On 2/25/2015 9:39 PM, tOM Trottier wrote:
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.
Yes, and that is no longer necessary with digital processing, for many types of filters. I say those are not necessary
in order to get the same effect, not that the effect is desirable or not.
Polarizers filter out light polarizations.
Yes, and that can't be duplicated in post. Which is why it's on my list.
Infrared filters only let through infrared light.
Ah, forgot about those. I've never liked IR photos, so it's not on my radar. Still, it fits my "I can't see the point of
using" criterion :-)
UV filters only let in UV light.
That's a possible usage, but one which will be regularly misunderstood. In common usage, a UV filter diminishes UV. I
say diminish because the common ones filter out little.
Close-up filters change the focal length of the lens.
That's just a common misnomer. All other filters are flat glass. The 'filters' to which you refer are more properly
close up lenses, 'cause, well, 'cause that's what they are, lenses, not filters. They refract light, not change spectral
composition, polarization, etc.
Coloured filters reduce differentially which wavelengths pass through.
For B+W film, coloured filters affect the tones caused by different colours
Both of these are the same thing, stated in two ways, and much more easily and
controllably applied in post.
and can control coloured flare better.
Wow, that's obscure. Have you ever actually done that?
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.
That's what AG is arguing. How many people can say they successfully do that? It implies a great deal of knowledge about
both the light being captured and the characteristics of the sensor system.
I just don't think it's needed with contemporary sensor systems and much
simpler technique
It can also reduce flare.
That I'm not understanding. If I use a colored filter to reduce flare that's of a single color, that ONLY works if that
color isn't part of the rest of the image. The vast majority of flare I deal with is fairly broad spectrum, overlapping
with most of the rest of the subject content.
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.....
Well, I've said it before, and here I go again. All lovely theory/ideas, but is anyone using them other than in very
specialized studio work?
Over and over, I bracket exposures, thinking I will need them for combining for greater DR. Over and over again, I find
that the one that just comes up to the top of the histogram (what that means depends on the specific sensor system) is
sufficient by itself for a natural looking depiction of the subject without clipped highlights or lost shadows.
What I do works, and works very well, for my work. What you suggest would mean hardly ever taking pictures - for me.
It's endless experimenting with tests, then remembering the settings and filters for different subjects.
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.
Oh come now. The mixed colors may be manipulated just as easily by changing the mix of primaries. The Hue/Saturation
tool in PS, as an example, offers exquisitely detailed control of any/all colors.
If you want to filter in or out more particular wavelengths than those broad
ones, you need glass filters.
My comment was limited to commonly used photo filters. Look at some transmission curves of even the finest ones. They
are quite broad band, with very long shoulders, not sharp cutoffs.
Astronomers use filters extensively since particular wavelengths correspond to
different elements (maybe
compounds?) which generate or filter out particular wavelengths.
Again, I'm talking terrestrial photography. Are you using the expensive, specialized astro filters for your non-astro
photos?
It appears you've dropped into a long, off and on discussion, without knowing what has come before. My comment to which
you respond is a much shortened version of what I've posted in greater detail before, both in the last day or so and
earlier. Just a reminder of a previously stated position.
You have, BTW, left out one quite important use. At higher elevations, there is proportionately more UV. Because most
color film and esp. most digital sensors, can't differentiate between visible blue and UV (those pesky broad spectrum
filters again, over sensel/pixels), it is impossible later to remove the UV created blue from other blues. The only
solution is a much more powerful filter than the usual UV filters useful mostly for lens protection. An 81A or 81C
filter is the solution, along with occasional shots of neutral targets.
With reference targets, or even just some known white things in subjects, it is easy to recover from any over filtering,
while under filtering is not fully recoverable.
Eyes Wide Open Moose
--
What if the Hokey Pokey *IS* what it's all about?
--
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