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Photography Question 
Debra L. E.
 

Characteristics of a Circular Polarizing Filter


I recently purchased a Hoya circular polarizing filter. While hand-holding the filter, should I be able to see the difference in color as I turn it? It looks like a clear piece of glass to me. My pics with it do not seem affected either. Thank you for your help over the last couple of years. Thanks to you guys, my husband saw an answer you had given me about camera choices, and a few months later, he upgraded me to a Nikon D80. I am a happy woman!


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4/15/2008 2:22:31 AM

 
Bob Cammarata
BetterPhoto Member Since: 7/17/2003
cammphoto.com
  Your eyes and brain "correct" the effect, but you still should be able to see the difference when you turn the ring while looking through the viewfinder. You can also watch the TTL metering system in your camera adjust when you turn the ring.


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4/15/2008 3:51:45 AM

 
Ken Smith
BetterPhoto Member Since: 6/11/2005
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  Find a reflection in a window ... as you rotate the polarizer, you should see the reflection disappear, or at least be reduced. Same for water. And if the sky is blue, you should see it deepen. It's very visible. When you say "turn it", are you simply holding the polarizer in your hand, without the camera? Or is it screwed onto your lens, and you're turning the outer ring? It sounds like you have a straight ND filter, but I doubt that's the case.


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4/15/2008 4:04:30 AM

 
Debra L. E.   Thanks, Bob C. and Ken S.. I have held the filter in my hand looking at the sky through the filter. And I have taken pictures in sucession, rotating the filter 1/4 turn, I see no difference. As it was dark when I arrived home I could not try your suggestion with the sky. ( I will tomorrow, though) I also looked at the monitor while rotating the outer ring and the camera did not change the settings. Is there a circular ND filter? I bought this filter online and was shocked when I could not see any difference when I have read many photography facts that tout the darking of the blue in the sky snd the reflective surfaces. Again thanks for your responses.


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4/15/2008 6:12:41 PM

 
Ken Smith
BetterPhoto Member Since: 6/11/2005
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  I've never heard of a circular ND filter. You can do a google search on circular polarizers; e.g., http://www.offrench.net/photos/articles/polarizing_filter.php

You might take your camera and the filter into a reputable camera store and have someone knowledgeable on polarizers check yours out...

How much did you pay? The good ones can cost upwards of $100.


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4/15/2008 7:01:19 PM

 
Oliver Anderson
BetterPhoto Member Since: 11/16/2004
  Debra, I'm thinking it was too dark to see so wait till morning. I just grabbed a couple of mine and in the dark without lights on I couldn't see anything.lol


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4/15/2008 8:57:46 PM

 
Gregory LaGrange
BetterPhoto Member Since: 11/11/2003
gregorylagrange.org
  You can look at your bathroom faucet.


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4/15/2008 9:33:01 PM

 

BetterPhoto Member
  It'll work with the mirror. Anything except metal. Polarizers have no effect on reflections on metal.


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4/17/2008 3:42:33 PM

 
Debra L. E.   Thaks agin for all your help. I have determined that I have a "cheap" filter. I only paid around $40 for it...I thought by buying the brand name, the cheap price would not lessen the quality. I have tried all the numerous test you gave and there is no difference. Thanks again for helping me to leearna valuable lesson in buying cheap equipment.


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4/18/2008 2:23:19 AM

 
Gregory LaGrange
BetterPhoto Member Since: 11/11/2003
gregorylagrange.org
  I thought Hoya was a good brand. Maybe you got a packaging mistake.
Does it say CPL along the rim of it?


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4/18/2008 5:49:57 AM

 
Oliver Anderson
BetterPhoto Member Since: 11/16/2004
  Heliopan or B&W are high quality filters. Never understood spending $2,000 on a lens and trying to save $40 on a filter to cover the expensive glass.


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4/18/2008 8:53:02 AM

 
Denny E. Barnes
BetterPhoto Member Since: 1/19/2008
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  Debra, There is a quick check for how good a polarizing lens is. If you know someone who has a good lens or good polarizing sunglasses, hold them together and turn one, at some point if they are good lens you should not be able to see through them or very little. They work by passing light at one angle only so when they are at 90° to each other no light can pass. Reflected light that is at a different angle is stopped, this is how they work. Polarize-rs at times do not appear to work because there is very little reflected or scattered light to stop. My lens is a $40 SUNPAK and it works very well. Also a camera shop can tell you very quickly if the lens is any good. Hope this might be of some help.
Denny


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4/18/2008 9:31:02 AM

 
Debra L. E.   Again, thanks. Gregory, on the rim of the filter reads HOYA 62mm PL-CIR. Denny, thanks so much for your excellent description of how the filter works. I truly understand now why walking around the house in the evening would not have shown me any difference. This site always has friendly people who are so willing to help amateurs on limited budgets. I confess to being both. But, thank goodness their are people like you around for us!


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4/19/2008 10:30:32 AM

 
Ken Smith
BetterPhoto Member Since: 6/11/2005
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  Debra, I can't tell from all your posts, if you have actually screwed the filter onto your camera, then rotated it to see how it does with a water reflection, or window reflection, or even a blue sky. The polarizer is definitely suited for daytime photography. From what's written on the filter, it sure sounds like a polarizer.


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4/19/2008 10:58:55 AM

 
Alexander    I was always given to understand that the polarizer only really worked when the sun or light was at 90 degrees to you. As in, to the side and not in front or behind you.


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4/22/2008 5:12:56 AM

 
Steve Parrott
LightAnon.com
  Alexander finally gave you a bottom line answer. A polarizer does NOT have an effect at all times. It is only effective when you are in certain relative positions with the sun. You can certainly hold the filter in front of your eyes and see the effect. You do not have to have it mounted on the camera. If the sun and your position are correct, you will see a dramatic effect of darkening of the sky and elimination of reflections. Sometimes just turning your body 90 degrees can make a huge difference as to the effect of the filter. I actually have a small Kinko circular polarizer filter that mounts into my flash hot shoe. I can take a quick look with it to see if there is a need to mount a filter on the camera or not.
steve


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4/22/2008 7:24:56 AM

 
Alan N. Marcus   The polarizing filter (correct is polarizing screen) is the most useful filter available. 1. It darkens blue sky thus causing clouds to stand out. 2. It reduces reflections. 3. Penetrates haze. 4. Acts as a natural density filter.

To understand how it works: As water waves travel (direction) the waves undulate only in an up and down direction (plane of vibration). Light waves undulate also however they are not restricted to any single direction. Light wave undulate in all planes, up-down, left-right, diagonally, in fact every possible angle. This is the nature of unpolarized light.

In 1669 it was observed that a view through a crystal of calcium carbonate produced a double image. In 1808 it was observed that reflections from a glass window did not split off into two images. Augustin Frresnel in 1814 explained the how and why. In 1930 Edwin Land produced polarizing filters by embedding microscopic crystals into sheets of plastic.

The filter acts as if it is ruled with dark lines all running in the same direction spaced very close together. When light rays transit the filter, only these rays that vibrate in line with the rulings can pass. All other rays are blocked. This action is like kids holding a jump rope passing it through a missing picket in a fence. They can pluck the rope up and down and it vibrates freely but if they pluck it sideways it collides with a picket on left or right and the vibration is dampened.

Light is normally unpolarized. When a light ray hits something it is likely reflected and reflected light is likely polarized meaning its rays undulate in only one plane (direction). This is true only if the reflecting surface is a dielectric (nonconductor of electricity). Most metals are conductors so polarizing screens don’t work on them. However many metals are painted or have a natural protective coat of transparent oxide which is a dielectric. Pond water with low mineral content is a poor conductor as is glass and painted surfaces are dielectrics thus the polarizer works on many substances.

The maximum darkening effect on sky occurs when taking a picture at right angles to the sun. For maximum effect, you must have the ability to rotate the filer about its axis as you observe. This is true because the filter screens out all but one plane of vibration and the plane you need to allow to transverse is a variable.

Many cameras use polarizing filters inside their auto-focus and auto-exposure optical path. For these models, a polarizing filter interferes and causes havoc. The circular polarizer is two filters sandwiched together. The first does the polarization rejecting rays except those vibrating in just one plane. Now that the job is done, the second filter scrabbles and thus unpolarizes the light that is presented to the camera lens. This action allows the camera to operate normally while still getting full benefit from the polarizing screen.

Alan Marcus (marginal technical gobbledygook)
ammarcus@earthlink.net


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4/22/2008 8:43:39 AM

 
Oliver Anderson
BetterPhoto Member Since: 11/16/2004
  Alan...did you have to research that or is it in that head already???? You should be teaching over at UCI.


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4/22/2008 10:14:14 AM

 
Alan N. Marcus   Thanks Oliver A.

In addition to my regular duties, I taught color print and process for many years at the PPA (professional Photographers of America) summer school for continuing education Winona. In my youth I went through a formal apprenticeship as a photo engineer. I was also schooled at Kodak’s MEC and I was granted a license by Kodak to operate under their patens and applications pertaining to color films. I practiced as a photo engineer until I retired 5 years ago. I am now 70 years old. I have never stopped learning or teaching. When I die a pile of photo trivia will surly be left behind. Someone please sweep it under a large automated film developing machine.

Alan Marcus (marginal technical stuff)
ammarcus@earthlink.net


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4/22/2008 10:50:16 AM

 
Carlton Ward
BetterPhoto Member Since: 12/13/2005
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carltonwardphoto.com
  Alan, I always appreciate your detailed explanations and I learn a lot from your posts. Maybe you could set up a database for your "pile of trivia". Maybe BetterPhoto could even set up a Alan Marcus Gobbledygook page?

Thanks again Alan


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4/22/2008 11:34:37 AM

 
Gregory LaGrange
BetterPhoto Member Since: 11/11/2003
gregorylagrange.org
  Ken Smith gave her a bottom line answer.


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4/22/2008 3:29:55 PM

 
Oliver Anderson
BetterPhoto Member Since: 11/16/2004
  Ken's got some great photos too so my vote got to Ken, but Alan for Technical knowledge.


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4/23/2008 2:35:26 AM

 
Dennis Creaghan   It's rather a simple point but no one has mentioned it so I will; remember that the polorizer is most effective 90 degrees from the sun, the closer you turn towards the sun the less polorization effect. Facing directly towards the sun, no effect at all!

Dennis


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4/23/2008 1:33:22 PM

 
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