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Thread: Do I need to use exposure compensation with a polarizing filter?

  1. #1

    Question Do I need to use exposure compensation with a polarizing filter?

    Hi everyone and Happy New Year!

    I have a Canon EOS 300D and a polarizing filter I use for reflections and outside in bright light. Do I need to set exposure compensation on my camera (and if so, how much) or does the 300D automatically compensate for the filter in its reading?

    Thanks a lot for your help!!!

  2. #2
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    I believe the compensation will be automatic.

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    Moderator catchlights's Avatar
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    Is it a circular polarizing filter? The camera metering system will compensate the filter factor automatically.

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    No need.


    The camera will auto-meter cos metering is TTL(through the lens)

  5. #5

    Talking

    Thanks for everybody's quick comments!
    Quote Originally Posted by catchlights
    Is it a circular polarizing filter? The camera metering system will compensate the filter factor automatically.
    I'm not quite sure how to determine whether my filter is "circular" or not but it contains two cylinders that move independently of eachother. I rotate the forwardmost cylinder (with the glass) to get the desired effect. Does that clarify at all? (I'm feeling pretty st*pid )
    Last edited by DeltaOmega; 3rd January 2005 at 09:16 PM.

  6. #6

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    Quote Originally Posted by DeltaOmega
    Thanks for everybody's quick comments!

    I'm not quite sure how to determine whether my filter is "circular" or not but it contains two cylinders that move independently of eachother. I rotate the forwardmost cylinder (with the glass) to get the desired effect. Does that clarify at all? (I'm feeling pretty st*pid )
    What you have is a circular polariser, because it turns in a circle.

    I never trust the camera's meter (TTL or whatever) when I use a filter. For a polariser, I give 2 stops more then the metering without the polariser.

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    Moderator catchlights's Avatar
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    The linear and the circular look the same, but you can tell by the words on the ring of the filter, the linear (normal) polarizing filter will just state PL, the circular one will read PL-CIR.

    Hope this help.

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    Quote Originally Posted by catchlights
    The linear and the circular look the same, but you can tell by the words on the ring of the filter, the linear (normal) polarizing filter will just state PL, the circular one will read PL-CIR.

    Hope this help.
    My filter states "PL" so I guess that means it is a linear (as opposed to circular) polarizing filter

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    Senior Member sammy888's Avatar
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    Quote Originally Posted by DeltaOmega
    Thanks for everybody's quick comments!

    I'm not quite sure how to determine whether my filter is "circular" or not but it contains two cylinders that move independently of eachother. I rotate the forwardmost cylinder (with the glass) to get the desired effect. Does that clarify at all? (I'm feeling pretty st*pid )

    BOTH Linear and Circular Polariser are made up of two cylinders that move independently of each other. The only difference is that all those using AF lens on SLRs or DSLRs need to purchase the "Circular" version and not the Linear one as it affect your auto AF. Your AF will just go wild and not focus on your subject. Linear Polariser are the early days version and are meant for non AF manual lens.

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    Sammy, I think my understanding of linear versus circular polariser is likely wrong!

    I realise this may be a useless question as most people would not have a linear polariser these days. But do you know what is the difference that made the linear and circular different?

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    Senior Member sammy888's Avatar
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    Quote Originally Posted by student
    Sammy, I think my understanding of linear versus circular polariser is likely wrong!

    I realise this may be a useless question as most people would not have a linear polariser these days. But do you know what is the difference that made the linear and circular different?
    Well it is pretty true that Linear Polariser are not as common these days. As AF lens have been ramphantly taking over from primes lens the past decade or so.

    Far as I am aware without going into total technicality, it is the way this special filter cuts certain light rays like glares. The way it eliminate the layers also meant it cut away certain light qualities that is important to the way the lens' AF works. I understand it to mean that it can work at one moment when the light is condusive but when you twist the filter's secondary rim on the polariser to optimise the lighting...eg polarising effect, that effect will not just cut off glare but change the way light and image is percept through the lens to lineup the focus with it's AF matrix and thus confuse it. I am one of those who previously has both the Linear and Circular filter when the technology was in the intermeduate stages of overlapping back then.( damn I feel so old sometime thinking about it)

    When the F3AF first made it debut..the AF was not done through the lens but by a device afixed to the camera so Polariser were all linear back then but as AF starts to get more popular they have to address this problem and out came this circular polariser. Far as I can imagine it...the linear is really like "strips" of glass arrange line by line to form the filter surface. Rotating it will shift light in a horizontal manner to effect it ..like the way a prism can break down white light to form the rainbow. But with a circular polariser, this is not arrange in "strips" but in a circular manner so that has some how managed to keep doing the polariser effect but not interfer with AF lens. Also from what I read ..it also depend on the AF technology in terms of brands. Seem ther was more then a fw way of approaching AF technology back then too. I don't have time to check that out but I learn about that in one of my old photography books or magazines long time back. I hope i managed to explain alittle about it...this was how I recalled it.

    I guess why I brought up the linear polariser issue or whoever started this discussion was because, in the market there are still shops or even individual who might be using them and now trying to sell them. If buyers are not aware, they might end up buying the wrong filters if they use solely AF lens. If a polariser is sold too cheap..this could the reason. Polariser last a long time! I have a b+w one for about 11yrs...not a scratch on it all this time. I have already sold off my linear one years ago.
    Last edited by sammy888; 4th January 2005 at 10:52 AM.

  12. #12

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    Thanks!

    As mentioned before, I was not even born (OK! Exaggerating!) when you were doing photography!

    Although I was aware of the existence of linear polariser, it never bothered me as I started right away with the CP. However I am still uncomfortable with metering through a CP, as well as almost any filter! So I make adjustment to exposure manually.

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    Senior Member Pablo's Avatar
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    Hi,

    A circular polariser admits light in a circular or spiral plane.
    This tends to reduce light metering errors with SLR/DSLR's which use a polarising surface
    to seperate and re-direct light to internal light meters and auto-focus sensors.
    Linear polarise filters are for totally manual cameras I believe

    Please correct me if I am wrong, thanks.
    Time, is an effortless construction :)

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    Senior Member sammy888's Avatar
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    Quote Originally Posted by Pablo
    Hi,

    A circular polariser admits light in a circular or spiral plane.
    This tends to reduce light metering errors with SLR/DSLR's which use a polarising surface
    to seperate and re-direct light to internal light meters and auto-focus sensors.
    Linear polarise filters are for totally manual cameras I believe

    Please correct me if I am wrong, thanks.

    You are right on the mark man! heh...

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    Moderator catchlights's Avatar
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    Quote Originally Posted by Pablo
    Hi,

    A circular polariser admits light in a circular or spiral plane.
    This tends to reduce light metering errors with SLR/DSLR's which use a polarising surface
    to seperate and re-direct light to internal light meters and auto-focus sensors.
    Linear polarise filters are for totally manual cameras I believe

    Please correct me if I am wrong, thanks.
    Yes. That's correct.

  16. #16
    Senior Member sammy888's Avatar
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    Quote Originally Posted by student
    Thanks!

    As mentioned before, I was not even born (OK! Exaggerating!) when you were doing photography!

    Although I was aware of the existence of linear polariser, it never bothered me as I started right away with the CP. However I am still uncomfortable with metering through a CP, as well as almost any filter! So I make adjustment to exposure manually.

    Bro...your SLR or DSLR meter's the light "through the lens"(TTL) so that means you dont need to compensate. The only time you do so is if you are using any old SLRs that does not do TTL metering..then you need to compensate for it. Thus if you own one of those older SLRs then reading your polariser's product pamplet or booklet will let you know how much to compensate.

    I think maybe you mistook the darker rich colours for being abit dark heh... In any case, I would rather have the darker colour so I can still lightening it in post production then to have it over exposed

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    Quote Originally Posted by Pablo
    Hi,

    A circular polariser admits light in a circular or spiral plane.
    This tends to reduce light metering errors with SLR/DSLR's which use a polarising surface
    to seperate and re-direct light to internal light meters and auto-focus sensors.
    Linear polarise filters are for totally manual cameras I believe

    Please correct me if I am wrong, thanks.
    Yep, spot on. I believe any camera that splits the light beam for AF and metering functions, be it SLR or P&S, will require a circular polariser.

    Here's a good explanation I picked off the web-->


    "A linear polarizer has a single plate for polarizing the incoming light. When this plate, which is attached to the filter, is rotated, the polarized light will change "phase/angle."

    Some cameras, especially those SLR/DSLR bodies, have a beam-splitter to split the incoming light to the viewfinder, AF system and metering. Each of these components requires some minimal amount of light to work properly. For example, the AF system usually requires an aperture of F5.6 or larger. Thus, this splitting of light should follow a constant ratio, say 80% to viewfinder, 10% to light meter, and 10% to the AF system (just an example).

    If the incoming light is NOT polarized, the phase/angle of the incoming light may be in all directions and evenly distributed to each of the three components. If the incoming light is polarized, depending on the way the incoming light is polarized, the phase/angle of the polarized light may be biased. In other word, since some portion of the incoming light is missing due to polarization, the light diverted to the three components may not be constant. For example, 70% to viewfinder, 5% to light meter, and 8% to the AF system. If the light is polarized significantly, the portion of the incoming polarized light that can reach the AF system may be too low to allow the AF system work properly. Or, if the light that reaches the light meter is lower than the expect level, the meter will "think" the scene illumination is insufficient and force the camera to use a larger aperture and/or a slower shutter speed. As a result, you might get over- or under- exposed images.

    To overcome this problem, a second plate is added to a polarizer to "repolarize" the polarized light. The polarizers that have one plate are the "linear" ones, and the polarizers that have two plates are "circular" ones.

    Therefore, if your camera does not have a beam splitter, you can use linear polarizers. Virtually all consumer level digicams do not beam splitter, and all SLR/DSLR bodies have beam splitters."


    Cheers,

  18. #18

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    Quote Originally Posted by sammy888
    Bro...your SLR or DSLR meter's the light "through the lens"(TTL) so that means you dont need to compensate. The only time you do so is if you are using any old SLRs that does not do TTL metering..then you need to compensate for it. Thus if you own one of those older SLRs then reading your polariser's product pamplet or booklet will let you know how much to compensate.

    I think maybe you mistook the darker rich colours for being abit dark heh... In any case, I would rather have the darker colour so I can still lightening it in post production then to have it over exposed
    Thanks

    My camera do have TTL. But I have developed a shooting "style" where I do not trust the camera's meter. I make more accurate exposures this way.

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    Quote Originally Posted by student
    I never trust the camera's meter (TTL or whatever) when I use a filter. For a polariser, I give 2 stops more then the metering without the polariser.
    and...

    Quote Originally Posted by student
    My camera do have TTL. But I have developed a shooting "style" where I do not trust the camera's meter. I make more accurate exposures this way.
    ...are contradictory. How do you meter then?

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