Exposure with a CPL Filter


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Aug 25, 2007
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#1
When you are using a circular polarizer, does the camera compensate the exposure automatically? Of course, this is under the assumption that you are using Av or Tv. Or do you have to adjust your exposure yourself even when using Av or Tv?

I am asking because i have noticed that in my shots whenever the filter is on, it is not only the sky that goes dark, but also the other elements in my picture.

I am using a Hoya CPL by the way.

Thanks in advance!
 

dzignous

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Aug 10, 2006
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#4
Yes, CPL will normally drop exposure by around two stops. E.g if you are using Av, your shutter speed will be slower by two stops and vice versa.;)
 

roygoh

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#5
See for yourself. Fix the camera on a tripod, set to Av or Tv, and check the shutter or aperture settings the camera picks on the same scene with and without the CPL mounted.

The exposure should be higher when teh CPL is mounted, i.e., longer shutter time or larger aperture, if the scene and lighting condition remain unchanged.
 

#7
As everyone has pointed out, you exposure will drop by about 1.5~2 stops when using a CPL. This effect, in terms of brightness of the image, may be exacerbated depending of what you are photographing and how you apply the filter. The camera may meter your settings as being correct and yet the image is much darker than you anticipated. I tend to use bracketing a lot more when I'm using a CPL filter since the results can ocasionally surprise you. :)
 

mrchua

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#8
See for yourself. Fix the camera on a tripod, set to Av or Tv, and check the shutter or aperture settings the camera picks on the same scene with and without the CPL mounted.

The exposure should be higher when teh CPL is mounted, i.e., longer shutter time or larger aperture, if the scene and lighting condition remain unchanged.
i thought the exposure would drop with a polarizer, causing underexposure.?
 

roygoh

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#9
i thought the exposure would drop with a polarizer, causing underexposure.?

The polarizer will decrease the light throughput, but the camera metering will compensate for that by increaing the exposure.

If the camera setting is fixed to give a correct exposure without the CPL, then yes, adding the CPL will cause the picture to be underexposed.
 

Aug 25, 2007
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#10
Thanks for all the replies. I guess it's better to bracket your shots then
 

attap seed

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#11
Thanks for all the replies. I guess it's better to bracket your shots then
if u bracket w a CPL, then i tink u better bracket ALL your shots. cus u must know wat u wan. if u dunno, anything (or nothing) is going to do.
 

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