Hi Chip,
At 2000 May 28 - Sunday 8:46, Chip Stratton <olympus@xxxxxxxxxxxxxxx>
spoke about *RE: [OM] photographing polished met...* saying
>
> > Wayne wrote, of cross-polarisers and flash:
> > > More bad news: Reflections from an electrically conductive
> > > surface are not polarised, so using the polarisers doesn't help.
> >
> > I think I disagree. Surely the thing about metallic surfaces is that
> > they have no polarising effect, so if the light is polarised in a
> > particular plane when it hits the surface, it stays polarised
> > afterwards.
> >
> > The converse is if you have something like water, which does
> > polarise. You only need one polarising filter to stop reflections
> > from water (if you're at the right angle) because the polarising
> > effect of the water itself is doing the same job as the part of the
> > cross-polariser on the flash.
> >
> > Does that make sense?
>
> Here is the problem I as I see it. Since metal does not change light
> polarization, ANY light hitting it from the flash comes back without
> polarization change. If the flash cross polarizer is used, all light
> coming from the flash and reflected back from the metal surface is of
> one polarization, and should be 'blocked' by the lens polarizer.
> Now polarizers work imperfectly, and the cross polarized light that
> does make it past the second polarizer usually has a strong color
> cast. When I used the T10 and cross polarizer to photograph a natural
> gold nugget, the gold became very red.
>
> My guess is that non-metallic surfaces work with flash cross
> polarization because some of the light reflected back DOES undergo a
> polarization change induced by the subject, and makes it past the
> second polarizer. 'Hot spot' reflections on such a subject presumably
> don't undergo polarization change on reflection, and should be
> largely blocked by the second polarizer.
>
> Therefore, I don't expect good results when using the cross
> polarized flash technique when the subject is a metallic object.
>
> Is this perfectly muddy?
Sounds clear to me, but hey, lets not polarise on the topic...
Use one polariser, either on lens or on light for metals.
On light is better for image quality.
Tom
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