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Tim Kuang Offline Image Upload: Off Registered: Dec 09, 2006 Total Posts: 15 Country: Canada Polarizer Usage Question Hi everybody, When using a polarizer, sometimes I noticed that the middle is darker while the two sides are lighter (shown in a picture below). I know that when the axis of the lens is not 90 degrees to the sun, I could get uneven polarizing, with one side darker the other side lighter. But what is the reason for the darkness in the middle? Thanks a lot. --Tim K. May 01, 2007 at 02:48 AM

phil hawkins Offline Image Upload: On Registered: Apr 25, 2006 Total Posts: 1804 Country: United States Re: Polarizer Usage Question It has to do with the angle at which the light hits the lens. There's nothing you can do about it except use telephoto lenses. The wider angle you use the more pronounced the effect. I think Sing-Ray has a polarizer that minimizes the effect, but it's way expensive. Great shot there, by the way... I don't even notice the uneven color of the sky. Phil May 01, 2007 at 03:01 AM

manzico Offline Image Upload: Off Registered: Jun 08, 2005 Total Posts: 198 Country: United States Re: Polarizer Usage Question It has to do with the angles as you stated, but it is a little more subtle. You see polarizers have their greatest effect 90 degrees from the sun so if the sun is on the eastern horizon, the area of greatest effect (darkest blue in the sky for example) will be along an arc from the northern horizon continuing overhead to the southern horizon. The further you get from this 90 degree band, the less of an effect your polarizer will have. If you are shooting with a wide angle lens (usually greater than 24-27mm on a 35mm SLR) the field of view is actually wide enough to see the band and the fall off as your field of view includes parts of the sky significantly far away (30 degrees or more) from the 90 degree band. With a narrower field of view (longer focal length), the effect of the polarizer will be more or less flat across the frame and you won't notice the band. Dave May 01, 2007 at 03:02 AM

Zeph Offline Image Upload: On Registered: Jan 30, 2005 Total Posts: 2564 Country: United States Re: Polarizer Usage Question Great question / Great answer(s) well said! May 01, 2007 at 03:13 AM

Tim Kuang Offline Image Upload: Off Registered: Dec 09, 2006 Total Posts: 15 Country: Canada Re: Polarizer Usage Question Thank you Phil and Dave. I was using my Canon EF 17-40 f4L lens for the photo(I believe it was at the 17mm end, equivalent to 27.2mm's AOV on my Canon digital rebel xt). Does that mean that if I am using a wide angle lens and am 90 degrees to the sun, it will ALWAYS have more polarizing in the middle because the AOV is too wide? I think I will do some experiments to see starting from what focal length this effect is eliminated. Thanks again. --Tim K. May 01, 2007 at 03:17 AM

raceves Offline Image Upload: Off Registered: May 20, 2005 Total Posts: 309 Country: United States Re: Polarizer Usage Question Tim Kuang wrote: Thank you Phil and Dave. I was using my Canon EF 17-40 f4L lens for the photo(I believe it was at the 17mm end, equivalent to 27.2mm's AOV on my Canon digital rebel xt). Does that mean that if I am using a wide angle lens and am 90 degrees to the sun, it will ALWAYS have more polarizing in the middle because the AOV is too wide? I think I will do some experiments to see starting from what focal length this effect is eliminated. Thanks again. --Tim K. Yeah you'll always get that effect at the wide end. It's even more noticeable on my 10-22mm. May 01, 2007 at 03:53 AM

Allen_Maestas Offline Image Upload: Off Registered: Feb 18, 2005 Total Posts: 18502 Country: United States Re: Polarizer Usage Question Wide Angle and high elevation, both together it can be really bad. Just spin that sucker until you get it to even out even if the polarization is minimal it's still better than not having it on there. PS, don't try to use it while shooting panos :) Al May 01, 2007 at 03:57 AM

charlesk Offline Image Upload: On Registered: Oct 21, 2003 Total Posts: 5219 Country: United States Re: Polarizer Usage Question As others said, it is natural, depending on the angle of the shot with respect to the sun. See this issue especially with panoramas, as Al said, but I don't let that stop me. The shadow/highlight tool and other PS gimmicks can greatly reduce this effect; I can show you an example if you like. --c May 01, 2007 at 04:03 AM

Tim Kuang Offline Image Upload: Off Registered: Dec 09, 2006 Total Posts: 15 Country: Canada Re: Polarizer Usage Question Hi folks, After some further thoughts, I found I still have some questions. I noticed that with my Canon ef 17-40 f4L lens, I sometimes get uneven polarization, sometimes I don't. It is this lack of predictability with my wide angle lens that frastruates me from time to time . In my impression, the uneveness in the middle seems to be related to the elevation of the sun: all my photos having uneveness in the middle seem to have the sun in the low horizon and I was 90 degrees to the sun. Since I really like Dave's polarizing band explanation, I am going to use that. Is it possible that the width of the band is changing depending on some conditions, say the elevation of the sun, or the atmosphere, or even the angle to the sun? When the width of the band is small compared to the AOV, it is easy to see unevenness either in the middle or on the side depending on your angle to the sun. Any ideas? Thanks, --Tim K. ps Charles, I would love to see your images if you have time (probably together with a short description how you corrected them :)). I have been using Gradients to correct the problem, but like to know more tricks. Thanks. pps. Al, unfortunately with the small viewfinder on my Digital Rebel xt, it is not easy to tell the polarizing effects. May 01, 2007 at 06:38 PM

mark70x70 Offline Image Upload: On Registered: Aug 01, 2005 Total Posts: 3172 Country: United States Re: Polarizer Usage Question phil hawkins wrote:There's nothing you can do about it except use telephoto lenses.Phil That or "fixing" it in PS with some crafty masking. :) Mark May 01, 2007 at 07:15 PM

Allen_Maestas Offline Image Upload: Off Registered: Feb 18, 2005 Total Posts: 18502 Country: United States Re: Polarizer Usage Question Tim Kuang wrote: Hi folks, pps. Al, unfortunately with the small viewfinder on my Digital Rebel xt, it is not easy to tell the polarizing effects. You'll get used to it and be able to see it better as you get experience. In fact as you get better you'll be able to use it to your advantage in many compositions. Banding is not always a bad thing, many a great landscape photographer have used the polarization banding to their advantage. Good Luck! Al May 01, 2007 at 09:49 PM

charlesk Offline Image Upload: On Registered: Oct 21, 2003 Total Posts: 5219 Country: United States Re: Polarizer Usage Question Here's a quickie I did actually using a technique different from my usual (which is shadow/highlight). Here I actually did a color replacement (Image -> Adjustments -> Replace Color). I selected roughly in the middle of the blue gradient, then adjusted the sensitivity, and increased lightness of the darker blues. Then gave it a slight levels adjustment to increase overall contrast. The sky and water ar every noisy because the original is heavily JPG compressed, so you can obviously do better with the original. BTW, I normally wouldn't "depolarize" to this extent.. I like the deep blue and a bit of gradient doesn't bother me.. this is just to show you what is possible. --c May 01, 2007 at 10:39 PM

Monito Offline Image Upload: Off Registered: Jan 28, 2005 Total Posts: 5658 Country: United States Re: Polarizer Usage Question Yes please, would like to see an example. Please put a link here to the example, so others and myself will be alerted if you post it. Thanks! May 03, 2007 at 11:50 AM

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