In article , Dan Lau <dlau@xxxxxxxxxxxxxxxx> writes
>
>Thanks to everyone who answered my questions. But since Polarizer
>filters are new to me, Jim has raised another issue that I want
>to learn. My understanding of a circular polarizer is that there
>is no "direction" to it, unlike the linear polarizer; so why would
>a circular polarizer need a "V" marker? And why does a circular
>polarizer need to be freely rotatable on the lens?
>
>Since now I have the filter, I'd like to learn as much about using
>it as I can. And again, I appreciate all the posts on this
>subject. Thanks again.
> -Dan
>
Hi Dan,
your impression of the circular polariser is almost correct.
There is no asymmetry of the output - the light passed by the polariser
behaves ALMOST as if it is unpolarised. However the filter still
polarises light by only letting one orientation pass through.
The circular polariser is really two specialist filters sandwiched into
one. The first part is a normal linear polariser, and this works as you
expect on the light that passes through it. The V on the filter shows
the orientation of the polarisation. The second part of the sandwich is
a special filter called a quarter wave plate. This splits the polarised
light from the first part into two parts and rotates one of them by
90deg, like an X. That is why the output of the circular polariser
APPEARS to have no asymmetry - because as one of these polarisations
reduce in intensity the other one increases to compensate for it
perfectly.
So as far as the scene you are photographing is concerned, the circular
polariser behaves just like a linear one, but to your camera it appears
as if it is not polarised at all.
--
Kennedy
Yes, Socrates himself is particularly missed;
A lovely little thinker, but a bugger when he's pissed.
Python Philosophers (replace 'nospam' with 'kennedym' when replying)
< This message was delivered via the Olympus Mailing List >
< For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
< Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >
|