Explanation for Inconsistent Sky Color??

[mtimperman]

Does anyone have an explanation for the deep blue streak in the sky in the middle third of this photo? I am pretty sure it has something to do with the polarizing filter, but have never seen anything like this before. It was taken with 10D, 16-35mm F2.8L and 77mm circular polarizing filter. Any comments appreciated. Thanks in advance.

http://web.blueone.net/mike.timperman/CRW_6857_JFR.JPG

[Belmondo]

I've had a similar problem with my 17-40L (shooting at 17mm). It is definitely the CP, and I don't know that there's anything that can be done except to use a little less of the polarizing effect. I've stopped using the CP on that lens because it's hard to predict when the problem is going to happen.

[PacAce]

Are you talking about the gradual color change of the sky from a lighter shade of blue to a darker shade of blue? Yes that will happen with a CP but that can also happen, to a lesser degree, even without the CP.

As for Tom's comment about not using the CP because he can't predict when it happens, my question is why can't you predict it? You should be able to see any effect the CP has on the you image, no? Or am I missing something here?

[Belmondo]

My experiience is that the effect is too subtle to see in the viewfinder clearly enough to anticipate how it's going to affect the final image.

[scottbergerphoto]

I get the same thing periodically with a B+W 77mm CPL and my 16-35 2.8 L. Once I started seeing it in my images, I started paying more attention to the polarizing effect in the viewfinder and backing off a bit when there is too much dark blue. It isn't as easy to see in the smaller viewfinder as it is in a picture until you get used to seeing it.
Scott

[mpkirby]

mtimperman wrote:
Does anyone have an explanation for the deep blue streak in the sky in the middle third of this photo? I am pretty sure it has something to do with the polarizing filter, but have never seen anything like this before. It was taken with 10D, 16-35mm F2.8L and 77mm circular polarizing filter. Any comments appreciated. Thanks in advance.

http://web.blueone.net/mike.timperman/CRW_6857_JFR.JPG


I saw something like that on the 28mm end of my 28-135 with a circular polorizer.

I think you are likely to see this only with wide-angle shots. (Anything zoomed should not have it as much)

Presumably what is happening is the angle at which light is entering the lens is changing as a consequence of the angle of entry.

Any rays coming in straight on, are being blocked 100% The further off-angle the rays come into the lens, the more polarized light is making it past the filter.

Also, make sure you see this on the original un-resized image as well. I had a case where I saw some artifacts on resized versions, but the original seemed much more gradual in its uniformity.

Mike

[slin100]

The effect you see is a well-known consequence of using a polarizer on a wide angle lens. The polarization of skylight varies with the angle of the sky to the sun. It's greatest in the region of the sky that is 90° to the sun. A simple method is to point your index finger at the sun. Your thumb will then point to the region of maximal polarization.

Because the polarization of skylight is not the same everywhere, a wide angle lens is more susceptible to the effect you witnessed.

[Daytripper]

....and the effect is most obvious early in the morning and late in the afternoon....

[DAMphyne]

It seems to me that I read somewhere(?) that the direction of light falling on the sensor can cause degradation of the image. One of the manufacturers was(is) in the process of producing lenses that will direct the light at Right(90degrees) angles to the sensor, thus allowing the light to be spread evenly across.
I'm not sure if this is the issue, haven't heard much about it other than that particular article.
I don't remember that effect with my film camera, although I probably wasn't as critical of the images from film. Anything that seemed strange I could blame on the film stock, processor, or my poor shooting habits.
Just a thought, I've been told, my thinking is what gets me in trouble though.

[slejhamer]

slin100 wrote:
The effect you see is a well-known consequence of using a polarizer on a wide angle lens. The polarization of skylight varies with the angle of the sky to the sun. It's greatest in the region of the sky that is 90° to the sun. A simple method is to point your index finger at the sun. Your thumb will then point to the region of maximal polarization.

Because the polarization of skylight is not the same everywhere, a wide angle lens is more susceptible to the effect you witnessed.


I agree completely; this is a consequence of using a polarizer with a wide angle lens.

That said, I haven't experienced quite so extreme a result as you have posted here. Could be the time of day at which the picture was taken, as Daytripper stated.

[iwatkins]

The shot below is on a Sigma 17-35 (but at 17mm) with a circ po.

You can see that the effect is very prominent. Sometimes it spoils a picture (like here), other times I think it does enhance it.

Cheers

Ian

http://www.netcomuk.co.uk/~iwatkins/gallery/images/1536_1209.jpg

[nosquare2003]

I avoid using polariser on a super wide angle lens (in most situations). However, I've seen some comments that it can be used to create some creative and dramatic pictures. However, I've never seen one. (And certainly, I'm not creative enough...) Any one helps to show it or to provide any guidances? Thanks.