Re: Circular Polarizers, A Filter You Need

"Bob Salomon" <bob_salomon@[EMAIL PROTECTED]
> wrote in message 
news:bob_salomon-2ED153.11324608082007@[EMAIL PROTECTED]
> In article <NN2dnZ1nD_DyQyTbnZ2dnUVZ_smnnZ2d@[EMAIL PROTECTED]
>,
> "Matt Clara" <hey.wood.y@[EMAIL PROTECTED]
> wrote:
>
>
>> The circular will tend to give slightly _poorer_ results, as it's 
>> designed
>> to let some polarized light through, as some camera's autofocus systems

>> (and
>> ttl metering) depends upon it to get the job done.
>>
>> --
>> www.mattclara.com
>
> No. They polarize exactly the same. All the quarter wave plate does is
> allow some light to be processed properly by the AE or the AF, or both,
> systems if your camera has a beam splitter in the optical path.
>
> There are other factors that would make one type of polarizer more
> effective then another. For instance a Kaesmann polarizer, linear or
> circular, would be marginally more effective as the foil in a Kaesmann
> is stretched tight in all directions and lies flatter then a simply
> laminated polarizer. To keep the foil stretched tight the Kaesmann has
> edge sealed glass rather then just laminated glass.
>
> A properly hard coated polarizer with a modern MC that repels dust and
> moisture while also passing up to 99.9% of the light hitting it to the
> image plane (less what the polarizer eliminates of course) like the
> Heliopan SH-PMC coated polarizers will be more effective then a coated,
> uncoated or Kaesmann polarizer due to the coatings used. As well as the
> quality of the foils used.
>
> There are several grades of polarizers for optical use in photography.
> Better polarizers use higher grades which are more color neutral and
> have less effect on resolution then cheaper foils. The less expensive
> polarizing filters may not be as effective due to the foil quality as
> well as to the coatings and glass used.
>


Damn, luminous landscape (and what I thought of as common knowledge) once 
again let's us down:

"There are two types of polarizing filters available - linear or circular.

Linear polarizers are more effective and less expensive than circular
ones. 
But circular polarizers are needed with just about any camera that has a 
through-the-lens metering system, or autofocus.

The reason for this is that both of these systems use semi-silvered
mirrors 
to siphon off some of the light coming though the lens. If that light is 
linearly polarized it renders either the metering or the autofocus 
ineffective. This means that you're going to have to buy circular
polarizers 
unless you're shooting with a pre-1970's camera, or a view camera."

--
www.mattclara.com