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04-16-2012, 07:02 AM   #1
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CP filter question

Not sure this belongs here but can't figure where else to put it so here goes. (Monitor can move it if needed) Anyway, I've owned several CP filters thru the years and they all had index marks on them, so when using them I just matched up the marks. I recently purchased a thin profile CP for my UWA lenses that has no index marks on it. My question is this: How do I know when optimum polarization has occured? What I have been doing is turning the filter ring while looking thru the viewfinder until I get the least amount of light entering the camera (in Av mode I watch the shutter speed, in Tv mode I watch the aperture) there is generally one stop difference between the most and least amount of light reaching the camera's meter so when I get to that spot I continue to turn 1/2 way into the darkest portion of the range. However this is cumbersome in the extreme, and I'm hoping there is a better way of determining maximum polarization.

NaCl(always looking for the 'simple and dirty' tricks)H2O

04-16-2012, 07:34 AM - 1 Like   #2
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Not sure if it is the best way but I have always just looked through the view finder and turned until I got the effect I wanted, which is not always maximum polarization. Never thought to use the index marks to be honest.
04-16-2012, 08:51 AM   #3
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I have 4 CPL filters and none have index marks - that would be nice.
04-16-2012, 10:00 AM   #4
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With a couple of my CPLs, there's a white dot on the outer ring but no marks on the inner ring, so the white dot is amusing. Other CPLs have no index marks at all. To judge polarization, I half-hold the shutter button and watch exposure data change in the VF. Lowest shutter speed or widest aperture or highest ISO = maximum polarization.

04-16-2012, 11:53 AM   #5
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RioRico that's what I'm doing with the low profile one I have now. But it's a pita. I'll try jatrax's method. It seems a lot easier than holding the shutter button half way with one hand, turning the filter ring with the other and trying to keep the camera steady and pointed exactly to the same spot. I know it can be done, I do it, but it's still a pita.

NaCl(as I get older I get lazier...and grumpy too!)H2O
04-16-2012, 12:17 PM   #6
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QuoteOriginally posted by NaClH2O Quote
RioRico that's what I'm doing with the low profile one I have now. But it's a pita. I'll try jatrax's method. It seems a lot easier than holding the shutter button half way with one hand, turning the filter ring with the other and trying to keep the camera steady and pointed exactly to the same spot. I know it can be done, I do it, but it's still a pita.
Oh, I don't recalibrate for every shot! I usually find the max-polarization position and leave it there. Exceptions:

1) I most commonly use CPLs on very fast non-A-type lenses like the Vivitar-Kiron 24/2 (with iris blades stuck wide open) or my K50/1.2. I'll in sunshine with with CPL on, adjusted so my K20D's shutter stays below the flashing 1/4000 second warning. If I go into lesser light I either switch to minimum polarization or just remove the CPL.

2) With a CPL on slower lenses, I only adjust polarization to accommodate the shutter.
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