Metering when using a polarizergreenspun.com : LUSENET : Large format photography : One Thread
I'd like to hear some technique tips for metering when using a polarizer. I have a Wista DX II 4x5 Field and I am using the Cokin P Series holder and a Cokin Circular Polarizer. I use a Minolta Spot F for my meter. I have experimented with hand holding the polarizer in the desired orientation and metering through it with the spot meter, calculating my desired exposure, and then placing the filter in the holder in the same orientation before exposing. Is this the preferred method of you, more experienced, LF users? Or is there an easier way to do this? I am getting very inconsistent results and it is getting a little frustrating. Thanks for your thoughts, -Scott.
-- Scott Bacon (email@example.com), June 22, 2000
See this - http://www.photo.net/bboard/q-and-a-fetch-msg.tcl? msg_id=000O2O&topic_id=23&topic=photo%2enet
-- sheldon hambrick (firstname.lastname@example.org), June 22, 2000.
Everything I have read including Tiffen's sheets, specifies a straight 2 stop exposure increase for polarizers, regardless of the setting. I think you should probably be using a standard linear polarizer for your setup. As I understand, the circular is for auto focussing cameras.
-- Tony Brent (email@example.com), June 22, 2000.
Although I have a hand-held meter, I usually meter with a 35mm camera with the same filter as the one use on the LF camera.
-- Q.-Tuan Luong (firstname.lastname@example.org), June 22, 2000.
I found that a 2 stop correction works best for me. You can use either linear or circular.
-- Ron Shaw (email@example.com), June 22, 2000.
I belive the compensation for a polarizer should be fixed regardless of orientation. I just meter the scene w/ no filter, compensate a fixed amount for the polarizer (1 2/3 stops for a B+W kaseman), and shoot.
-- James Chow (firstname.lastname@example.org), June 22, 2000.
The orientation of a polarizer is immaterial as no matter how much you turn it its density remains constant. If the density of the filter remains constant so does the exposure factor.
-- Bob Salomon (email@example.com), June 22, 2000.
This is an interesting question since I love using polarizer. I use Luong method to cross check, and I use Ron's to measure. I check my polarizer with my spotmeter and found that at max. the compensation is 1 2/3 but 2x is on the ring. Since I have the tendency to overex a bit and underdevelop a bit, I compensate for 2x. Sometimes, in a hurry I just hold the filter flat against my spotmeter and shoot, it worked.
-- dan nguyen (firstname.lastname@example.org), June 22, 2000.
I started off using the 2 stop adjustment for my polarizing filter but it still seemed a bit underexposed so I now compensate by 2 1/2 stops. The best answer may be to test your own filter and shoot a variety of exposures to see what is most accurate. You might want to do this using a 35mm camera to save the large format film costs - whatever factor you come up with for the filter should work with all films.
FWIW, Ansel Adams ("The Negative", page 114) says "Because of the change in values as the polarizer is rotated, photographers frequently assume the exposure factor must be increased as the degree of polarization increases. This is not the case! When used at the non-polarizing angle, the polarizer acts a neutral density filter with a factor of 2.5; at maximum polarization the same factor applies. If we increased the factor as the degree of polarization increased, the non-polarized areas would be overexposed. The same factor applies regardless of the film or the light source."
-- Bruce Pollock (email@example.com), June 22, 2000.
It is correct to say that the density of the polarizing filter is independent of the angle of rotation so long as the illumination is is not polarized. However, the polarizer is often used to "darken" the sky. It is effective because the light from the sky is partially polarized (depending of the angle between the sun and the sky in the frame). In light of this (no pun intended!) and in order to get a complete view of the effect of the filter on the scene I turn the polarizer to the desired angle, note its orientation and meter through it. When I'm ready I screw the polarizer onto the lens and adjust the rotation. Works for me, but its just one of the ways to do it. Dave
-- David Lewis (firstname.lastname@example.org), June 27, 2000.