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09-05-2013, 02:05 PM   #1
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Marumi DHG circular polarisa help

I've bought a Marumi DHG circular polariser filter and i'm not sure which position to rotate it to, it's got a little arrow on it and when you rotate it, the arros moves around it. I tried looking through the viewfinder and rotating it and thought the image would be ok, but when I got hom the bottom half of the photo is extremely dark. If I rotate it the image does change in the way of contrast etc..but then the sky doesn't look any different from what I can see to not using the filter. Here's a photo I took ealier using it.



Can you see the sky is ok'ish but the foreground is way too dark, is there any way I can get round this without having to use massive amounts of fill in in Adobe Camera Raw?

09-05-2013, 02:52 PM   #2
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A polariser acts like an ND filter - it'll underexpose the whole scene by 1>2 stops, so you need to increase exposure by 1>2 stops. The whole of your picture is under-exposed which is why it's come out so dark. The position of the arrow has no effect on the exposure, so once you've experimented a bit you'll know to always dial in the same exposure compensation. The rotation of the filter (arrow) only affects how dark the sky gets in the shot.

I notice that the sky is darker on the right. As a general rule, try to ensure that the sun is behind you when using a polariser, that way the effect across the sky should be more even. If you check your LCD after taking a shot with a CP, and you see the sky is dark on one side, turn your camera in the direction of the dark sky (away from the sun) and shoot again. It should even things up. In your case, I would have turned to the right.

Keep in mind that time of the day plays a big role in the amount of polarisation you can get from a polarising filter. You can obtain maximum polarisation when the sun is at about 37 degrees from the horizon, so if the sun is directly overhead or very close to the horizon, the effect of the polariser will vary and in some cases you might not even see any polarisation effect no matter how much you rotate the filter.
09-05-2013, 03:02 PM   #3
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What camera settings did you use when you took the photo? I couldn't extract any EXIF from the image you posted. If you shoot RAW (which I recommend), it will be trivial to adjust exposure in post-processing.

A polarizer will work best pointed 90 degrees away from the light source (the sun in this case). However I'm not sure it's really that necessary for the photo you posted based on the composition, since making the sky a deeper blue could be done with post-processing, and I don't see any objects in the scene that would be prone to a lot of reflections (or need to have reflections enhanced). Here are a couple of articles on how and why to use a polarizer:

How to Use a Circular Polarizer (CPL) | EricLeslie.com

How, When, and Why to Use a Polarizing Filter
09-05-2013, 03:23 PM   #4
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The polarization affect in the sky is greatest when the sun is at right angles to the camera. But that is far from the only use of a CPL. It is also useful in removing glare from glass, water, roads, ... again, the effect is strongest when the glare is coming at right angles to the camera. And as noted - in a pinch you can use it as a neutral density filter to slow shutter speeds and minimize the corresponding affect from stopping down.

09-05-2013, 04:32 PM   #5
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Yeah I forgot to look at which direction the sun was, but I remember reading many times that the sun should really be at about a 90 degree angle to the lens, at least I think it's 90 degrees I read quite a few places anyway.
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