polarizer or neutral

I just bought a Kenko PL 55mm polarizer but seems to be a neutral
filter instead. When I turn the ring I see no difference in light. Does
anyone know if that could be a neutral filter o it's just I don't know
how to turn the ring. I really cannot see a slight difference in light
through it when turning the ring.

Thanks for the responses.

Dooban wrote:
I just bought a Kenko PL 55mm polarizer but seems to be a neutral
filter instead. When I turn the ring I see no difference in light. Does
anyone know if that could be a neutral filter o it's just I don't know
how to turn the ring. I really cannot see a slight difference in light
through it when turning the ring.

Thanks for the responses.

Try pointing the camera up at a blue sky or point at an angle through a
window and try.

Scott

A google search shows the PL as a polarizing filter, but it's an easy
check to see if it is.

Get another polarizing filter if you have one or a pair of polarized
sun glasses and stack them. Then rotate them against themselves. If
it is polarized, you can tell. Where the polarizing crosses, it will
be very dark.

If there is no change when you rotate it, it is likely circular
polarization, which is what you generally want on an autofocus lens.

The other way to test it is to find some glare, preferably outside, and
look through the lens at it. Inside and other places without much
glare, a polarizing filter will have little effect.

Like they said, a polariser *is* an ND filter if there is no polarised
light coming through it...

Try it on a blue sky near midday. When pointed directly towards or
away from the sun you will see little or no effect, but when pointed at
90 degrees to it (eg, skies near the horizon at midday) the effect will
be dramatic. Try it over river- and ocean- views where there is a lot
of reflection off the water. Lastly, try it looking at glass windows
with lots of reflections, but at about 45 degrees, *not* straight on..

If, after all that, you *still* can't see the difference as you turn
it, it *is* just an ND filter, or your eyesight is severely challenged!

Pat wrote:
A google search shows the PL as a polarizing filter, but it's an easy
check to see if it is.

Get another polarizing filter if you have one or a pair of polarized
sun glasses and stack them. Then rotate them against themselves. If
it is polarized, you can tell. Where the polarizing crosses, it will
be very dark.

If there is no change when you rotate it, it is likely circular
polarization, which is what you generally want on an autofocus lens.


This depends on both which way you have the filter pointed. If you
have the front of the filter towards the polarizing sunglasses then you
see a variation in the transmission as you rotate the filter.

Scott

wrote:

: Unless you mean the rotating part of the filter is separate from the
: threaded part, which is sorta self-evident.. I think the OP is
: suggesting that it could be an ND filter accidentally loaded into a
: polariser assembly.

That was the way I read it. If the OP is trying to tell the if this
properly manufactured filter is a ND filter or a Pola. In this case the
visual inspection showing that the filter has the ability to turn the
filter media seperate from the filter threads would identify a Pola. But
if the incorrect filter media is installed in a filter mount (very
unlikely but possible) then these tests that use two pola filters,
counter-rotated against eachother would definatively show that the filter
media in question is or is not a Pola.

But as has been pointed out the OP seemed to indicate in the original
posting that they were unsure if this "Pola" is really a Pola due to not
seeing powerful changes as the filter is being rotated. And as has been
pointed out such a drastic optical change may not be evident in all
situations. And thus it may be simply a case of mistaken expectations on
the part of the OP. In which case some of the earlier replys probably took
care of helping the OP and some of the followup "tests" may be able to
help the OP test the filter in question to ease their own mind.

IMHO I would suspect that most well known filter manufacturers perform
some form of quality control and thus the likelyhood of an incorrect
filter media installed in a Pola filter mount getting out into the public
is vastly unlikley (not totally impossible but very unlikely).

Randy

==========
Randy Berbaum
Champaign, IL

Thank you all for the responses. It's incredible the amount of
knowledge and solidarity one finds in usenet. Finally I am going to
take a look to my physics 101 book because it seemed I didn't get the
theory very well. As some of you have pointed out I wasn't looking at
proper light sources nor accurate angles so I could not see any
difference when turning the ring. When doing so I realized I have a
goog PL filter (linear). Thanks (blush)

Thank you all for the responses.

And thank you, Dooban, for returning to the thread and acknowledging
the replies! I trust you are aware that a linear polariser may cause
problems in cameras that use 'beam-splitters' and/or folded light
paths? In essence that means you need to be careful if using the
filter on most SLRs, or any other camera with that type of system.
Linears *can* cause problems with both the focus and exposure, but it
is still possible to use them successfully.

Thanks Mark for your interest. Yes I am aware of linear polarizers
problems with SLRs. Mine is a Lumix FZ30 and still don't know if the
linear would cause any problem, I guess I'll have to check and see, but
at the moment it woks perfectly well.

THomas, the main problem I had was not using the correct angle against
the Sun when focusing to a reflection. When at 45º the filter works as
it should. Thanks anyway.