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Old Feb 2, 2005, 7:01 AM   #1
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I guess this is the place for my question, it affects lenses after-all.......

I recently got a new lens and a circularpolarising filter to go with it. As soon as I took out the polarising filter it was immediately apparent that the filter was dark; very, very dark. First thing I did was to attach the lens to my camera (minus polariser) and take a meter reading with the lens fixed wide-open under aperture priority. Then I attached the filter and took another reading with the camera focusing on the exact same spot as before.

Near as I can figure it the polarising filter is costing me between 2.5-3 stops of light. One of the reasons I chose the new lens I had gotten was because of it's f2.8 aperture wide open. Does this lens, with the polariser attached,now have the light-gathering ability of an f5.6 - 6.7 lens?

The polariser is a Hoya standard circular polariser with a 77mm diameter.Even then itdidn't come cheap. Is what I am seeing, 2-3 stops of light lost,normal for a polarizing filter of this size and make? I have used a cheapie 52mm polariser filter before on a different camera and it caused little if any measureable light drop-off. Is it simply because the Hoya is so large that it drops so much light?

I was using the camera today in relatively bright conditions so the polariser caused me no problems with slow shutter speeds, in fact I was quite impressed with the deep blue coloursit was capable of producing in the sky.
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Old Feb 2, 2005, 11:05 AM   #2
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It's normal!

How much light loss depends on the rotation (ie the angle) of the polarizer to the sun (ie the effect is variable), but you definetely lose some stops
http://www.schneideroptics.com/filte...hy/polarizers/


BTW there's less light; however the f/number hasn't changed - It's like the sun has lost intensity, but the DOF stays constant!
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Old Feb 2, 2005, 1:17 PM   #3
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On that site,when he says filter factor is 2.3 - 2.8 is he saying that the filter is causing a loss of 2.3 to 2.8 stops?

I knew the polariser would cause some measure of light loss it just took me by surprise how much light it blocked. Honestly, the filter glass looks like it could have come from a pair of sunglasses it's so dark!

I am happy with both the lens and the filter though, the blue sky came out brilliantly using the polariser. Far, far better then the cheapie 52mm filter I had on the other camera was capable of producing.

When I get time i'll post some ofthe pics I took today.
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Old Feb 2, 2005, 2:22 PM   #4
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redundo wrote:
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On that site, when he says filter factor is 2.3 - 2.8 is he saying that the filter is causing a loss of 2.3 to 2.8 stops?
Yeap - Except may be for the UV, most will will have some loss associated (ie filter factor), albeit small: http://www.schneideroptics.com/filte.../uv_&_warming/


PS look through the lenses with a white paper behind them... some has pinkish tint in them already so no need for 'warming' filters here (and save yourself a few decimals) :-) :lol: :G
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