Exposure factor of B&W PL?greenspun.com : LUSENET : Large format photography : One Thread
Recently I got a B&W PL, but I could not find anything about exposure factor on the box, and they didn't print it on the ring. Anybody can get me tips? Thank you.
-- max (firstname.lastname@example.org), March 05, 2001
What is a B&W PL? Pat
-- pat krentz (email@example.com), March 06, 2001.
I'm going to guess this is a polarizer. If so, you might start at 1-2/ 3 to 2 stops. I suppose you could also meter through it at a flat target like a grey card.
-- Robert A. Zeichner (firstname.lastname@example.org), March 06, 2001.
I expect it's a B&W manufactured linear polariser you're referring to.
I'd go with the above, 1.5 to 2 stops, but it really depends on how much polarised light is reflecting from the subject. Stick it over your meter or take a TTL reading.
-- Pete Andrews (email@example.com), March 06, 2001.
Pete's statement that the factor depends on the amount of polarized light sounds logical but I believe it is incorrect. The factor is the same regardless of the amount of polarized light. See, e.g., Adams, "The Camera," p. 169. "The filter factor for a polarizer is usually 2.5; it is not correct to assume that the exposure factor increases as the amount of polarization increases, since this would result in overexposure of the non-polarized areas."
-- Brian Ellis (firstname.lastname@example.org), March 06, 2001.
I use a polarizer quite a bit and I allow 2.5 stops for it. I shoot 4x5 transparencies and that factor is right most always. you can meter through it if you want to be sure.
-- Erik Gould (email@example.com), March 06, 2001.