Re: [ATM] [Fwd: Re: Betr.: Re: cutting a big piece of plate glass - Polarizer]

[George Anderson <tillerman1@videotron.ca>]

Circular polarizers consist of a linear polarizer bonded to a 1/4 wave 
retarder, this creates the circular polarization. It is either right 
handed or left handed depending on how it is bonded to the retarder 
plate. There are some sheet film linear polarizers but I do not believe 
that they are of true "optical" quality (photographic or visual). Then 
neither were the IR sheet polarizers that I bought from Polaroid for work.
Digital cameras get very confused (both metering and autofocus) with 
linear polarizers.

George Anderson
Montreal Canada

Clear skies and good health

Jeff Rowe wrote:
> Friends;
> Prior to ~20 years ago 99% of all camera polarizer filters were linear. 
> Yea!!! I believe the change to "circular" came about due to the meter 
> sensors in SLRs. I have a pile of both and much prefer the linear. They 
> are very out of vogue, there might be issues with digital chips as well. 
> Take one of each and visually look to a north blue sky and compare. The 
> linear is much more "aggressive", the "circular"  doesn't confuse the 
> metering in modern cameras. I have not seen large circular gells yet, 
> and for that matter really don't see the point.  I believe all stress 
> tests should be done with linear polarizers. When you rotate one to the 
> other you begin to see stress etc. When 2 linear polarizers are at 90* 
> you tend to null toward opaque, because they are not 100% efficient, you 
> often have a very dark blue result. I have not found this to be the case 
> when using PL-CIR.  IMHO they were a lousy kluge to deal with metering 
> sensors, auto focus and the like.
> Cheers
> JR
>
>   
>> DLW> I never found one that was purely 2 linear polarizers.
>>
>> OK, having dredged the deeper darker brain cells, I recall circular
>> polarisers are used in photography, as are linear.
>>
>> No, they are not two linear polarisers, they are just one linear
>> polariser or one circular polariser. The purpose is not to act as a
>> variable neutral density filter, it is to act as a filter to
>> selectively block out strongly polarised light, like sunlight
>> reflected off water for example. If the filter is marked PL it is
>> linear polarised and if it is marked PL-CIR it is circularly
>> polarised. Both have there uses, but I believe one is better for auto
>> focus and one is better for manual focus camera, and no, I can't
>> remember which. Never seen a pair in one cell though Dominic.
>>
>>  
>>
>>     
>
>
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