Polarizer Question

[VegasGeorge]

I'm confused by the language used in the instructions I've read. Most say something like, "shoot 75-105 degrees from the sun." What does that mean? If the sun is overhead, or behind you, is the polarizer useless? Is it 75-105 degrees to either side of the sun, resulting in a 210 degree maximum arc of effective coverage? I understand degrees of variation on the compass, but that's on a two dimensional plane. The sun is always "up" there somewhere, so it's a three dimensional relationship, and I don't quite get it. Does the sun's increased elevation toward mid-day have the effect of narrowing the effective arc of the polarizer? That would mean the polarizer is most effective in early morning and late afternoon light. Somehow I don't think that's it, because my polarized sunglasses seem to have the most effect in the glaring mid-day sun.

[jukas]

I'm confused by the language used in the instructions I've read. Most say something like, "shoot 75-105 degrees from the sun." What does that mean? If the sun is overhead, or behind you, is the polarizer useless? Is it 75-105 degrees to either side of the sun, resulting in a 210 degree maximum arc of effective coverage? I understand degrees of variation on the compass, but that's on a two dimensional plane. The sun is always "up" there somewhere, so it's a three dimensional relationship, and I don't quite get it. Does the sun's increased elevation toward mid-day have the effect of narrowing the effective arc of the polarizer? That would mean the polarizer is most effective in early morning and late afternoon light. Somehow I don't think that's it, because my polarized sunglasses seem to have the most effect in the glaring mid-day sun.

Polarizers are most effective when the light source is at a 90 degree angle from you. This is especially noticeable directly at mid-day because the sun is directly above you and at 90 degrees regardless of if you are facing North, South, East or West.

It can still be effective at other angles but especially with wide shots you'll see anomalies where one part of the picture if more polarized than the other (Really blue to a faded blue to almost white).

They are also great for removing glare so keep it handy for shooting sand, waterfalls, streams, etc.

[VegasGeorge]

OK, here's another example of the confusion I'm experiencing:

"An old trick for visualizing the maximum angle is to turn your index finger into a gun (like when you were a child), with your thumb pointing upward. Make as if to shoot the sun with your finger and your thumb will point toward where polarization is at its most extreme."

OK, so I stand here with my "gun" and I point my index finger at the sun. My thumb is pointing more or less up. Why would I want to be taking pictures of the sky? That's dumb!

[SkipD]

Rotate the "gun" (around your index finger's axis) while still pointing at the light source (sun or other source). Your thumb will point at a lot of different things - not just the sky.

[iwatkins]

OK, think that you can rotate the gun around fully. I.e. your thumb can rotate in a 360 degree circle but with the barrel of the gun (your index finger) still pointing at the sun. Where ever your thumb points while it does this amazing trick is the direction where you will get the most effect from the filter.

Much easier ? Stand outside with the filter fitted. Have the sun to your left or right for maximum effect. If the sun is overhead, any horizontal shooting direction will be maximum effect also.

In fact, just go and try it, you can see the effect through the viewfinder no problem.

Cheers

Ian

[VegasGeorge]

OK, the dumb guy gets it! :lol: Finally! I guess I'm just too literal. Thanks for all your help!!!

[robertwgross]

You can look at this another way.

If the sun is low in the western sky, then it is shining toward east. If I aim the camera north or south, I should be able to turn the polarizer and get a maximum effect.

If the sun is high in the overhead sky, then directions don't help much, because most compass directions are 90 degrees away from the sun light direction (which is down). In this case, the polarizer can help some in several directions.

Where a polarizer will not help much at all is shooting directly toward the sun or directly away from the sun, unless you are simply using it as a neutral density filter.

---Bob Gross---

[RAitch]

Polarization lenses stop light that is vibrating in a certain direction.
Linear polarizer lenses are composed of several microscopic parallel lines. As light reflects off of a surface the light waves change.

As sunlight leaves the sun, it's vibrating in all directions. When it hits a windshield of a car (for example), it then will only appear to vibrate horizontally. The light that vibrates vertically won't appear to be vibrating any more. (this is hard to explain)

Since reflective light only vibrates in one direction, you can easily filter it. If you align a polarization lens so that the grooves are parallel with the light waves, they will make it through. If you turn the polarization lens perpendicular to the waves, they won't be able to vibrate through and will be reflected away (you won't see that light). That's why if you take 2 linear polarization lenses, and overlap them... you'll end up not seeing ANY light at some point. (when the grooves of one lens are horizontal and the other is vertical). At this point, there are no big holes for the light to get through)

So, think of billiards. You can bounce a ball off the rail in several different ways. Not every bounce is 90 degrees. Light reflects similarily. If light is reflecting in your direction (reflects everywhere off a sphere) you can filter it with a polarization lens.

Your subject doesn't have to form a 90 degree angle between you and the sun... unless the surface on the subject reflects light in that direction.

You can apply the same concepts to circular polarizers. Linear polarizers can be more flexible as you choose the angle of light to filter.

I hope that makes sense... although I think it might be confusing.