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,
--
_________________________________________________________________
Options: http://lists.thomasclausen.net/mailman/listinfo/olympus
Archives: http://lists.thomasclausen.net/mailman/private/olympus/
Themed Olympus Photo Exhibition: http://www.tope.nl/
|