I think Carlos' approach using an 80A filter has some vaidity.
The exposure is properly balanced over the RBG channels so less chance of
saturating the Red in giving adequate exposure to the Blue. This means that
each channel is operating in the same exposure region of it's "characteristic
curve" - compare this with film. The end result being that the noise should be
more equally distributed across RGB channels and I expect this has some benefit
in reducing noise reduction artifacts.
...Wayne
> -------Original Message-------
> From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxxxxxxx>
> To: Olympus Camera Discussion <olympus@xxxxxxxxxxxxxxxxx>
> Subject: Re: [OM] ETTR with the Sekonic L-508
> Sent: 13 Oct '11 03:00
>
> I think you're only considering the favorable half of the pie and
> ignoring the unfavorable half. It's an interesting concept that, by
> using a blue filter, you have avoided having to increase exposure on the
> blue channel in post processing. You think you have avoided noise in
> the process and so you have. However, the act of using the filter has
> also increased the total exposure time and has thus introduced
> additional noise across all channels. It's not clear to me that you
> have gained anything of significance.
>
> Chuck Norcutt
>
>
> On 10/12/2011 9:57 AM, Carlos J. Santisteban wrote:
> > Hi Chuck and all,
> >
> >
> > From: Chuck Norcutt<chucknorcutt@xxxxxxxxxxxxxxxx>
> >> Sorry, I didn't follow your logic about decreasing effective ISO. Can
> >> you first define "effective ISO"?
> >
> >
> > OK, I think I'm mixing two related, but not identical concepts here. By
> > 'effective ISO' I understand the achieved exposure value for a certain
> > lighting conditions. _Overexposing_ with the intent of recovering the
> proper
> > tonal scale in post (be it on digital or film) means going to exposure
> > values 'just right' for a lower ISO, thus _decreasing_ that 'effective
> ISO'.
> >
> > On the other hand, assuming that most sensors' native WB is close to
> > daylight (5500 K) the Tungsten setting is achieved by _cranking up_ the
> blue
> > channel gain, and possible decreasing the red gain... The blue channel with
> > its 'boosted ISO' is going to be the major contributor to noise in
> > Tungsten-WB shots -- it is in my current GF1 and was that way in the
> > EOS-300D.
> >
> > Using a 80A filter instead of the WB setting means getting the blue channel
> > back to a reasonable gain, increasing picture quality as per my experiment.
> > But the exposure correction for the filter factor (x4) implies exposure
> > settings of a _quarter_ of the set ISO (e.g. 200 instead of 800).
> >
> > It's likely that shooting at that reduced ISO without filter but on
> Tungsten
> > setting won't get the blue channel gain any higher than with the filter on
> > (and high ISO + daylight WB) but haven't actually tried.
> >
> > Cheers,
> --
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