off lens polarizer

Discussion in 'Photography Beginners' Forum' started by tom beard, Sep 28, 2009.

  1. tom beard

    tom beard TPF Noob!

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    I have a P&S with a 31mm lens barrel, and want to shoot polarized photos with it. I took the polarizing filter off one of my SLR lenses which measures 57mm. So, I'll just hold the polarizer in front of the smaller lens barrel. My question is, do I rotate the entire stacked polarizer or should I hold the rear of the filter steady while twisting the front element? I can thread a clear filter to the rear element of the Pola to give me something to hold on to if needed but I figure the fewer surfaces to shoot through, the better. The P&S has little control, ISO and adaptive lighting. I'm assuming that the TTL light meter won't get confused. Any advice gratefully accepted.

    Tom Beard
     
  2. Plato

    Plato TPF Noob!

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    Rotate the entire filter. The rear portion is empty and serves merely to hold the assembly in place while you rotate the glass.

    The TTL metering will work just fine IF the polarizer is a "circular" polarizer.

    More years ago than I'm willing to admit, I did the same thing with a Kodak Brownie and my big brother's polarizing sunglasses.
     
  3. tom beard

    tom beard TPF Noob!

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    Thanks Plato. I didn't know that the rear part of the filter was a blank. Yes, it is circular. As to your Brownie, I guess maybe there really IS no such thing as a new idea. TB
     
  4. Plato

    Plato TPF Noob!

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    You're most welcome.

    The confusion arises because there really are two pieces of glass. However, they are bonded together with the polarizing film and the quarter wave plate (circularizing film) between them. You couldn't get them apart if you wanted to. The sandwich is the "single piece of glass" in the front ring.
     
  5. Dwig

    Dwig TPF Noob!

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    BTW, it is very important that you hold the polarizer facing properly. The same "rear" of the filter, the side with the male threads, must face back toward the camera just the same as it does when mounted on your other camera. If you turn it around it won't work at all.
     
  6. Plato

    Plato TPF Noob!

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    Yes! Thanks for the comment. Actually, it'll work just fine backwards except that the autofocus and the metering will be screwed up.
     
  7. Dwig

    Dwig TPF Noob!

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    No it won't. When light passes the "wrong" way through a circular polarizer it passes through the extra "circular polarizing" element, which effectively depolarizes the light, before passing through the linear polarizing element.
     
  8. Plato

    Plato TPF Noob!

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    You made me think more :scratch: about the situation and you are definitely correct. The polarized light from the reflected surface won't be polarized when it hits the polarizing element. Wow, I'm getting tongue-tied.

    Thanks for pushing the issue.
    :wav:
     

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