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Thread: CPL for ND purposes?

  1. #1

    Default CPL for ND purposes?

    Hi I'm a relative noob. Hoping to get a filter to let me take those pix of 'silky' waterfalls, and 'dreamy, smoky' water surfaces. I know ND will be the one that does the trick. However some websites and pp I've spoke to claims that CPL can duplicate the effect to a certain extent, while some say that's BS. May I seek some expert's opinions here pls? :-)

    Anyone have personally used CPL for ND effects?
    What are the stops reduction for CPL, if any?
    Which brand/coating of CPL would be best for this?

    Hoping to save some costs and just get a CPL for multi-puposes at the moment. Then maybe a dedicated ND filter with more stop reduction in the future. What do u guys think?

    Cheers! :-)

  2. #2
    Senior Member giantcanopy's Avatar
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    Default Re: CPL for ND purposes?

    A CPL will cut down an amount of light entering like an ND ( on top of polarising )
    The amount reduced is not uniform across all the brands. Some expensive polarisers cut less / some cut down more. But it might hover around 2-2.5 stops. ( less than what you can potentialy reduce with the ND filters, especially if you need to cut down alot of light )

    The more expensive polarisers are supposed to use better glass and materials / coatings, or slimer mount to reduce chance of vignetting especially on wider angle lenses. Examples include B+W which is pretty popular on this forum. As to whether you really want to spend so much on a polariser is pretty up to the user. Some are perfectly happy with the budget ones.

    Ryan
    Last edited by giantcanopy; 11th January 2009 at 08:49 AM.

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    Moderator nightwolf75's Avatar
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    Default Re: CPL for ND purposes?

    CPL does cut down the amount of light going thru. but AFAIK, it is not enuf to really give you the milky water effect. wat CPL is good tho (apart from giving you the blue skies) is to cut down on the reflections from the water.

    also, ND filters come in different grades depending on how many stops of light it cuts. off the shelf, i think the best we can get from CP is the hoya ND8 (?). on ebay, you can get those really exotic ND400.
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    Default Re: CPL for ND purposes?

    Actually if you have access to the place almost daily, just go during not so bright day. Or come near sunset or just after sunrise. There isn't a lot of light so automatically shutter can be longer. Also you can play with smaller apperture. All you need is to set it at lowest possible ISO and for whatever setting you do, you need 1 sec shutter speed to get the silky water.

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    Senior Member Anson's Avatar
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    Default Re: CPL for ND purposes?

    Quote Originally Posted by giantcanopy View Post
    The more expensive polarisers are supposed to use better glass and materials / coatings, or slimer mount to reduce chance of vignetting especially on wider angle lenses. Examples include B+W which is pretty popular on this forum. As to whether you really want to spend so much on a polariser is pretty up to the user. Some are perfectly happy with the budget ones.
    May I ask does an expensive CP & a budget CP different in IQ so much? Coz even Hoya have different type of CP (same thread size).

  6. #6

    Default Re: CPL for ND purposes?

    Quote Originally Posted by Anson View Post
    May I ask does an expensive CP & a budget CP different in IQ so much? Coz even Hoya have different type of CP (same thread size).
    Good qn :-) I'm wondering the same thing too. I believe B+W is indeed better, but how much better? Would it be noticable to a noob like me? :P But having said tat I rather buy a good one now.. than having to 'upgrade' later.

    Thanks everyone for the advices. Looks like I may get both filters :-D

  7. #7

    Default Re: CPL for ND purposes?

    Quote Originally Posted by vee5 View Post
    Good qn :-) I'm wondering the same thing too. I believe B+W is indeed better, but how much better? Would it be noticable to a noob like me? :P But having said tat I rather buy a good one now.. than having to 'upgrade' later.

    Thanks everyone for the advices. Looks like I may get both filters :-D
    yeah thats wat i think so too when im thinking of getting it. BBB filter

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    Default Re: CPL for ND purposes?

    Most CPL acts like a ND2 filter.. It cut light by 2 stops.. Ken Rockwell uses polariser as its also acts like ND2.. thats what I read from his website..
    Regards

  9. #9

    Default Re: CPL for ND purposes?

    Quote Originally Posted by vee5 View Post

    Hoping to save some costs and just get a CPL for multi-puposes at the moment. Then maybe a dedicated ND filter with more stop reduction in the future. What do u guys think?

    Cheers! :-)
    you might get some unwanted effects from cpl that do not cater to your purpose of nd filters.

    and most cpl might not cut enough light for suitably long exposures.

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    Senior Member Anson's Avatar
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    Default Re: CPL for ND purposes?

    Quote Originally Posted by vee5 View Post
    Good qn :-) I'm wondering the same thing too. I believe B+W is indeed better, but how much better? Would it be noticable to a noob like me? :P But having said tat I rather buy a good one now.. than having to 'upgrade' later.
    OT abit... I wonder did anyone do a comparison on the different CPL...How is the expensive CPL different from the budget?

  11. #11
    Senior Member zac08's Avatar
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    Default Re: CPL for ND purposes?

    Quote Originally Posted by Anson View Post
    OT abit... I wonder did anyone do a comparison on the different CPL...How is the expensive CPL different from the budget?
    From what I've heard, it's the colour cast difference. The better ones should not cause any colour cast.

    As for ND purposes...

    I have tried using 2 polariser filters to achieve such an effect and it does work.

    Use 1 C-PL and 1 linear polariser filters together and rotate the top piece at different angles, you will then see different amount of light cut off... it can almost cut off all the light...

    The experiment was done at home in front of a computer terminal, so I can't really be sure of how much light it can cut off totally... use at your own caution and after experimenting...
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    Default Re: CPL for ND purposes?

    Quote Originally Posted by zac08 View Post
    From what I've heard, it's the colour cast difference. The better ones should not cause any colour cast.

    As for ND purposes...

    I have tried using 2 polariser filters to achieve such an effect and it does work.

    Use 1 C-PL and 1 linear polariser filters together and rotate the top piece at different angles, you will then see different amount of light cut off... it can almost cut off all the light...

    The experiment was done at home in front of a computer terminal, so I can't really be sure of how much light it can cut off totally... use at your own caution and after experimenting...
    I read about the combined use of linear and circular polarizer to act as ND filter. There's a guy from Nikonians.org, noticed under certain (and rare) situation, the combined filters produced a bright, corner-to-corner "X" mark on the picture
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    Senior Member zac08's Avatar
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    Default Re: CPL for ND purposes?

    Quote Originally Posted by Randius View Post
    I read about the combined use of linear and circular polarizer to act as ND filter. There's a guy from Nikonians.org, noticed under certain (and rare) situation, the combined filters produced a bright, corner-to-corner "X" mark on the picture
    Have not tried that often enough to notice that.

    But thanks, will note of that if I do try this experiment again in future.
    Michael Lim
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  14. #14

    Default Re: CPL for ND purposes?

    Tks guys for all ur tips.

    I have a very stupid question. I saw someone demonstrate to me before, that he can totally cut off the light from a computer screen with a linear polariser.

    I just bought a B+W circular polarizer, expecting it to do the same thing with my computer screen. However, it has no effect at all as far as i can tell with my naked eyes. Is it supposed to be that way?

    If I can't see any effect with my naked eyes, how will I be able to adjust to the level of polarizing I desire? Hmm...

  15. #15

    Default Re: CPL for ND purposes?

    Pardon me for answering my own stupid question :P

    Apparently it only cuts off all light from a flat screen LCD monitor, not the old CRT monitors. Can anyone provide more insights?

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    Moderator Octarine's Avatar
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    Default Re: CPL for ND purposes?

    Quote Originally Posted by vee5 View Post
    Pardon me for answering my own stupid question :P

    Apparently it only cuts off all light from a flat screen LCD monitor, not the old CRT monitors. Can anyone provide more insights?
    You have achieved part one: try and see what happens. Good start. Now the conclusion: if a CPL is able to cut off the light emitted by an LCD then the LCD emits
    a) unpolarized light like any other lamp
    b) light of a certain polarization plane.
    More to read: http://www.great-landscape-photograp...ng-filter.html and http://en.wikipedia.org/wiki/LCD
    Last edited by Octarine; 14th January 2009 at 02:47 PM.

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    Moderator catchlights's Avatar
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    Default Re: CPL for ND purposes?

    Quote Originally Posted by vee5 View Post
    Tks guys for all ur tips.

    I have a very stupid question. I saw someone demonstrate to me before, that he can totally cut off the light from a computer screen with a linear polariser.

    I just bought a B+W circular polarizer, expecting it to do the same thing with my computer screen. However, it has no effect at all as far as i can tell with my naked eyes. Is it supposed to be that way?

    If I can't see any effect with my naked eyes, how will I be able to adjust to the level of polarizing I desire? Hmm...
    very simple, when you use the CPL filter for shooting, just rotate the ring...

    now you see it....., now you don't.......
    now you see it....., now you don't.......
    now you see it....., now you don't.......
    now you see it....., now you don't.......
    now you see it....., now you don't.......

    of course, if you want to have a nice blue sky, you need to have blue sky to begin with, and the sun lights suppose to be perpendicular to lens axis.

    and also, CPL filter not able to remove reflection from metallic surface..
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    Senior Member giantcanopy's Avatar
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    Default Re: CPL for ND purposes?

    Quote Originally Posted by Randius View Post
    I read about the combined use of linear and circular polarizer to act as ND filter. There's a guy from Nikonians.org, noticed under certain (and rare) situation, the combined filters produced a bright, corner-to-corner "X" mark on the picture
    The Vari-ND was thought to work on this concept. Now u need a reasonably good but big diameter circular polariser and a good quality linear polariser to DIY

    Quote Originally Posted by vee5 View Post
    Pardon me for answering my own stupid question :P

    Apparently it only cuts off all light from a flat screen LCD monitor, not the old CRT monitors. Can anyone provide more insights?
    Light from LCD is polarised but not light from CRT monitors. You can turn the filter in such a way where u totally cut off the light from the LCD monitor, In the case of a CRT u probably can dim it by only allowing the polarised plane of light across the filter while blocking others.

    As for linear and circular polarisers they are supposed to be almost equivalent although some will argue that IQ is theoretically better since there is an additional quarter wave plate in the circular polariser. But the idea is the circular polariser gives you reliable through-the-lens metering and autofocusing.

    Ryan

  19. #19

    Default Re: CPL for ND purposes?

    Tks Ryan and guys, I see light now lol. Looking fwd to play with my new toy.

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