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"Sports" Polarizer

 
 
Pat
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      07-12-2007
On Jul 12, 9:28 am, BaumBadier <(E-Mail Removed)> wrote:
> On Thu, 12 Jul 2007 13:19:57 +0100, Rob Morley <(E-Mail Removed)> wrote:
> >In article <(E-Mail Removed) .com>,
> >(E-Mail Removed) says...

>
> >> Austin, I think *you* need to read the op more carefully. It *isn't*
> >> a 'circular' polariser (as we know it), that Pat has described.

>
> >It seems to me that he /did/ describe a circular polariser, and then
> >added "It is NOT to be confused with the current circular
> >polarizer". So he's trying to find something that is functionally
> >identical to a circular polariser, yet is somehow different in a way
> >that he doesn't seem to be able to explain. Or am I missing something?

>
> I recall, way back when, that some special-effects polarizers were made by
> carefully cutting thin wedge shapes of the polarizing material and then
> reassembling them into other configurations to see what they would do.
> Eventually they became used as novelty weather-man's TV icons on their
> weather-map boards during B&W TV days. Where the weather-map was illuminated
> with a rotating polarized light and their sun and rain markers would "move" in
> bands of brightness as the rotating polarized light hit them. The sun icon
> slowly rotating in a star-burst pattern, or concentric waves from center to
> edge, or the rain icon would slowly move in a downward slant in bands of light
> and dark. Or the H and L pressure area markers would have all their little
> triangles or semi-circles have waves of light and dark pass through them in the
> direction that front was moving. (Or conversely a slowly rotating polarizer was
> in front of the TV camera's lens instead of a studio-light, I know not which,
> both would work, I only figured out how they were doing it at the time by
> observation.)
>
> If linear polarizing material was cut into narrow wedges with the plane of
> polarization either perpendicular to or in line with the length of the wedge,
> and then assembled of thin pie-slices so that (for all intents and purposes) the
> polarization was in a concentric orientation, or in a ray-burst configuration,
> then rotating that polarizer would not change its overall effect. If it was
> constructed to have the polarization planes in a concentric orientation then the
> part above the horizon would indeed darken the sky some. In total though, all
> light entering the lens would cancel out the polarizing effect for anything in
> the center. Because that light would pass through all parts of all the
> polarizing planes. Only things nearer the edges of the FOV would be affected.
>
> Perhaps this is how it was done and the type of device you are refering to? If
> it is not available you could obtain some sheet polarizing material
> (www.sciplus.comoffers some at times) and manufacture one for yourself using
> the above mentioned method. I'm not sure how good you could get with an x-acto
> blade and carefully mounting the thin wedges between glass so that it appeared
> nearly seamless, but if I was pressed to recreate that kind of thing I'd give it
> a good try.
>
> Do you recall at all if you could see some very fine lines radiating from the
> center of that polarizer? If so, that would reveal how this was done.


I don't remember if you could see the lines or not. I'm starting to
believe it was, as you said, some sort of novelty thing.

It did, however, act as you described. It darkened the sky away from
the center of the image. It never really cut much glare near the
center because you didn't have much glare there to start with. That
was usually the person you were photographing. I never used it on
NASCAR or something where the object itself would be glaring, so I
don't know what it would do.

I have no idea how they made/make polarizing material, so I can't help
you there but I don't remember any obvious lines on it.

Here's a though that I am just pulling out of the air. Look at a $20
bill and look at the micro printing. They can print really small when
they want to. Could it have been printed in a circular pattern or
spiral pattern?

Darn, I wish I still had it. It must be worth a fortune on eBay.

Believe it or not, it worked pretty good. It wasn't as good as a
"regular" polarizer, but you never had to adjust the orientation. In
fact, the only way to adjust it was to move the entire camera.

 
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Guest
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      07-12-2007
In article <120720070939012348%(E-Mail Removed)>, http://www.velocityreviews.com/forums/(E-Mail Removed) says...
> In article <(E-Mail Removed)> , Rob Morley
> <(E-Mail Removed)> wrote:
>
> > It seems to me that he /did/ describe a circular polariser, and then
> > added "It is NOT to be confused with the current circular
> > polarizer". So he's trying to find something that is functionally
> > identical to a circular polariser, yet is somehow different in a way
> > that he doesn't seem to be able to explain. Or am I missing something?

>
> I'm confused too. I read it as he was looking for a polarizer that
> darkened the sky but didn't need to be rotated to maintain the effect.
> "Circular" in the sense that it blocked all angles of polarized light
> at the same time. isn't that a neutral density filter? <GRIN>


Grossly oversimplifying, a polarizer is a bit like a set of louvers on a
vent. Light waves aligned the direction of the blades get through,
light waves that run into the blades get blocked.

Now, instead of using parallel linear blades, make your louvers out of
concentric tubing. No matter what the rotation of this filter, it has
the same effect.

(No physics flames, please. Like I said, grossly oversimplifying.)

I recall reading about this sort of filter many years ago, never saw one
in person.

--
(E-Mail Removed) is Joshua Putnam
<http://www.phred.org/~josh/>
Updated Infrared Photography Gallery:
<http://www.phred.org/~josh/photo/ir.html>
 
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Bill Funk
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      07-12-2007
On Thu, 12 Jul 2007 09:39:01 -0400, Scott Schuckert <(E-Mail Removed)>
wrote:

>In article <(E-Mail Removed)> , Rob Morley
><(E-Mail Removed)> wrote:
>
>> It seems to me that he /did/ describe a circular polariser, and then
>> added "It is NOT to be confused with the current circular
>> polarizer". So he's trying to find something that is functionally
>> identical to a circular polariser, yet is somehow different in a way
>> that he doesn't seem to be able to explain. Or am I missing something?

>
>I'm confused too. I read it as he was looking for a polarizer that
>darkened the sky but didn't need to be rotated to maintain the effect.
>"Circular" in the sense that it blocked all angles of polarized light
>at the same time. isn't that a neutral density filter? <GRIN>


I'm thinking the same thing.
A polarizer that works equaly well without being rotated doesn't make
much sense.
Possibly a graduated ND filter, graqduated towards the center?

--
THIS IS A SIG LINE; NOT TO BE TAKEN SERIOUSLY!

Al Gore's son was pulled over by police on the
San Diego Freeway Tuesday with marijuana, Valium,
Xanax and Vicodin on him. The kid never had a
chance. He got hooked on downers at an early
age listening to his father read him bedtime
stories.
 
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Joseph Miller
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      07-12-2007
(E-Mail Removed) wrote:
> In article <120720070939012348%(E-Mail Removed)>, (E-Mail Removed) says...
>
>>In article <(E-Mail Removed)> , Rob Morley
>><(E-Mail Removed)> wrote:
>>
>>
>>>It seems to me that he /did/ describe a circular polariser, and then
>>>added "It is NOT to be confused with the current circular
>>>polarizer". So he's trying to find something that is functionally
>>>identical to a circular polariser, yet is somehow different in a way
>>>that he doesn't seem to be able to explain. Or am I missing something?

>>
>>I'm confused too. I read it as he was looking for a polarizer that
>>darkened the sky but didn't need to be rotated to maintain the effect.
>>"Circular" in the sense that it blocked all angles of polarized light
>>at the same time. isn't that a neutral density filter? <GRIN>

>
>
> Grossly oversimplifying, a polarizer is a bit like a set of louvers on a
> vent. Light waves aligned the direction of the blades get through,
> light waves that run into the blades get blocked.
>
> Now, instead of using parallel linear blades, make your louvers out of
> concentric tubing. No matter what the rotation of this filter, it has
> the same effect.
>
> (No physics flames, please. Like I said, grossly oversimplifying.)
>
> I recall reading about this sort of filter many years ago, never saw one
> in person.
>

Grossly oversimplyfying, your concentric tube thingy wouldn't work at
all to produce circular polarization or any polarization. It could
produce a great deal of diffraction. You are absolutely right about one
thing. No matter how you rotate it, what it does won't change.

Joe

 
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Matt Ion
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      07-12-2007
Joseph Miller wrote:
> (E-Mail Removed) wrote:
>> In article <120720070939012348%(E-Mail Removed)>, (E-Mail Removed) says...
>>
>>> In article <(E-Mail Removed)> , Rob Morley
>>> <(E-Mail Removed)> wrote:
>>>
>>>
>>>> It seems to me that he /did/ describe a circular polariser, and then
>>>> added "It is NOT to be confused with the current circular
>>>> polarizer". So he's trying to find something that is functionally
>>>> identical to a circular polariser, yet is somehow different in a way
>>>> that he doesn't seem to be able to explain. Or am I missing something?
>>>
>>> I'm confused too. I read it as he was looking for a polarizer that
>>> darkened the sky but didn't need to be rotated to maintain the effect.
>>> "Circular" in the sense that it blocked all angles of polarized light
>>> at the same time. isn't that a neutral density filter? <GRIN>

>>
>>
>> Grossly oversimplifying, a polarizer is a bit like a set of louvers on
>> a vent. Light waves aligned the direction of the blades get through,
>> light waves that run into the blades get blocked.
>> Now, instead of using parallel linear blades, make your louvers out of
>> concentric tubing. No matter what the rotation of this filter, it has
>> the same effect.
>> (No physics flames, please. Like I said, grossly oversimplifying.)
>>
>> I recall reading about this sort of filter many years ago, never saw
>> one in person.

> Grossly oversimplyfying, your concentric tube thingy wouldn't work at
> all to produce circular polarization or any polarization. It could
> produce a great deal of diffraction. You are absolutely right about one
> thing. No matter how you rotate it, what it does won't change.


I think a better description would be to take the louvers, cut them in
half, and arrange them in a star shape. Any horizontally-polarized
light to the sides of the FOV would be passed; to the top and bottom it
would be blocked.

I can see the thing being a design and construction nightmare, but I can
understand where it could be useful in some instances.
 
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Scott W
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      07-13-2007
Joseph Miller wrote:
> AustinMN wrote:
>> On Jul 10, 7:44 pm, Joseph Miller <(E-Mail Removed)> wrote:
>>
>>> I'm sorry, but your description doesn't seem to make sense. The light
>>> coming from normal scenes like those in sports is not circularly
>>> polarized, so a "circular polarizing filter" or filter designed to
>>> remove cilcularly polarized light wouldn't do anything.

>>
>>
>> Backwards. It would only admit circularly polarized light, blocking
>> all others.
>>
>> Austin
>>

> Sorry for the loose terminology. I should have said "do anything you
> want to do." If it only passed circularly poarized light, then in nearly
> all scenes no light would get through, since virtually none of the light
> would be circulalrly polarized.


Any electromagnetic wave can be described as a superposition of left and
right handed circularly polarized light. For most natural light you
will have the same amount of left and right handed light.

Note you can also electromagnetic wave can also be described as a
superposition of vertical and horizontal polarized light, you are just
choosing different basis functions.

Scott

 
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