Re: Which Polarizer?



Roger wrote:

I have a Canon XT with a Sigma DC 18-200mm 1:3.5-6.3 lens, so obviously
I'm not a Pro!
However I'm trying to decide on a circular polarizer filter for enhancing
sky colors and minimizing reflections.
I hear that circular filters can knock 2 f-stops off a lens. Since I
already have a slow lens, would a more expensive filter take less of a
toll than a cheap one? What are the considerations? Any recommendations?

Roger


Polarizers do take about 2 stops compensation. Light from the subject
is randomly polarized, and the filter passes only the light that happens
to be in the same polarization plane as the filter, so about 75% of the
light from the subject is rejected. There is also a small further
transmission loss from the polarizing medium iself, so there's your 2
stops. There can be variations due to the 'tightness' of the
polarization, and the transmission characteristics, and with cheaper
filters there can be some color shift as well. Get the best you can
afford.

Colin D.

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