Metering with Polarizer filtersgreenspun.com : LUSENET : Large format photography : One Thread
Has anyone established a good way to know in advance exactly how much exposure compensation is necessary using a polarizer at various settings?
I do not have behind the lens metering.
The thought occurred to me that I might be able to pre-caliberate a polarizer using various settings and later take it into the field.
I have access to an evenly illuminated daylight light table and a very accurate Minolta one degree spot meter. Could I take readings through the polarizer on the light table at various settings, mark the polarizer, then use it in the field. There I can work with the compensation values I previously marked.
Another question arises - would a linear polarizer fool a one degree Minalto spot meter into giving inaccurate readings or would it be best to use circular polarizer? I understand a circular polarizer is used with modern electronics.
Does anybody have any suggestions or a fast accurate way to use polarizers at various settings with a view camera that does not have electronics? Only a hand held one degree spot meter will be used.
Please contact tallltandj @aol.com
-- Thomas Ferko (email@example.com), April 05, 1998
Using different degrees of compensation for different polarizer settings may be an unnecessary level of precision. I tend to add two stops whenever the polarizer is on the camera, regardless of just where it is set, and it seems to work fine.
-- Rob Rothman (firstname.lastname@example.org), April 06, 1998.
A linear polarizer should be just fine for your uses. I also use 2 stops compensation with a polarizer. I did a test like you mentioned when I first started using a polarizer, and I measured a 1 1/3 stop difference, but this still gave me underexposed chromes. I finally got to 2 stops, and this seems just right. You only want to compensate for the neutral density portion of the polarizer. You do not usually want to compensate for the polarization, or there would be no point in using the filter in the first place. A polarizer varies the relative contrast of objects. If you adjust for the polarization, you run the risk of blowing out your highlights. Just install the filter, adjust it for the degree of polarization you want, add 2 stops for the neutral density of the polarizer, and shoot. You may want to shoot the scene using a few different ND compensations, as some polorizers may have slightly different ND values, and settle on the one that seems best. Good luck.
-- Ron Shaw (email@example.com), April 06, 1998.