Posted by Paul DeCesare on June 28, 2008 at 12:21 AM
In this snapshot of Mt. Garfield it shows a weird thing going on when I use my circular polarizer: depending on where I turn it, I get a dark blob in the sky with brightness of each side (hope this shows in the compressed upload). It seems to happen when I'm zoomed out to 17mm (using a 17-40mm on a Canon 5D). Is this normal behavior for a CPL on super-wide shots? BTW, it's a B+W Kaesemann CPL, so it's not a cheap-filter issue I don't think.
I'm betting the dark spot is due North from your position. Sure looks like the country on I-70 in Utah. If so, I could also guess that you were eastbound.
You often get really dark skies to the north with polas with lighter on either side. It's especially noticeable with wides.
How are my guesses?
Posted by Adam Schallau on June 28, 2008 at 12:45 AM
This is normal behavior for a circular polarizer on a wide or ultra-wide lens, and it's why many photographers avoid using them with lots of sky in the frame. Keep in mind that a polarizing filter will have maximum effect when you have your camera aimed 90 degrees from the sun, and less effect when aimed towards or away from the sun. What you are experiencing here is uneven polarization due to the fact that your lens (set at 17mm) is seeing 104 degrees of the sky and the effect varies from one edge to the other.
Posted by Fred Stearns on June 28, 2008 at 12:54 AM
Paul,
It is a common occurrence. The polarizer works best at 90 degrees from the sun. It falls off as you point closer to the sun or point farther away from the sun. If you follow this reasoning, a wide angle lens takes in a wider section of the sky and you will see that the darkest sky is directly at 90 degrees from the sun and the sky will lighten as the angle gets less or greater than 90 degrees. It doesn't matter whose lens you are using or who made your polarizer. If you turn the polarizer so that it isn't as effective, you can get better results. As with so many things, you can experiment to see how much you can turn the polarizer to get acceptable results. This is likely to be different for every set up. Back in the olden days when I too used to live somewhere East of the Mississippi, I used a polarizer to get some blue into the sky. I do not remember any problems such as you have in this picture. Actually, I don't remember any such problems in southeast and central Texas either. I think it has something to do with the humidity that we don't have out here. Since moving to Colorado, I have quite a collection of pictures with the shade of blue in teh sky looking very much like yours. In the rush of things,I keep forgetting to watch how far I turn the polarizer!
Good luck! And don't forget to enjoy the severe clear skies of the west. You will learn to dream and pray for clouds of any sort to break the monotony!
Posted by Kent Staubus on June 28, 2008 at 12:03 PM
I am a polarizer addict, and ultrawides are my favorite lenses. I see this sort of thing all the time. Sometimes all I can do is switch to using an ND grad filter.
Kent in SD
Posted by Paul DeCesare on June 28, 2008 at 12:55 PM
Hank, your guesses are almost dead on. Everything was correct except the location, but you were CLOSE. I had just left Grand Junction, CO, and I was on I-70 eastbound, but Utah was about 30 minutes behind me. Close enough!
Adama/Fred/Kent, that all makes sense. I didn't even think about the fact that a 17mm is 104 degrees wide, extending past the range of the "90-degrees-from-the-sun" point I was aiming at. This 17-40mm is only months old in my life, so I'm learning these things.
So thanks for confirming that my B+W filter is not defective!
I couldn't decide whether this was the beginning of the Book Cliffs around Green River or the "end" as you enter the canyon headed for Glenwood Springs, but I felt pretty confident it was I-70. The clouds should have been a giveaway.
One thing to try before giving up on the image Paul-
You might be able to "dial out" most of that dark area or tone it down, or conversely "dial up" the light area using Selective Color under Adjustments in Photoshop. After clicking on Selective Color, go to the blue and cyan channels and move the black slider in each. I frequently use those controls to adjust polarizer affects in skies, and if you're lucky on this image, there will be enough difference in the balance of blues and cyans in the sky that you can exploit them for a meaningful correction.
Cool tip, thanks. I have some slides ( ! ) from a trip to AZ/UT that have shocking blue sky gradients. I had a 20 mm lens, Velvia, polarizer foolishly cranked to max..... Some are scanned so I can work on fixing that weirdness.
Lia, I know what you mean, that area is so photogenic between Mt. Garfield, Grand Mesa, and the Colorado National Monument.
Hank, this shot is just to show the CPL effect... the road is showing and a pickup truck speeding by. I pulled over and got some shots where I zoomed in that are worth PP time. I'll post one shortly. BUT, this image may be worth using to practice with getting the sky even.
Discussion
9 repliesAny ideas?
Thanks!
You often get really dark skies to the north with polas with lighter on either side. It's especially noticeable with wides.
How are my guesses?
It is a common occurrence. The polarizer works best at 90 degrees from the sun. It falls off as you point closer to the sun or point farther away from the sun. If you follow this reasoning, a wide angle lens takes in a wider section of the sky and you will see that the darkest sky is directly at 90 degrees from the sun and the sky will lighten as the angle gets less or greater than 90 degrees. It doesn't matter whose lens you are using or who made your polarizer. If you turn the polarizer so that it isn't as effective, you can get better results. As with so many things, you can experiment to see how much you can turn the polarizer to get acceptable results. This is likely to be different for every set up. Back in the olden days when I too used to live somewhere East of the Mississippi, I used a polarizer to get some blue into the sky. I do not remember any problems such as you have in this picture. Actually, I don't remember any such problems in southeast and central Texas either. I think it has something to do with the humidity that we don't have out here. Since moving to Colorado, I have quite a collection of pictures with the shade of blue in teh sky looking very much like yours. In the rush of things,I keep forgetting to watch how far I turn the polarizer!
Good luck! And don't forget to enjoy the severe clear skies of the west. You will learn to dream and pray for clouds of any sort to break the monotony!
Kent in SD
Adama/Fred/Kent, that all makes sense. I didn't even think about the fact that a 17mm is 104 degrees wide, extending past the range of the "90-degrees-from-the-sun" point I was aiming at. This 17-40mm is only months old in my life, so I'm learning these things.
So thanks for confirming that my B+W filter is not defective!
I knew exactly where this was taken, that scene is embedded into my brain. I love that formation.
One thing to try before giving up on the image Paul-
You might be able to "dial out" most of that dark area or tone it down, or conversely "dial up" the light area using Selective Color under Adjustments in Photoshop. After clicking on Selective Color, go to the blue and cyan channels and move the black slider in each. I frequently use those controls to adjust polarizer affects in skies, and if you're lucky on this image, there will be enough difference in the balance of blues and cyans in the sky that you can exploit them for a meaningful correction.
Cool tip, thanks. I have some slides ( ! ) from a trip to AZ/UT that have shocking blue sky gradients. I had a 20 mm lens, Velvia, polarizer foolishly cranked to max..... Some are scanned so I can work on fixing that weirdness.
Pete D.
Pete D.
Hank, this shot is just to show the CPL effect... the road is showing and a pickup truck speeding by. I pulled over and got some shots where I zoomed in that are worth PP time. I'll post one shortly. BUT, this image may be worth using to practice with getting the sky even.