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Re: [OM] Mirrorless polarizers

Subject: Re: [OM] Mirrorless polarizers
From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxxxxxxx>
Date: Thu, 20 Mar 2014 21:06:39 -0400
I recommended that Don post his test results since, after examining them 
myself side-by-side I couldn't see any difference at all in the focus of 
the three images.  All 3 are tack sharp despite the fact that the lens 
being used is a 4/3 rather than M.4/3 lens on an E-M1. For 4/3 lenses 
the E-M1 incorporates phase detect focusing elements in the sensor which 
are (by conventional wisdom) befuddled by linear polarizers.  That is 
clearly not the case with the E-M1.  On that camera, linear polarizers 
clearly work as well as circular polarizers.

I was initially concerned that maybe the test wasn't really valid. 
Maybe Don had set up the focus with no polarizer first and then left it 
that way as he changed filters.  But that's definitely not true.  In 
fact the camera was powered down between filter changes and then 
refocused with the filter in place.  All 3 images are tack sharp.

All that said there is a slight difference in exposure between the 
images.  I don't know why that is true but don't believe it has anything 
to do with filters on an E-M1.  There are no beam splitters in the 
E-M1's exposure readings taken directly from the sensor.  Whatever cause 
the slight exposure change was not something being tested.

Chuck Norcutt

On 3/20/2014 3:02 PM, Don Holbrook wrote:
> http://zone-10.com/tope2/main.php?g2_itemId=11917
> Sometime back Chuck Norcutt, and perhaps others, brought up questions about 
> polarizers on mirrorless cameras.  I offered to take some shots and send to 
> Chuck.  He suggested I put them on the web site.  so here they are (this one 
> and the next two.....no polarizer, linear, and circular).  Tripod, remote 
> release, sun on left, center spot autofocus.  No scientific claims.
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