> I took an additional photo of the tree with a #25 red filter attached.
> When viewing it in Olympus Viewer (OV) I noticed that the histogram was
> largely off-scale at the top. This may be why I get the blanket grey when
> converting to JPEG B&W. But that does not explain the ongoing problem with
> the emulated red filter.
Hmm. Sounds like you pushed the exposure up to compensate for the red
filter. Shoot it again with the same exposure as with no filter.
Here's why this works this way:
There are 3 (or four) different color sensels. One is sensitive to the
red spectrum, one is sensitive to the blue spectrum and one (or two)
is sensitive to the green spectrum. (Very important to recognize that
the mix of green to the others is not 2G:1B:1R, but usually 1G:1B:1R).
Let's assume a sunny-sixteen scene:
An unfiltered ISO 100 exposure would be F16 at 1/100 or equivalent.
With digital this properly exposes all three sets of color sensels.
If you place a red filter on the lens, it blocks the light going to
the green and blue sensels, but the red sensels are unaffected.
Therefore, what happens is that the red sensels with a red filter are
still exposed at sunny sixteen exposure regardless of what the meter
says. You have a monochrome sensor at this point and the filter isn't
altering the exposure value at all.
So, I'm assuming, from your statement, that you ended up over-exposing
the sensor by letting the meter get fooled by the filter or by all the
years of history in applying a filter factor to the exposure.
--
Ken Norton
ken@xxxxxxxxxxx
http://www.zone-10.com
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