Polarizing filter

I purchased a Hoya Alpha Polarizing filter. I am using it on my Nikon 18-70mm on my D7100. When I put it on it darkens slightly, but I do not notice a difference when I rotate it. I know it works best 90 degrees from the sun. Am I doing something wrong? How can I test it? Please help
Thanks.

You should be able to see a difference, especially when looking to the sky with clouds. The sky will transform to vivid blues and darker clouds, etc. Are you using it when the sun is low in the sky. That seems to be when I notice the changes most. Another test is to look at a TV show. Rotate the filter and the picture will disappear. I found that little tip when taking pictures of the g'kids who didn't want to turn off the TV and I didn't want the TV picture in my photo. Ha!

A polarizor only works on light that is polarized. If it isn't the CPL merely acts as a neutral density filter.

480sparky said:

A polarizor only works on light that is polarized. If it isn't the CPL merely acts as a neutral density filter.

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I missed the point that he just stated a polarizer filter and assumed he was talking about a CPL because he stated he rotated it. I guess the rotation could be screwing it tighter and looser to the mount.

cwgrizz said:

I missed the point that he just stated a polarizer filter and assumed he was talking about a CPL because he stated he rotated it. I guess the rotation could be screwing it tighter and looser to the mount.

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CPL are polarizers. And all polarizers, linear or circular, will rotate within the mount itself. Neither will rely on turning the filter on the threads.

Either way, they only work on light that reaches the lens polarized. This is usually accomplished by reflection, refraction or by passing through a polarizing medium.

480sparky said:

CPL are polarizers. And all polarizers, linear or circular, will rotate within the mount itself. Neither will rely on turning the filter on the threads.

Either way, they only work on light that reaches the lens polarized. This is usually accomplished by reflection, refraction or by passing through a polarizing medium.

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Thanks, I was not aware of the fact that a linear polarizing filter did turn. I was only familiar with the C-PL.

If you research your filter online, you should find a filter factor for it. Some CPL filters cut down the amount of light reaching the sensor by 1 to 1.5 stops. Others might cut it by 1.5 to 2 stops. The camera's meter will compensate by changing either the ISO, shutter speed, or aperture when the filter is mounted so you won't really notice much, if any, difference when the filter is mounted on the lens.

When you rotate the filter on the lens, the entire scene won't be affected by the CPL filter. Only the surfaces that are affected by polarized light will be visible to those changes. Keep notice of the sky, reflections in water, reflections on glass windows, and the color of the grass and/or leaves in your scene. Those should change slightly in color or appearance providing you are standing in the correct direction in relation to the sun. If you aren't standing and aiming the CPL in the correction direction to the sun, you won't notice any changes when you rotate the filter.

nikonpup said:

i have 2 hoya nxt cir-pl filters, they have a small white triangle on the rim, when the sun is to your left the triangle is on the right side of the lens and visa versa when the sun is to your right.

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Where did you find that info? I'm asking because I have the Hoya HRT C-PL filters and tried to find some info like that. I even ask in a thread on here someplace where someone said the usually set theirs to 1/4 or so, which didn't make sense to me. Actually, I never paid attention to the white triangle, I just turned it until I liked what I saw. Thanks

Ok I tried the triangle trick and it worked kind of. It did give me darker skies, I was hoping for a little bit more than what it did. At least now I know how to use it, I will use it for a while and if it does not meet my conditions I will look for another a circular polarizing filter.any sugestions.

cwgrizz said:

where did you find that info? I'm asking because i have the hoya hrt c-pl filters and tried to find some info like that. I even ask in a thread on here someplace where someone said the usually set theirs to 1/4 or so, which didn't make sense to me. Actually, i never paid attention to the white triangle, i just turned it until i liked what i saw. Thanks

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old eyes and observation. Blue sky works best but on a lot of shots i do not have that option and spinning the wheel just pissed me off. c. Hand - take lots of shots, practice practice. Your photos will love u for it.

C. Hand said:

Ok I tried the triangle trick and it worked kind of. It did give me darker skies, I was hoping for a little bit more than what it did. At least now I know how to use it, I will use it for a while and if it does not meet my conditions I will look for another a circular polarizing filter.any sugestions.

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If you don't know how to adjust one brand of CPL for maximum effectiveness, switching to another brand will be an exercise in frustration.

Yes that is why I said a few weeks, I want to take photos at different times of day, Different situations and research. I know that I can not judge something like this in 10 - 20 pictures, I understand time and hundreds of photos!

I understand that.

But if you're not using your current CPL to the best of it's ability, how will buying another brand and still not knowing how to use it help you?

Oh I agree, so I did some playing last night. The 90 degree from the sun rule was best and the arrow away from the sun did yield the best results. I will experiment more this weekend. I will go to the Lake and shoot. The interesting thing was that in certain situations it moved the dark corner of the photo from one corner to the other. I was using my Nikon 18-70mm on about 60mm F8 on my D7100.