The Order of Stacked Filters

[Mark Stahlke]

Greetings,

I was looking into polarizer options for the Lee filter system. I found the answers I needed in the LFPhoto.info archives. While I was reading old message threads, I ran into a number of comments that said when stacking filters a polarizer should be first in the light path (farthest from the lens). Now I'm lying awake at night wracking my brain trying to think up a reason why that would be so. Could some kind soul spare a clue for the clueless?

Thanks,
Mark Stahlke
Charter Member of The Royal Order of Stacked Filters

[Michael S. Briggs]

Plastic, if stressed or carrying internal stress, will show interesting colored patterns if observed between two sheets of crossed polarizing material. Sometimes natural light is already partially polarized, in which case you would get this effect with only one polarizier behind the plastic. You probably don't want interesting colored patterns added to your photograph, so this isn't a good idea.

Here's a link with attractive photos of the effect: http://www.muellerworld.com/exhibits/polarized_light_macro/

[Ralph W. Lambrecht]

Mike

How is this an answer to the question? Please elaborate on why the polarizer first.

[Alan Davenport]

Mike

How is this an answer to the question? Please elaborate on why the polarizer first.

I thought Mike's answer was pretty clear. With so many of today's filters being made of plastic resins, there's a good chance that you'd see the rainbow effect if you placed one of them ahead of the polarizer. Also, internal reflections in filters (i.e., flare) is probably going to polarize that portion of the light (even in glass filters,) so putting the polarizer first will reduce the chances of unexpected rewards.

[Michael S. Briggs]

Here is a better explanation from http://www.ptonline.com/articles/200512fa2.html:

"When polarized light passes through transparent or translucent plastic, the components of the light wave that are parallel and perpendicular to the direction of the stress propagate through the plastic at different speeds. This effect is known as “retardation” and is proportional to the degree of stress in the material at that point. When light that has experienced retardation is viewed with a polariscope, the two components of the original light beam interfere with one another, resulting in a visible display of varying colors and intensities (fringes) wherever stress is present in the material."

Normally to get a good view of the effect you need two polarizers, one in front of the plastic sample to produce polarized light, and one behind the plastic sample to select the modified light. But if the incident light is already polarized, then you only need one polarizing filter, i.e., behind the plastic sample. Since sometimes natural light such as skylight is partially polarized, this one filter case can apply to regular photography. So if you want to avoid this effect you should avoid placing a polarizing filter behind a plastic filter. In other words, place a polarizing filter in front of a plastic filter. Then there won't be a polarizing filter in a position to select which portions of the light have been retarded so as to show colorful interference effects.

[Mark Stahlke]

Thank you, Michael. I knew there had to be a reason, I just couldn't imagine what it was. I've seen photos of polarized plastic and they are quite interesting but I'm sure I don't want that effect in my landscapes.

Thanks, again. Now I can sleep at night.

[Ralph W. Lambrecht]

I thought Mike's answer was pretty clear. With so many of today's filters being made of plastic resins, there's a good chance that you'd see the rainbow effect if you placed one of them ahead of the polarizer. Also, internal reflections in filters (i.e., flare) is probably going to polarize that portion of the light (even in glass filters,) so putting the polarizer first will reduce the chances of unexpected rewards.

Thanks. Now I understand! My confusion came from not using plastic filters myself.

[Joanna Carter]

Thanks. Now I understand! My confusion came from not using plastic filters myself.
I was advised, by an optical engineer, to place the polariser closest to the lens because it means that any deviations caused by filters in front will be cancelled instead of allowing filters behind the polariser to introduce deviations.

[Bob Salomon]

On what focal length lens?

[Petewit]

Cokin system puts polarizer closest to the lens and the Lee system furthest from the lens. Both use resin filters. You takes your choice.