What is the best polarizing filter for my RZ? Not looking to spend heaps ;)

Discussion in 'Medium Format Cameras and Accessories' started by Holly, Oct 6, 2010.

  1. Holly

    Holly Member

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    Hey everyone

    I just read that the filter I'm using on my RZPro II is apparently specifically made for 'autofocus SLR cameras'.
    It's a Hoya 77m circular polarizing filter.
    So my question is, will there be any difference to my images if I use this filter, or should I use one that is more suitable for my RZ??
    And if so, which ones are the best to use?
    I'm needing one for saturation of skies/foliage greens more than reflection elimination.
    Cheers
     
  2. Q.G.

    Q.G. Inactive

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    A circular polarizer is a regular linear polarizer with a device (called a quarter wave plate) behind it that turns polarized light into 'unpolarized' light again (not really unpolarized, but the plate gives the polarisation vector a twist, sets it into rotation, and the light will behave like unpolarized light.)
    That device is expensive. Hence the extra costs of circular polarizers.
    Some metering devices (be it light meters or autofocus sensors) make use of reflecting surfaces, and polarized light will not work properly. And if your camera or meter is among those who are affected, you will need a circular polarizer. If not, a regular linear polarizer will do.

    The effect however is exactly the same, since the polarizing bit in both types is the same.
     
  3. mrred

    mrred Subscriber

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    I have both, as I use them in combination for a variable ND filter. But the point I want to make is that sometimes I don't check which one I grab and have never had a metering problem with my OM10/20,Kiev88cm TTL,F601,E500,E510 and D200. I do use the Cokin P series, if that would make any difference.

    I have a preference to the linear as I don't have to find the "sweet spot" every time, especially for those grab shots.
     
  4. Q.G.

    Q.G. Inactive

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    For that, it would be easier to have two linear polarizers. Put a circular one in front, and it will not work. So with both types, you will always have to make sure you put them on in the correct order.

    ???
    As polarizers, both types work exactly (!) the same.
    So when you can find a 'sweet spot' with one, you should have no trouble finding it with the other.
     
  5. Holly

    Holly Member

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    So with linear, the polarization is set and you don't have to turn a ring, right?
    Whereas with circular, I have to turn the ring and see through the lens when I've
    found the amount of contrast I want.
    Am I right?
    (Sorry, I have used filters before and am not a dullard, but it is pre-caffeine and I
    am just trying to get my head around this clearly!)
    So why would I bother getting a circular if all I'm going to do is turn it to the
    point of contrast that I would instantly get when attaching a linear?
    That's what you meant, isn't it Mrrd?
     
  6. Q.G.

    Q.G. Inactive

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    No, No.

    With both linear and linear + quarter wave plate (i.e. circular) you have to rotate the filter to find the orientation at which it does what you would want it to do.
    There is no difference at all.
    No difference, because the working bit in both types is exactly the same.
     
  7. CGW

    CGW Member

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    Your 77mm Hoya circular polarizer should be fine. Just make sure the outer ring is threaded to take a Mamiya lens hood.
     
  8. tkamiya

    tkamiya Member

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    Holy cow! 77 METER polarizer? that's a one heck of HUGE filter!!

    Note to self: resist making a smart *ss comment next time... :whistling:
     
  9. MattKing

    MattKing Subscriber

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    The circular polarizers are needed because some camera metering systems* are fooled by the light transmitted by linear polarizers.

    Your RZ67 (or more accurately, none of it's metering options) is not one of those cameras.

    The biggest reason to get a circular polarizer anyways is that it allows you to use the polarizer on any camera that you might have (with the appropriate filter size) without worrying about the issue.

    The biggest reasons not to get one are:

    a) cost; and
    b) if you intend to use polarizers as a Neutral Density filter.

    *As an irrelevant aside, does anyone know whether a linear polarizer is compatible with a Canon Pellix?
     
  10. Holly

    Holly Member

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    Tkamiya, yes, I have an RZ the size of a small aircraft hangar. It's rare. But you get that in Australia.
    Ahem. So anyway, I always just meter completely analogue, I don't have a digital
    camera nearby to cheat with, and I don't own a prism finder so my metering for the
    light while using any kind of polarizer will be all about getting f stop and shutter speed
    right, then applying the right compensation ratio, yeah?
     
  11. CGW

    CGW Member

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    Yup. Your polarizer usually costs you 1.5 stops. Last year I got a Sekonic 558 meter that's almost smart enough to hold down a job. It can be set-up to factor in this compensation thru a second ISO button, giving exposure readings with and without the polarizer.
     
  12. Holly

    Holly Member

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    I had a go with the circ. pol filter on yesterday, with confusing..results?
    I set my light meter up to test out what the exact compensation factor would be,
    so I had it set to give me readings 1.7/stop wider than normal.
    I took two shots in a 10 minute period, right after each other. For the first polaroid
    I had the filter turned so that it was un-polarized-looking (?) through the lens.
    Exposed that one according to the meter's compensated reading, 1/6 @ f22.
    It looked normal enough, sky plain, pretty flat light.
    The second polaroid I turned the filter round so it was showing up the contrast
    through the lens visibly. Exposed that one for 1/6 @ f16 because the light
    was quickly fading and the reading had gone down one stop in the space of
    4 minutes. That second polaroid gave me the sky/cloud contrast you associate
    with polarizers, but the overall exposure looks muddy, and underexposed.
    ? Am I not using it right?
     
  13. MattKing

    MattKing Subscriber

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    Holly:

    You shouldn't meter through a polarizing filter.

    Just take a meter reading without the filter (ideally an incident meter reading), and then apply the fixed filter factor to that reading.

    Generally speaking, the orientation of the filter should not affect the exposure setting you choose, although every once in a while you'll be working with a subject where there is so much glare from the (unfiltered) subject that a reflected light reading will be distorted.
     
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  15. chrism

    chrism Member

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    I have always been under the impression that it was autofocus and not the meter that had problems with linear polarizers, hence the reason older manual focus cameras are fine with the linear variety.
     
  16. MattKing

    MattKing Subscriber

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    It wouldn't surprise me if there are auto-focus systems that are affected by polarizers. My personal knowledge is based on somewhat dated experience - I worked as a camera salesperson in the 1970s and early 1980s. At that (pre-autofocus) time there were some systems whose metering systems required circular polarizers (Canon and Leica SLRs spring to mind, IIRC) while others didn't.

    Since then, I haven't had reason to keep track of the issue, because it never has been an issue with my 35mm equipment (Olympus OM - no autofocus) and my medium format equipment isn't autofocus and, with the exception of one metering finder, is also without meters.
     
  17. Holly

    Holly Member

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    Maybe I didn't explain that right..I was using a separate handheld light meter?
    Which I had set up to calculate the filter compensation in-meter for me.
     
  18. Q.G.

    Q.G. Inactive

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    You may have run into why polarizers are generally not a good thing.


    First (and this is not the bad thing about polarizers), polarizers have an overall darkening effect, because they cut out half of the light (at least - more depending on the material used in the polarizer). They do that always, no matter which way the polarizer is rotated. This is your fixed filter factor.

    Secondly (also not quite the bad thing, but already part of it), polarizers darken bits selectively. That's why you use them.
    That can however already lead to images appearing too dark, depending on how big the part of the scene is that is affected by the polarizer. The fixed filter factor (of course) does not compensate for the selective darkening effect of the polarizer. But (in a worse case scenario) your entire scene is affected by the filter... If you do not like that, use less polarizer.

    Thirdly (another part of the bad thing about polarizers), polarizers can remove reflections. That includes specular highlights in your scene. And there are very many of those in outdoor shots. The result (even if the overall appearance of the resulting image is not too dark) is a dull, flat looking image.

    Combined, the effect of a polarizer can be quite horrible.
    And it is easily mistaken for underexposure. That, because it is, but selective underexposure. You elected to do that, and it is not (!) fixed by exposing more, but by using less polarizer.

    So only use a polarizer when absolutely necessary.
    If you should think it is necessary quite often, use your head and eyes, and don't just go for maximum effect.
    If you go for maximum effect anyway, look at what that does to parts of the scene you did not pick the polarizer for (it's o.k. to want to darken the sky, but what does that do to leaves, grass, etc.?) You may then want to rethink what you want to do to the sky.
     
  19. Holly

    Holly Member

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    The result (even if the overall appearance of the resulting image is not too dark) is a dull, flat looking image.
     
  20. Holly

    Holly Member

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    PS. quote thing is not my friend today, sorry. ^
     
  21. Bob-D659

    Bob-D659 Member

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    1.7 stops would be the minimum exposure change for your filter. Depending on how you rotate it and the scene it could easily drop the light another 3 stops or more. All depends on the polarization of the light before it tries to pass thru the filter. This is where ttl metering really helps. There are some very good pol filters made where the extinction of crossed pol filters is nearly 100% of visible light, but they are not usually sold for general photography. The effectiveness of pol filters for general photography vary quite a bit, the usual indication of effectiveness is the brand and retail price.

    Metering with an external reflected or incident meter just isn't going to work very well. You could get a second filter and mount it in front of a reflected light meter and set the rotation angle to match the one on your camera, but it is a pain and you would really need matching filters with degree markings on the perimeter for it to work very well.

    End of ramble. :smile:
     
  22. CGW

    CGW Member

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    What? 3+stops? No. Why is there consensus that between 1.3-1.7 is the standard filter factor for circular polarizers? TTL metering automatically compensates and it ain't 3 stops or more. Dialing in 1.3-1.7 stops more exposure on a incident meter works for me, too. If you couple two polarizers together, it is possible to get a variable ND filter effect by rotating one. Not sure what you're advising makes much sense practically.

    The OP should probably do some research on how polarizers work.
     
  23. Q.G.

    Q.G. Inactive

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    You don't want to meter through the filter, and also catch the effect of the filter.
    The filter is used to block light. Selectively.
    If you don't want the parts that get darker as a result to get darker, don't use that filter.

    So only use the fixed filter factor of the polarizer. The one that compensates for the overall, non-selective blocking of light.
    So no TTL, through-the-filter metering to include the effect of the filter. If you think that the polarizer makes things look too dark, ask yourself: why are you using that filter?
     
  24. Bob-D659

    Bob-D659 Member

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    Some scenes, esp backlit ones, can have a huge amount of polarized light from glare off of objects when the sun is close to the horizon. You can't easily use an incident meter, and the glare makes the reflected meter think the scene is much brighter than reality. Somewhat similar to taking photos in bright sun with lots of fresh snow where you meter and overexpose by a couple of stops. Rotating the pol filter for max extinction completely changes the lighting balance compared to the neutral density type light loss at minimum extinction. As you found this can give you somewhat underexposed negatives, all depends on what you are shooting.

    Try metering a similar scene thru your pol filter with various angles of rotation from minimum to maximum extinction. I think you will see some major changes in the expose the meter calculates.

    As an example, using a pol filter to remove the glare from the surface of a pond so you can photograph the bottom, you can't use incident metering as there can be substantial light loss from the light traveling thru the water in both directions. Besides, most incident light meters are rated as waterproof. :smile: Your only real option in this situation is ttl metering after adjusting the pol filter to remove the glare from the surface, metering thru the filter will be close, but it is awkward to do at best.
     
  25. CGW

    CGW Member

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    "Try metering a similar scene thru your pol filter with various angles of rotation from minimum to maximum extinction. I think you will see some major changes in the expose the meter calculates."

    C'mon, 1.5-1.7 stops isn't exactly "major." Not sure what you're doing to necessitate a +3 stop exp. compensation with a circular polarizer.
     
  26. fschifano

    fschifano Member

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    It's really simple. When you meter through the lens with a polarizing filter, the readings will change as you rotate the filter. However this is just the meter being fooled by the polarizer. Don't go by that. Filter factors for a polarizing filter are usually 1.3 to 1.7 stops. I use 1.5 stops and I'm happy with that. Take your meter reading without the polarizer (or use a hand held meter) and add 1.5 stops more exposure. That's all you need to know, and it works every time. The amount of polarization you dial in doesn't matter. The filter factor is constant. To the OP, since you already have a circular polarizer, you can use it with anything and it works exactly the same as a linear polarizer.