Circular Polarizer - How it works

[Abel]

well sorta... I just read this last night in my new Outdoor Photographer Mar 2005

"Polarizers can darken a blue sky (but only at certain angles to the sun). What they're actually doing is cutting the glare from moisture and dust particles from the atmosphere"

i always wondered how it made the sky darker... i knew they reduced glare on water surfaces and wondows etc etc.

[cbuhay]

I think of a polarizer as a micro screen that only allow light waves that are horizontal (in the same plane) to the screen to go through it.

For polarizers to work most effectively, the angle of polarization must be perpendicular to the llight striking the filter -- that is why your circular polarizer is turnable.

The next time you have a polarizer on your lens, point it towards the sky, and slowly turn your polarizer, you will notice that as it spins, the sky will get darker and lighter. Where the sky is at it's darkest is the angle that the polarizer is perpendicular to the light striking it.

-christian.

[Manny]

you and the lens need to be at an angle of about 90 degrees. It may work at less of an angle, I've had them do the job for me that way but you do not want it directly infront of you or behind you.
as you rotate the filter you'll see that every 90 degrees you get the different blues and greens.

[Sideline]

As long as I get my dark blue sky, I don't worry about angles and planes :)

[Abel]

hehe.. i knew how they worked and such but never put 2 and 2 together to figure out why the sky got darker etc...

now i know. hehee

[Bill Huber]

The thing of it is, they are not just to make the sky darker.
They also work as an NDF and will work in other then sun light.

One good place it use them is when you are shooting in shop windows and the like, they will kill the reflection, but you must rotate them to see at what point the reflection is gone.

I just about never go out side with out it, it can make so much difference in the colors of things. Take a flower, with a polarizer you can have a much softer look, but still be a very sharp image.
You can also use them inside to kill reflections from the lights in side, it makes a big difference in some images.

One place you really can not use them is shooting though a car window. You will get some funny looking dark areas in the the shot.


Here are just a few ways they can help you.
http://www.pbase.com/otfchallenge/use_of_polarizer_lens

[cbuhay]

Originally Posted by Bill Huber

One good place it use them is when you are shooting in shop windows and the like, they will kill the reflection, but you must rotate them to see at what point the reflection is gone.

yep... I used a polarizer at the zoo meet, and that's how I cut through most of the glare in the reptile house.

[jeffkohn]

Only downside you have to be aware of is you're losing as much as 2 stops of light, which can cause problems if your shutter speed is borderline to begin with. (That's why polarizers can be used as ND filters in a pinch).

[wedeking]

A word of caution:

If you are shooting a panorama and planning on stitching the shots together you might want to avoid polarizers.

Its been my experience that CP's don't uniformly deepen/darken the sky across the frame, especially in wide angle shots. I'm assuming that this is due to the 90 degree requirement mentioned above. So when you stitch the shots together, you can see the difference in the sky from frame to frame.

Of course, it could just be user error. :)

Greg

[Bill Huber]

Originally Posted by wedeking

A word of caution:

If you are shooting a panorama and planning on stitching the shots together you might want to avoid polarizers.

Its been my experience that CP's don't uniformly deepen/darken the sky across the frame, especially in wide angle shots. I'm assuming that this is due to the 90 degree requirement mentioned above. So when you stitch the shots together, you can see the difference in the sky from frame to frame.

Of course, it could just be user error. :)

Greg

You should NEVER use a polarizer filter when taking panos, it just will not work, you will never get the sky to be the same color in each shot. The angle of the light changes as you move the camera for the next shot.