Hi Lex,
At Tuesday, August 08, 2000 1:50, Lex Jenkins <lexjenkins@xxxxxxxxxxx>
spoke about *Re: [OM] Polarizers and ND filters...* saying
> Tom, I don't know how many different ways to restate this to get the point
> across:
>
> Polarizers do not reduce *all* reflections. Where there is no glare *within
> the effective range* of a polarizer, the polarizer has *no* effect on a
> photograph other than to serve as a neutral density filter. In such cases
> there is *no* effect on the metering of a scene.
True. But not all glare comes from glass or sky.
>
> That is not to say that a polarizer will not improve the color saturation of
> objects in a scene which do reflect glare that is within the effective range
> of a polarizer. But it doesn't necessarily follow that this will have any
> effect on metering of the scene. To put it simply, it depends.
Usually the glare is only a minor part of the picture, so eliminating
or enhancing it will cause very little change in the metering. But
this is not always the case. For example, eliminating a sun
reflection may change the measured light by a stop or more.
The metering thru the polariser will be more accurate than an hand-
held meter reading without a polariser in the same orientation.
>
> The simplest example that can be replicated at home is to use a painting
> beind glass and a typical television with a curved screen. While facing the
> painting head-on the polarizer will have zero effect on any visible
> reflections from room lighting, etc. However, *some* reflections visible
> from the TV screen can be reduced regardless of where we stand in the room -
> but it is not possible to reduce *all* reflections from a curved (or any
> complex) surface with a single polarizer on the camera.
Agreed. Light is more polarised by
>
> You and I aren't disagreeing, but we do seem to be stuck in a rut of
> nitpicking. I'm out of nits on my end, tho'.
Polarization definition/explanation:
http://projects.ghostwheel.com/dictionary/Polarization
What I'm suggesting is that polarising filters are useful in far more
situations than just when you have glass or blue sky:
1. They can increase - or decrease - the colour saturation in many
situations, depending on the orientation of the filter. Polarised
reflections can be diffuse light from rough surfaces, e.g. leaves,
flowers, rather than the image you might get from a smooth surface.
2. They are an opportunity for changing the rendition of a scene that
is only available when you take the picture, since the film doesn't
record polarisation. This is unlike colour filters whose effects can
be (mostly) replicated when making a print or copy slide.
3. By increasing or decreasing glare, they give the photographer a
way of changing the scene and emphasizing or deemphasizing different
sources of polarised light, e.g. rainbows.
4. The most accurate metering is thru the filter.
5. You may not like the effect. For example, the tempered glass of
car windows polarises light in a checkerboard pattern which you
probably don't want.
In other words, try it for yourself. It's another tool with wider
uses than just situations with sky or glass.
Tom
------------
Tom Trottier <TomATrottier@xxxxxxxx> ICQ: 57647974
Abacurial Information Technology Consulting
400 Slater St. Suite 415, Ottawa ON Canada K1R 7S7
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