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Re: [OM] Which Grad ND system if any do you like?

Subject: Re: [OM] Which Grad ND system if any do you like?
From: Ken Norton <ken@xxxxxxxxxxx>
Date: Wed, 2 Jun 2010 18:06:36 -0500
> Same thing with white balance, if you let the camera do it (e.g. for tungsten 
> lighting) the blue channel gets approximately 2 stops less light than the 
> red, then when you boost the blue in raw conversion you pull in extra noise 
> and also reduce your effective dynamic range by 2 stops.  Better to use an 
> 80A filter to get the WB at least close then just make small adjustments in 
> post processing.


Yes, but the hazard there is that with the 80A filter you are lowering
the effective sensitivity of the green and red channels to match the
blue channel. If you compensate by raising ISO then you end up
increasing the noise and decreasing the dynamic range of the other
channels to align themselves with the blue channel.

The question then becomes which is worse?  Increasing noise in the
green and red channels to match the noise of the blue channel? Or is
it possible to negate the effect of the blue-channel noise enough to
make it a non-issue?  If we are able to maintain a low ISO and
adequate shutter speed then using an 80A filter should be the
no-brainer, but using the filter may instantly compromise the rest of
the image-processing chain.

In my own experience, when adjusting white-balance in post for a
tungsten lit shot, I'm good to go UNLESS there is a need to pull up
the shadows. The lower ranks of the tonal range start to turn really
mushy and blotchy. Typically correcting for tungsten pretty much
boosts up the blue channel by around two stops. Anything from Zone IV
on up is perfectly fine, but below that point there is enough nasties
in there to make pulling the shadows up a disaster.  If, however, you
use the 80A to get in the neighborhood, the shadows should end up less
blotchy because the blue channel is "optimized" in-camera.

AG
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