Re: [OM] Help! Light theory, cp-l

[dreammoose]

In theory, a CPL filter first filters out light based on its polarity 
and then 'un-polarizes' what came through. I just tried looking through 
2 CPLs and find that rotating one does slightly change the density and, 
perhaps more importantly, causes some color changes at certain angles. 
I assume this is because the un-polarizing is slightly imperfect. 
Further, I believe the un-ploarizing can be either clockwise or CCW and 
don't know which the 2 filters I happen to have are, so results with 
other filters could vary. The color tinting with my filters is strong 
enough that I wouldn't use them in combination.
Moose

Mickey Trageser wrote:

> Those of you who are familiar with the light theory regarding linear
> polarizers may be able to answer this. Aside from possible vignetting, what
> is the effect of stacking 2 CP-L filters? Is is simply adding to the
> density, or does it affect the polarizing quality? Also, if I use the 1 or 2
> CP-L filters as neutral density with flash, how do I compensate the flash
> meter reading? My subject may not be appropriate for TTL flash control.

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