[LargeFormat] polarizer compensation

[Clive Warren]

At 08:25 12/11/2002 -0800, Jim Brick wrote:
>My Gossen meters (Luna Star F2 & Luna Pro Digital) will take a reference 
>reading through filters and set their internal offset to the value that 
>they saw reading through the filters. I have always used this method and 
>it seems to be spot on for my purposes.
>
>I recently was using ISO 100 film (Provia 100F) and wanted to get down to 
>several seconds exposure (silky water,) out in the bright sun. I used a 
>1.8 ND (6 stops) and a polarizer (~2.5 stops). I read the two through my 
>meter to set the offset. Then read the scene and got 4 sec at f/32, which 
>was the correct exposure. I bracketed + and -, but the indicated meter 
>exposure was the correct exposure.
>
>Jim
>
>
>At 06:30 PM 11/11/2002 -0800, Brock Nanson wrote:
>>Here's a quick one that will undoubtedly bring a variety of responses!!
>>What do people use for a typical exposure compensation for a Polarizing
>>filter?  I've seen 1.5 to 2 and a bit stops... I've always gone with 2 but
>>wonder if 1.5 might brighten the shadow somewhat, without lightening the sky
>>too much.  Is there a difference between circular and linear w.r.t. neutral
>>density?
snip

I use the same approach as Jim to measure filter factors accurately for the 
range of filters in the kit bag - ie use a meter. In this case it's a 
Pentax analogue spot meter pointed at a suitably large patch of something 
with a fairly consistent reflectivity. The polariser I use is about 2 stops 
and the #25 red filter is between 1.5 and 2 stops. There is no real 
difference between a circular and a linear polariser wrt the filter factor 
- although different manufacturers will probably have an effect. You don't 
need a circular polariser for large format cameras - which should save you 
a bit of money!

Cheers,
            Clive