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Polarizer(s) questions

 
 
Eric Miller
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      08-04-2011
Is it necessary to use a circular polarizer with contrast detect auto-focus?

If so, would two circular polarizers work for a variable ND filter on
such a camera? (Just for indoor portraits, web resolution)

Eric Miller
www.dyesscreek.com
 
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nospam
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      08-04-2011
In article <j1cta0$5al$(E-Mail Removed)>, Eric Miller
<(E-Mail Removed)> wrote:

> Is it necessary to use a circular polarizer with contrast detect auto-focus?


circular polarizers are only required if there's a beam splitter in the
optical path.

> If so, would two circular polarizers work for a variable ND filter on
> such a camera? (Just for indoor portraits, web resolution)


use one circular and one normal, with the circular polarizer closest to
the camera.
 
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PeterN
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      08-04-2011
On 8/3/2011 9:39 PM, Eric Miller wrote:
> Is it necessary to use a circular polarizer with contrast detect
> auto-focus?


Generally yes. While some autofocus systems will work with a linear
polarize, you should test your system.

>
> If so, would two circular polarizers work for a variable ND filter on
> such a camera? (Just for indoor portraits, web resolution)


I use a circular + a linear with the circular closest to the lens. the
disadvantage is that you don't get true neutral density, you will lose
some specular highlights that you want in your image. But the cost is
substantially less than a variable ND filter.

--
Peter
 
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