter of much.

Rick M said:

Or, the light loss just from having a filter on when un-polarized is making the colors appear darker.

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Since the filter sits in front of the lens any light loss is compensated for by the exposure meter.

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The rotation becomes directional in its polarization. So, with small rainbows it may make colors pop, but with large rainbows spanning the frame it compromises the consistency of the color across the span - more intense at the midpoint and fading at the edges. I know, I tested it.