2015 Feb 25 - Wed at 16:30 re:Re: [OM] Spotmeters …
Moose <olympus@xxxxxxxxxxxxxxxxx>wrote
…
>All that said, I can't see the point of using glass filters other than
>polarizer, ND and 81A or C for high altitude.
>
>Color Me Puzzled Moose
…
The reasons for glass (or gelatin) [ie, exposure-time] filters are to restrict
or shape the light in
some way. Polarizers filter out light polarizations. Infrared filters only let
through infrared light.
UV filters only let in UV light. Close-up filters change the focal length of
the lens. Coloured
filters reduce differentially which wavelengths pass through.
For B+W film, coloured filters affect the tones caused by different colours and
can control
coloured flare better.
For colour film or digital colour cameras, a coloured filters can match the
range of the
incoming light to the colour sensitivities of the sensor or emulsion layer so
that the high and
low ends of each colour histogram fit in each colour sensor's or layer's
acceptable range ,
capturing more detail in highlights and less noise in shadows. It can also
reduce flare.
Then you can reverse the colouring digitally and end up with more detail or
less noise with a
brightness range larger than what your camera is capable of in an unfiltered
exposure. That is
what HDR can do too, with a static subject and camera and no colour
pre-measurements.
(Colour spaces like ProPhoto and AdobeRGB and sRGB are also brightness spaces.
They
constrain which brightness values/range can be coded.)
So coloured glass filters can improve single exposures by reducing noise and
capturing more
detail. They are "Dolby noise-reduction" for light... though they do not
compress, like Dolby
does, rather they can match the incoming light range to what the sensor/layer
can record.
(showing my age...). More like Dolby HX.....
In addition, post-facto filtering just means changing the R, G, or B (& Cyan
for some Fuji
cameras) values, stretching,compressing., reducing, or increasing them. If you
want to filter in
or out more particular wavelengths than those broad ones, you need glass
filters. Astronomers
use filters extensively since particular wavelengths correspond to different
elements (maybe
compounds?) which generate or filter out particular wavelengths.
tOM
-- Absum! -- Quidquid latine dictum sit altum viditur.
tOM Trottier +1 613 860-6633
tOM@xxxxxxxxxxxxx Skype:Abacurial
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