Linear polarizer that turns

[kenj8246]

I don't know why, but I wasn't expecting this linear polarizer to turn. Why does it do that? I was laboring under the impression that circular polarizers tuned and linears didn't. Is this functionality something I should be able to see on the GG? Do I even care that it turns? Admittedly, I don't know what I'm doing. :confused: Appreciate any insights.

Kenny

[Emmanuel BIGLER]

I don't know why, but I wasn't expecting this linear polarizer to turn.

Hi !

"Linear" or "Circular" do not refer to any movement of the filter itself, but to the design of the polarizing filter.
Hence both types of polarizers should have a rotating ring independant from the threaded ring mount.
Both kinds of polarizing filters are supposed to act on totally or partially polarized light.
A "circular" polarizing filter is a stack of two optical components, a linear polarizer and a quarter-wave plate. The quarter-wave plate transforms linearly polarized light into circularly polarized light in order to avoid unwanted cut-off effects in TTL exposure meters inside reflex cameras.

For view cameras, a circular polarizing filter is not useful, but for sure you have to rotate the mount of either linear or circular polarizing filters in order to see any effect!
Classical effects of a polarizing filter are
1/ suppressing unwanted reflections on water or glass or plastic; nothing happens with metallic surfaces;
2/ darkening a blue sky: the effect is most effective when the sun is shining at 90° from the optical axis of the camera.

In both cases and both types of polarizing filters you have to rotate the setting ring and see what happens.

[cowanw]

It won't do anything if there is no polarized light to work on. But, if you do have polarized light, say, reflections on water, then turning the filter strengthens or weakens the effect; same as for a circular polarizer. While admittedly confusing to understand the theory of the two types, they do not differ in functionality for LF mostly.
Here's something to educate yourself
http://en.wikipedia.org/wiki/Polarizing_filter_(photography)

[kenj8246]

I don't know why, but I wasn't expecting this linear polarizer to turn.

Hi !

"Linear" or "Circular" do not refer to any movement of the filter itself, but to the design of the polarizing filter.
Hence both types of polarizers should have a rotating ring independant from the threaded ring mount.
Both kinds of polarizing filters are supposed to act on totally or partially polarized light.
A "circular" polarizing filter is a stack of two optical components, a linear polarizer and a quarter-wave plate. The quarter-wave plate transforms linearly polarized light into circularly polarized light in order to avoid unwanted cut-off effects in TTL exposure meters inside reflex cameras.

For view cameras, a circular polarizing filter is not useful, but for sure you have to rotate the mount of either linear or circular polarizing filters in order to see any effect!
Classical effects of a polarizing filter are
1/ suppressing unwanted reflections on water or glass or plastic; nothing happens with metallic surfaces;
2/ darkening a blue sky: the effect is most effective when the sun is shining at 90° from the optical axis of the camera.

In both cases and both types of polarizing filters you have to rotate the setting ring and see what happens.


It won't do anything if there is no polarized light to work on. But, if you do have polarized light, say, reflections on water, then turning the filter strengthens or weakens the effect; same as for a circular polarizer. While admittedly confusing to understand the theory of the two types, they do not differ in functionality for LF mostly.
Here's something to educate yourself
http://en.wikipedia.org/wiki/Polarizing_filter_(photography)

Thank you both. I'm painfully aware of needing to experiment more. I'll take a stab and say that when the sun is overhead, or nearly so, is one time, at least, that the sun is shining at 90 degrees from camera axis?

Kenny

[Jac@stafford.net]

Viewing the scene on a ground glass through a polarizing filter can be difficult. I'm an old rangefinder user and find it easier to look through the polarizer above the camera, note the position and then place it over the lens before exposure.
.

[kenj8246]

Viewing the scene on a ground glass through a polarizing filter can be difficult. I'm an old rangefinder user and find it easier to look through the polarizer above the camera, note the position and then place it over the lens before exposure.
.

I'll certainly give that a try. My eyes are old, the rest of me thinks I'm still 25 sometimes. :)

Kenny

[Emmanuel BIGLER]

I'll take a stab and say that when the sun is overhead, or nearly so, is one time, at least, that the sun is shining at 90 degrees from camera axis?

Yes, but in countries like France where I live, latitudes around 45°, the sun is hardly ever higher than 60° above you. In the US South West, at 30° of latitude, the sun can climb higher, up to 83° in principle, in summer.

More common in landscape photography is when the setting sun is just above the horizon in the direction of the West, and if you look at distant mountains located South, or North.
In this situation, the polarizer properly set efficiently cuts-off scattered light and enhances the contrast of distant mountains.

[Maris Rusis]

Here's a rule of thumb I use to find the area in the sky where the polarizer works most strongly: point your index finger at the sun while holding your thumb straight out. Now rotate your wrist keeping the index finger directed at the sun. Your thumb points out the band in the sky of maximum polarization.

[Emmanuel BIGLER]

a rule of thumb I use to find the area in the sky where the polarizer works most strongly

Hello from the other side of the planet ! Yes this is an excellent rule !

And we may add : people living in Noosa, Australia ( 26° 23′ 19″ S, 153° 2′ 5.3″ E ) can enjoy to have the sun close to 90° above horizon those days while typing their message fo this truly international forum ;)