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Thread: polarisers

  1. #21

    Default Re: polarisers

    Quote Originally Posted by Michael View Post
    with pola on, cause in any case you loose about 2 exposure steps...
    so is polar=ND filters?
    (i know they are DIFFERENT.but can a polar act LIKE a ND considering 2 stops loss?)

  2. #22

    Default Re: polarisers

    I'm using the Nikon CPLII, works very well for me up till now... somehow, i dun really fancy shooting with the hood on... even for my 17-35... hehe... lazy man...

    As for shooting at 90deg from the sun.... i think composition is most impt... you can't always get it 90deg from the sun i guess... but if you turn the front dial once you have composed, you would probably be able to get to the "sweet spot" where the sky looks the bluest or there is the least amount of reflection in the window/water...

    just my $0.02... hope that it helps...

  3. #23

    Default Re: polarisers

    Quote Originally Posted by jeanie View Post
    so is polar=ND filters?
    (i know they are DIFFERENT.but can a polar act LIKE a ND considering 2 stops loss?)
    yes, you got that right, at certain angles (for example with the sun in your back, or straight into the sun) the pola acts like a ND.
    The big difference between and ND and pola is that a ND removes light equally over the whole light spectrum and regardless of direction, the pola removes light with certain wave direction...
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  4. #24
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    Default Re: polarisers

    Also you cannot use a Pola in a panorama sequence. You can with an ND.

  5. #25

    Default Re: polarisers

    Quote Originally Posted by jeanie View Post
    you know me.i want the full details.i dun wan to learn 1/2 1/2 bucket of water.

    so HOW do i measure 90degrees?
    ok because its you, your thumb and index finger actually form a 90 degree angle when stretched out. so point the index to the sun, and look where you thumb is pointing too.... and if you are observant you would say now that the thumb can point in different direction depending on how you twist your arm or wrist... correct, the 90deg apply to a circle or plane 90deg to the sun's direction.... got it or do you need a practical session?
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  6. #26

    Default Re: polarisers

    Quote Originally Posted by Blu-By-U View Post
    Also you cannot use a Pola in a panorama sequence. You can with an ND.
    actually you got to be careful even with wide angle lenses that cover more than 90deg....
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  7. #27
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    Default Re: polarisers

    Quote Originally Posted by glensky View Post
    hav commercial plugin 4 that.
    Are you sure?

    Maybe its a gimmick plugin to make sky more blue like polarizer effect. But what happen if you use polarizer to reduce reflection? For example to make green color of leaf come out behind the white reflection. What behind reflection can not be create naturally by any software.

    Regards,
    Arto.

  8. #28
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    Default Re: polarisers

    Quote Originally Posted by Michael View Post
    actually you got to be careful even with wide angle lenses that cover more than 90deg....
    Can explain more?

    Regards,
    Arto.

  9. #29

    Default Re: polarisers

    Quote Originally Posted by Artosoft View Post
    Can explain more?

    Regards,
    Arto.
    as mentioned above, the polarization effect is biggest when pointing the camera at 90deg to the sun. So lets assume the following example: you have a lense that covers 180deg (a fisheye), you point the camera/lense at 90deg to the sun, then the edges of the opening angle covered by the lense will be in direction of the sun and directly away from it respectively. So the centre part of you pic will have max. polarization effect and the edges will have none at all... so if you have a blue sky then it would be dark blue in the centre and light blue at the fringes of the photo.... some may like it some not....
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  10. #30
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    Default Re: polarisers

    Quote Originally Posted by zac08 View Post
    Well, then.... pray tell... how do you replicate the effects of a CP-L when you're shooting at surfaces of water and trying to capture the fishes just under the surface without the CP-L and using CS...
    I think you have to use photoshop and the use the plugin (pictures of fish in your case) and then superimpose under the existing picture.

  11. #31
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    Default Re: polarisers

    Quote Originally Posted by MDZ2 View Post
    I think you have to use photoshop and the use the plugin (pictures of fish in your case) and then superimpose under the existing picture.
    Do show me a photo when you have done so... frankly I dun think it's possible to replicate the same thing at ALL.

    Michael Lim
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  12. #32
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    Default Re: polarisers

    Quote Originally Posted by jeanie View Post
    you know me.i want the full details.i dun wan to learn 1/2 1/2 bucket of water.

    so HOW do i measure 90degrees?
    Even if you don't know the technicalities behind the polariser, you can still obtain the best results for whatever compostion by trusting your own eyes. Just turn the polariser ring until the image reaches maximum saturation. If you start relying purely on technical knowledge, you will end up compromising a better composition just to gain maximum polarisation.

  13. #33
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    Default Re: polarisers

    Quote Originally Posted by zac08 View Post
    Do show me a photo when you have done so... frankly I dun think it's possible to replicate the same thing at ALL.

    I hope you realise that that was only a joke.

  14. #34
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    Default Re: polarisers

    Quote Originally Posted by jeanie View Post
    you know me.i want the full details.i dun wan to learn 1/2 1/2 bucket of water.

    so HOW do i measure 90degrees?


    A polariser simply filters out light that has been 'polarised', which simply means the direction of travel is at a normal of the transmitted electrical energy at a certain angle. This is abit complicated due to physics.

    Namely, to make it simpler, any reflected light is polarised. What a polarisers does is to cut out the reflected light, and its effect is strongest at 90 degrees to the filters polarisation axis (think of a line perpendicular to the surface of the filter. That is why the edges of the frame on a polariser appear darker or 'vignette's compared to the center of the picture, especially if pointed towards the sun.
    By pointing the axis 90 degrees to the source of the light, you get the greatest intensity of polarised light entering your filter, hence the 'higher' saturation of the colour.

    All in all, don't bother about the angle, and yes measure WITH the polariser on. As ortega said, just adjust the polariser ring (circular polariser) which will control the 'darkness' of the picture.
    Last edited by Wisp; 15th December 2006 at 10:17 AM.

  15. #35

    Default Re: polarisers

    thanks all.i'll try.

    but for now...got to go dig up my polar from somethere in the house.

  16. #36
    Senior Member jnet6's Avatar
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    Default Re: polarisers

    Quote Originally Posted by Michael View Post
    with pola on, cause in any case you loose about 2 exposure steps...
    For Nikon CPLII will lose 1.5 stops exactly...

    If you ask me how do i got this value???
    i say is from my camera.

  17. #37
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    Default Re: polarisers

    Quote Originally Posted by jnet6 View Post
    For Nikon CPLII will lose 1.5 stops exactly...

    If you ask me how do i got this value???
    i say is from my camera.
    Usually the polarizer come with small manual that will tell you the lose light number in stops. Does it come with Nikon CPLII? If yes, how much Nikon put there?

    Regards,
    Arto.

  18. #38
    Senior Member erictan8888's Avatar
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    Default Re: polarisers

    the first thing about cir polariser ater you have bought it is to know how to get the DAM* thing out of the lense after it is fixed on !!!

    that is one BIG thing to learn....
    i can never get it off easily once it is on the lens..... xian....
    Hope to learn from everyone here....

  19. #39

    Default Re: polarisers

    a lot of smoke here...let me try to clear the air some with the short version of the story:

    - Light from the environment is un-polarized, ie. the light waves "vibrate" in any direction perpendicular to its direction of travel.
    - Light reflected by a non-metallic surface is polarized.
    - Light is dispersed and polarized by dust and water in the air.

    - Polarizing filter allows only light polarized in a certain "direction" to pass through it.
    - The selection of this direction is by rotating the front disk of the filter.
    - Thus, light passing through a polarizing filter is polarized and only "vibrates" in a certain direction as selected by the user.

    - Polarizing filter makes the sky bluer by a) reducing the amount of light from the sky by only allowing light "vibrating" in a certain "direction" to pass through it (thus reducing the exposure), and by b) reducing the light scattered by reflecting off dust and water in the air (which is polarized by its reflection).

    - Polarizing filter reduces reflections by blocking the polarized light from a reflection from passing through the filter.
    - As only light of a certain direction is allowed through the filter, the user can rotate the filter such that light as polarized to a certain "direction" by the reflection is blocked by the filter and thus cannot pass through and form an image.
    - Reflections off a metallic surface cannot be filtered this way as light is not polarized by reflecting off a metallic surface.

    - There are 2 kinds of polarizing filters: linear and circular.
    - Linear polarizing filter cannot be used with auto metering and auto focusing cameras.
    - Circular polarizing filter can be used with auto metering and auto focusing cameras.

    The long version follows...
    Last edited by theRBK; 16th December 2006 at 09:50 AM.

  20. #40

    Default Re: polarisers

    the long version, for the "full bucket" advocates :

    Light from the Sun comes to the Earth unpolarized. This means that the light waves travelling in a line from the Sun to the Earth have their wave patterns in any direction perpendicular to its travel (in other words, they are like some 3rd world militia marching all out of step, not like a North Korean parade). When light is reflected off a non-metallic reflective surface, it is polarized to a certain extent by this process of reflection (note: don't try to remove the reflection on a metallic surface, including mirrors...after awhile, you begin to look pretty foolish). Thus when it hits the atmosphere, the light is reflected every this way and that by dust and water in the atmosphere (everything even more garang gabo). The amount of polarization depends on the angle of the light hitting the reflecting surface. So, a significant part of the light hitting the lens is a jumbled mess of unpolarized light.

    When we are talking about making the sky bluer with a polarizer, what we are doing is actually cutting out some of the light from the sky so that the effective exposure from the sky is less. Also, the light reflected off dust particles will as well be reduced. The polarizer does this by selectively allowing through the filter light that is only "vibrating" in one "direction". This "direction" is selected by rotating the front disk of the polarizing filter. But the effectiveness of the blueing of the sky also depends on the angle of the light Sun relative to the lens. As above mentioned, the effective polarization from reflection depends on the angle of the light hitting the reflecting surface. Thus, from experience, for effective blueing of the sky, it is optimal if the Sun is 90 degrees from the plane at which light enters the lens.

    When we talk about removing reflections, what we are talking about is blocking the light polarized by the reflection in a certain "direction". So, by turning the front disk of the filter in a certain direction, light as polarized by the reflection is filtered away, thus removing the appearance of the reflection.

    So, if that's the case, how come some things don't totally disappear cause what we see in this world is all reflected light? Because, as mentioned above, some of the unpolarized light is unpolarized by the reflection process. As well, what we normally consider "non-reflective" surfaces actually reflect light in a mess of "directions" and some of that light will be admitted in. But as a result of this filteration, less light is admitted to the lens. This is why a polarizing filter acts in a way as a density filter. But this effect is not uniform, and so it is only a rough estimate that light reduced is about 1.5 to 2 stops. That's why it is good to meter through the filter.

    There are 2 types of polarizing filters: the linear and the circular. This does not describe their shape or the light they filter away. Photographically, they produce the same effect. But the linear polarizer should not be used with "through the lens" (ttl) metering or auto focus. A linear polarizer filters away light polarized in a certain direction and that's it. Ttl metering and auto focus systems are fed with light through a beam splitter, and if the "direction" of the light does not allow or reduces the amount of light picked up by the splitter, your metering and AF would be off. The circular polarizer on the other hand not only does what the linear polarizer does, it also has a special scrambler plate that mixes the light back again so that the light is more or less distributed evenly in its "direction" (ie. it de-polarizes the light!). This secondary process would allow the ttl metering and AF to work optimally.

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