POLARIZER PROBLEM - Changing HUE?
 

Something strange seems to be going on here.

I'm pointing my EX1 camera at a white wall. Color Balance is set to manual and correctly. Now, when I rotate my $200 circular polarizer by Rodenstock, I get a color shift from light magenta to light cyan passing through white in the middle. What is going on here?

I also tested it with my old Schneider 4x4 pola and got the same effect. I then tested both filters on my PD150 and had NO problems. This a a big problem if you are panning ourdoors as the color shifts are rather dramatic - I've never seen anything like this and was shocked testing it today.

Is there a setting off or something? Can someone explain / fix this? Is this a cmos thing?! I've tried numerous settings both manual and auto white balance on the EX1 and it is still shifting colors.

WHO ELSE IS HAVING THIS PROBLEM?

Could it be the paint on the wall? It's conceivable that some component of the paint is causing different wavelengths to be reflected with different directions of polarization, so your filter isn't cutting all frequencies equally at any given angle and resulting in a color shift away from pure white. I'd try the same thing somewhere else and see if you get the same effect.

EDIT: nevermind, I just noticed that you said you tried it on the pd150 which likely rules out my explanation.

Another possibility would be that there is a degree of polarization in the lens itself - I know I get odd color shifts when I wear polarized sunglasses under a polarized faceshield on my helmet.

Evan, I was shooting outside with blue sky, green tree, and duck ponds with reflections. Turning the pola not only removed the reflections, saturated the colors but really turned everything either to the green or magenta.

Also, if you have to polas and rotate them you can completely eliminate any light. They also make color polas that do neat effects - such as what I am seeing except more extreme.

Im thinking there is some sort of pola / light spliter inside.

I have had inexpensive polarizers that gave a complimentary color shift. I solved that by getting better polarizers. I don't know if that would be a factor in your situation.
Clark

Greg,

Tried to replicatre this inside with my Hoya Pro 1 digital polariser, and couldn't. So far camera behaves normally with a polariser. I will investigate further for you, but can't yet see anything abnormal.

All the best,

Forget wall as paint and light might be bias. Try it on a white computer screen like I see typing this message and make sure your exposure is correct before you judge. Also try it looking through the filter directly without the camera. A good filter will not do this - that is what makes a good polarizing filter good.

My Tiffen linear polarizer exhibits the problem described. However, it's manageable with manual white balance. Panning doesn't seem to have any adverse effects, as long as the camera isn't rolled along its longitudinal axis during the pan.

Panning with a tripod would prevent that from occurring.

Could this be a Linear vs Circular Polarizer thing? IIRC, a standard polarizer is linear, but some cameras needed a circular polarizer for some unspecified reason.

Greg mentioned trying a circular polarizer and got the unwanted color shift.

I think it's because linear polarizers can prevent the auto-focus from working properly.

LETS GET SOME MORE TESTS - PLEASE.

Take camera - include something white in frame. Add Pola and rotate 360 degrees and watch for color shifts in the white (magenta to cyan) (purple to greenish). THIS SHOULD NOT HAPPEN. I'm seeing a 5-15% color shift, I'd guess.

You should see no white changes, rather white reflections of light of objects come and go and the resulting increase or decrease color saturation(brightness/darkness) (not hue shift).

Remember Polas work best at 90% to the sun (not directly into the sun). The sky should darken or lighten but not shift to greenish blue or purplishblue.

When I get my new Mac in a few weeks, I will post pics.

GREAT NEWS - PROBLEM SOLVED - BUT WHY?

Ok, this does not make a lot of sense to me. I've been wondering what I've been doing that could have fixed the camera... Well, I tried the camera this morning with my $200 circular Rodenstock circ. pola and it did NOT WORK - I had my cyan / magenta color shift?! But it did last night? But this morning it was ALSO vinyetting - last night it wasn't... Hmmmm - A CLUE...

Could I have flipped the filter (I do not have my pola screwed in, rather it is sitting in the step down ring of my Chroszeil mattbox. So, I popped it out (which I had done the night before) and flipped it - popped it in... NO COLOR SHIFT AND NO VIGNETTE - SINCE IT SAT A FEW MM CLOSER TO THE LENSE!!

So, I tried it with my Scheinder 4x4 circular pola and it FAILED... both front and back - flush to the lense - (It still works fine on my pd-150). hmmmm. - A MYSTERY.... even after re-color balanced - all manual settings. and camera turned on and off.

Now the Tiffen screw in - WORKED when screwed in and FAILED when flipped and held by hand in front backwards.

SO CONCLUSION - THERE IS A FRONT / BACK TO SOME POLAS. Maybe there is a glare reflecting coating that is effecting the camera when its flipped. Why the Schneider fails both ways - I dont know and that is disturbing as it works on my PD-150.

Anyway - TEST your polas and make sure they are faciing the correct direction.

Thanks everyone - anyone who can tell me why? Chime in - they are all circular polas (no linear polas) and all $150+ dollars.

Greg...

If I recall from when I had a circular polarizer (it broke when it fell out of my camera one day) there is a front and a back to it. It was marked accordingly.

Check to see if it's oriented in the proper direction and give it a try.

You're providing valuable info for others who also need to use polarizers.

Greg,

My Hoya Pro 1 Digital Circular Polariser is clearly marked with correct orientation and does not display any unexpected colour shift under any light conditions. I can't fault it.

Ok,

To answer your concerns and questions and general filter theory:

1) A circular polarizer is a simply a linear polarizer with a 1/4 wave plate retarder installed which confuses beam splitters used in a very limited number of cameras. Virtually all HDV Cameras today (including the EX1) do not need a circular polarizer to function properly.

2) As you discovered, the orientation of a circular polarizer is very important. If you place it in the wrong side it will not polarize the light at all and will simply cause color shift and other problems you were experiencing. A linear polarizer doesn't matter which way you put it on the lens it will work.

3) As far as the Rodenstock working and the others (including ours) is a mystery to me. We own and have thoroughly tested an EX1 with most of our filters and have not had any color shift or other issues. I would love the chance to see some sample images and attempt to trouble shoot this problem with our polarizer on our camera. The only thing that comes to mind is that the EX1 may be more sensitive to IR light and that maybe causing the color shifts you are experiencing.

Ryan Avery
Schneider Optics