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Forum: Pentax DSLR Discussion
02-28-2013, 07:54 AM
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Yup. I want tethering too. Couldn't believe they took it away.
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Forum: Pentax K-5 & K-5 II
09-17-2011, 06:30 AM
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Originally posted by wizofoz
Wizofoz and eddie1960, There should be an exposure difference in this scene caused by rotating the linear polarizing filter. Direct sunlight is essentially unpolarized, however sunlight reflecting off a pool surface (water) will be polarized to a degree (depending on angle of reflection - maximum occurs at Brewsters angle, for water, n=1.33 => Angle_Brewster~=53degrees ). Therefore Wizofoz's observation of exposure differences with different linear polarization filter orientations of this scene with sunlight reflected off pool water is consistent (but does not definitively show error).
At the "perfect" angle of reflection the sunlight reflecting off the pool's surface will have maximum polarization, and when observed through a linear polarizing filter rotated through 90 degrees will show maximum variation of the reflected light intensity. When the filter is oriented to admit vertically polarized light, the sun's reflection off the water will be filtered out and disappear to the eye and to the camera looking through that filter. Less light coming into the lens, greater exposure needed. To complicate maters more, skylight (sunlight scattered off air) is also partially polarized (maximum at 90 degrees from the sun) and if that light was also in the scene, the polarizing filter's orientation could influence its intensity as well.
From Wizofoz's comments it does not appear that there is any significant exposure error introduced by the linear polarizer.
To most sensitively test the effects of a linear polarizing filter's orientation on exposure error, shoot a scene of direct sunlight reflecting off a sanded (rough) un-coated metal surface. This light will remain unpolarized and any orientation of the linear polarizer should not affect the exposure. If it does - then the exposure metering system is sensitive to the polarization of the incoming light and it will introduce errors.
Ditto for a test of the AF system and the effects of a linear polarizer, but this might be more complicated because the K5 seems to use different focus methods in different situations.
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