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How to use a circular polarizer ??

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fibroman

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Hi. I just picked up a circular polarizer for my 70-200mm f/4L lens, and it can be manually rotated all the way around after being fixed on the lens.
Should I rotate it, or will the autofocus somehow take care of it for me.
As you can see, I am quite confused.
 
fibroman said:
Hi. I just picked up a circular polarizer for my 70-200mm f/4L lens,
and it can be manually rotated all the way around after being fixed
on the lens.
Should I rotate it, or will the autofocus somehow take care of it for
me.
As you can see, I am quite confused.
Click to expand...
I have one that I occasionally use with my 70-200mm F2.8 non-IS. I don't see any difference when I rotate it. Hopefully someone can explain this if there is a secret to it.

cheerz
 
Yes you have to rotate it. Look through the viewfinder and rotate it. You would see a change in colour saturation, specially if the sky is included. It won't have any effect on a cloudy sky though. Polarisers work best when the lens is at 90 deg angle with the Sun. Alternatively, point the dot (or some other mark) on the polariser rim to the position of the Sun to get the maximum effect.

For details of polarised light & polarisers, see here

http://en.wikipedia.org/wiki/Polarizer

--
Gautam
 
There is a bit of an art to polarizer use. Its effect is to block polarized light, polarized light appears when light is reflected from a shiny surface or off particles in the air, for instance. The filter is directional in its effect, it will only block polarized light that is polarized in a certain plane. That is why the filter can be rotated, its position must be 90 degrees off the polarized light plane for it to work!

For a test, find a building with a window. Shouldn't be too hard. Stand outside the building, at a fairly steep angle to the window, more to the side than directly in front of it. The optimum angle is about 35 degrees off the plane of the window. The window reflection is polarized light. The polarizer will allow you to get rid of most of the reflection so that you can see into the building.

Point the lens at the window. Now rotate the polarizer. At a certain position it should magically remove the reflection. The angle off the window must be just about right for this to work! This effect means that polarizers can be used inside museums to remove reflections off glass cases - if there is enough light to use one.

The same principle applies to darkening the sky, most of the glare is reflected, polarized light and can be removed with the filter so that the sky goes dark blue. The effect is only noticeable at about ninety degrees off the sun (ie the sun should be at your shoulder, not in front of you or behind your back) and covers a relatively narrow band of sky - hence polarizers are not really suitable for this use on a wide-angle lens because the effect will be very uneven through the frame!

Reflections are also visible off leaves and other vegetation, and off the surface of water. Polarizers work there too, making vegetation colours more saturated and allowing you to "see through" the water surface. Roof-tiles and cobblestones are affected by polarizers in the same way as vegetation, to a very surprising degree! Reflections off metallic surfaces are not affected by the polarizer, however.

The polarizer can also be used as an ersatz neutral density filter, it costs about two full stops of light. You do need fairly good lighting to use it, in other words!
 
You do an excellent job of explaining the use of a polarizer. Thanks.
Staale S said:
There is a bit of an art to polarizer use. Its effect is to block
polarized light, polarized light appears when light is reflected from
a shiny surface or off particles in the air, for instance. The filter
is directional in its effect, it will only block polarized light that
is polarized in a certain plane. That is why the filter can be
rotated, its position must be 90 degrees off the polarized light
plane for it to work!

For a test, find a building with a window. Shouldn't be too hard.
Stand outside the building, at a fairly steep angle to the window,
more to the side than directly in front of it. The optimum angle is
about 35 degrees off the plane of the window. The window reflection
is polarized light. The polarizer will allow you to get rid of most
of the reflection so that you can see into the building.

Point the lens at the window. Now rotate the polarizer. At a certain
position it should magically remove the reflection. The angle off the
window must be just about right for this to work! This effect means
that polarizers can be used inside museums to remove reflections off
glass cases - if there is enough light to use one.

The same principle applies to darkening the sky, most of the glare is
reflected, polarized light and can be removed with the filter so that
the sky goes dark blue. The effect is only noticeable at about ninety
degrees off the sun (ie the sun should be at your shoulder, not in
front of you or behind your back) and covers a relatively narrow band
of sky - hence polarizers are not really suitable for this use on a
wide-angle lens because the effect will be very uneven through the
frame!

Reflections are also visible off leaves and other vegetation, and off
the surface of water. Polarizers work there too, making vegetation
colours more saturated and allowing you to "see through" the water
surface. Roof-tiles and cobblestones are affected by polarizers in
the same way as vegetation, to a very surprising degree! Reflections
off metallic surfaces are not affected by the polarizer, however.

The polarizer can also be used as an ersatz neutral density filter,
it costs about two full stops of light. You do need fairly good
lighting to use it, in other words!
Click to expand...
 
So what do you use for a wide angle lens if not a polarizer? I will be taking a lot of mountain/lake pictures at all hours of the day, but it will be with a wide angle lens, probably the canon 10-22. Any other advice?
 
With a wide angle the usual answer is "nothing", or perhaps a protective UV filter if you believe in that sort of thing. Or a graduated neutral density filter in a square filter holder, for the tripod-and-remote-release crowd.

it is not impossible by any means to use a polarizer with an ultrawide, but it does take some careful thought when shooting if you are to avoid the typical "purple band down the middle of the sky" phenomenon.
 
Polarizers are useful on wide angle lenses, too! Just be careful!

1) Be sure to get an extra thin polarizer filter to avoid vignetting.

2) Be aware of over-polarizing which produces a sky an unnaturally blue sky. With wide angle lens, the field of view may be so wide that the sky will have a large differnce in color.

-Paul
 
Staale S said:
There is a bit of an art to polarizer use. Its effect is to block
polarized light, polarized light appears when light is reflected from
a shiny surface or off particles in the air, for instance. The filter
is directional in its effect, it will only block polarized light that
is polarized in a certain plane. That is why the filter can be
rotated, its position must be 90 degrees off the polarized light
plane for it to work!

For a test, find a building with a window. Shouldn't be too hard.
Stand outside the building, at a fairly steep angle to the window,
more to the side than directly in front of it. The optimum angle is
about 35 degrees off the plane of the window. The window reflection
is polarized light. The polarizer will allow you to get rid of most
of the reflection so that you can see into the building.

Point the lens at the window. Now rotate the polarizer. At a certain
position it should magically remove the reflection. The angle off the
window must be just about right for this to work! This effect means
that polarizers can be used inside museums to remove reflections off
glass cases - if there is enough light to use one.

The same principle applies to darkening the sky, most of the glare is
reflected, polarized light and can be removed with the filter so that
the sky goes dark blue. The effect is only noticeable at about ninety
degrees off the sun (ie the sun should be at your shoulder, not in
front of you or behind your back) and covers a relatively narrow band
of sky - hence polarizers are not really suitable for this use on a
wide-angle lens because the effect will be very uneven through the
frame!

Reflections are also visible off leaves and other vegetation, and off
the surface of water. Polarizers work there too, making vegetation
colours more saturated and allowing you to "see through" the water
surface. Roof-tiles and cobblestones are affected by polarizers in
the same way as vegetation, to a very surprising degree! Reflections
off metallic surfaces are not affected by the polarizer, however.

The polarizer can also be used as an ersatz neutral density filter,
it costs about two full stops of light. You do need fairly good
lighting to use it, in other words!
Click to expand...
Thanks for a great explanation, i just got a CPL and UV filter yesterday and my initial feeling was that the CPL does not work. I am going to try your method today to see what results i get.

Could someone explain what are advantages/disadvantages of using UV filter and a CPL filter together on a 17-55mm f/2.8? Should you only use one filter at time or does it not matter? Thanks
 
Shash703 said:
Thanks for a great explanation, i just got a CPL and UV filter
yesterday and my initial feeling was that the CPL does not work. I
am going to try your method today to see what results i get.
Click to expand...
based on what, you can look through it by eye, you should see clear results against reflections in glass or water, or darkening of the blue sky at 90 degrees to the sun.
You have to look through it from the "camera" side, otherwise it doesn't work.

See the effects in the viewfinder can be a bit more difficult if you don't know what to look for. First learn what to look for by just holding it against the eye.
Shash703 said:
Could someone explain what are advantages/disadvantages of using UV
filter and a CPL filter together on a 17-55mm f/2.8? Should you only
use one filter at time or does it not matter? Thanks
Click to expand...
Well, with more filters more chances of reflections and flare, even when multicoated. So, usually better only use one at the time.
You could also have vignetting at 17mm with the double combination.

Otherwise, there isn't really a problem using two at the time - it's less cumbersome to just add the CPL on top of the UV, if you have your UV always on your lens.
 
As the name suggests, "circular" polarisers (CP) can be rotated. Screw them on and then use the outer ring to rotate until you achieve the desired effect. I use polarising sunglasses outdoors on sunny days and I use a CP the same way.

As a previous poster said, they are most effective when pointed 90 deg from the sun (ie with the sun shining from your side). They are particularly effective at bringing up clouds. On the coast they allow the camera to see through the water surface. They intensify colours.

However, CPs on wide angle lenses? Not so good. You will get big variations in colour. Most noticeable in the sky, with parts of it dark blue and other parts washed out. You might even get some vignetting from the outer ring.

I find CPs most effective on mid range to tele lenses. I would not put a CP over a UV filter. You will seriously affect the amount of light that can pass through to the sensor. I don't use any filters at all on my L lenses. Use the cheap Canon plastic lens covers instead. Much more effective at protection. Shoot unprotected for maximum light and use CPs sparingly and only in the right circumstances.
Will B
 
Code3Collector said:
So what do you use for a wide angle lens if not a polarizer? I will
be taking a lot of mountain/lake pictures at all hours of the day,
but it will be with a wide angle lens, probably the canon 10-22. Any
other advice?
Click to expand...
You can darken the sky in Photoshop. I wouldn't buy a polarizer just because of the sky.
 
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