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Old Nov 2, 2006, 12:05 PM   #1
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What is the difference between a UV and a polarizing filter? Under what circumstances would one be prefered over the other?
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Old Nov 2, 2006, 11:16 PM   #2
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Since digital camera sensors aren't very sensitive to UV, a UV filter won't do much except protect your front lens element from poor weather and/or poor handling.

A polarizer will reduce or eliminate reflections from non-metalic surfaces, letting you see through the reflections on glass or water. By lessening reflections, the polarizer also increases color saturation and can render a sky that is more blue than it would otherwise photograph -- the degree of effect depending on the angle of the sun.

Polarizers are color-neutral, so you can use them as minus 1.5 - 2 stop neutral density filters, whereas a UV filter has little or no effect on exposure.

In my opinion, a good, multicoated polarizer is one of the "must-haves" for any photo bag.

Grant
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Old Nov 5, 2006, 8:40 PM   #3
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Sometimes a polarizer will remove reflections from glass and other times it will not. Two days ago, I was inside a shop that had large glass windows. It was late afternoon, and I pointed the camera out a window, at a right angle to the late afternoon sun.

The shop's merchandise and store fixtures reflected off the glass, making it hard to see the grass and the trees outside. When I rotated the polarizer, the reflections did not diminish.

The reflected light probably came from the wrong angle. That might explain why the reflections did not diminish. But other times the polarizer does stop reflections.

The same thing applies to darkening the sky. If you are not at the correct angle, there could be less darkening or even none. And I don't know about cloudy days.

I have only had my camera and polarizer for about 10 days now, but I am convinced -- the polarizer is necessary, and it doesn't hurt to try a photo with and without it.

Experiment and see what it does for you.

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Old Nov 16, 2006, 2:46 PM   #4
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granthagen, I've seen you respond to a lot of posts with authority and obvious expertise in camera related questions. Wanted you to know I find your responses/anwers very helpful in making my decisions.

In regard to a good circular polarizer, would it be wrong to just forget about a UV filter and leave the CP on the camera all the time?
Camera is an S3.

Changeling




granthagen wrote:
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Since digital camera sensors aren't very sensitive to UV, a UV filter won't do much except protect your front lens element from poor weather and/or poor handling.

A polarizer will reduce or eliminate reflections from non-metalic surfaces, letting you see through the reflections on glass or water. By lessening reflections, the polarizer also increases color saturation and can render a sky that is more blue than it would otherwise photograph -- the degree of effect depending on the angle of the sun.

Polarizers are color-neutral, so you can use them as minus 1.5 - 2 stop neutral density filters, whereas a UV filter has little or no effect on exposure.

In my opinion, a good, multicoated polarizer is one of the "must-haves" for any photo bag.

Grant
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Old Nov 16, 2006, 4:08 PM   #5
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No !!

Polarizing filters just like neutral density filters, block a couple of stops of light. In fact if you forget a ND filter you can use the polarizer as a stopgap..

Unlike dslrs, digicams like the S3 etc have a very limited range of stops available to them, so blocking even more light when not needed is crazy.

Uv filters do not block light, and are mostly used to protect expensive camera lens from scratches and dirt, and to keep dirt and grime from possibly entering the delicate zoom mechanism.

Buy the best, multicoated UV filter you can afford if you want to use it all the time.
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Old Nov 16, 2006, 4:42 PM   #6
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The polarization of the sky has nothing to do with reflections. At some angles to the sun the light waves interact with the atmosphere and cause some of the waves to vibrate in a particular plane or be polarized. When you rotate the polarizer so it blocks waves polarized in that direction you darken the sky.

Reflections cause the light to become polarized only at certain angles. The light is never polarized from a reflection when it is bounced directly back to you.

You don't need a circular polarizer for a S3. A linear polarizer works just as well for the same quality filter and costs less. A circular polarizer has a linear polarizer that works the same as the one on the linear polarizer. There is then another layer to the filter to rotate the light back so it isn't completely polarized. Some DSLR cameras with semi-transparent mirrors need the second stage so they can focus and meter properly. That second stage does nothing for a S3.

I agree with Sintares that it is a bad idea to leave a polarizer on the camera all the time for lens protection. Most of the time it accomplishes nothing but cut your light.

Unless you are particularly hard on a camera I don't think you need the UV either. I always had one on my film SLRs because they improved outdoor shots and didn't seem to detract from other shots. I don't personally like to have an extra piece of glass with two glass/air interfaces causing extra flare when UV is already being effectively filtered by digital cameras. Many people like to have the protection but over the years I have discovered that the lens coatings are pretty tough.

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Old Nov 16, 2006, 6:21 PM   #7
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I had just decided to fix CPL onto my camera's lens in-lieu of the UV as a permanent fixture for effect and protection as well

Advice please.
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Old Nov 16, 2006, 6:58 PM   #8
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Don't use a CPL or LPL permanently.

Use a UV filter or none at all.

A PL will lose you light, a UV will lose you no light.

Light is precious, we always need more, so deliberately crippling a cameras light gathering capability is non sensical.

Aslipe said, each layer of glass in front of a lens has the possibility to induceerrors, color casts, more pf/ca etc, and is another layer for light to bounce off and cause flare , so if you aregong to put a filter on make sure its good quality and has multicoated optics.


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Old Nov 16, 2006, 7:56 PM   #9
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Think have to agreed with you

Will switch back to my 'Hoya' UV
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Old Nov 16, 2006, 9:59 PM   #10
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Quote:
Reflections cause the light to become polarized only at certain angles.
So the polarizer can (but will not always) darken the sky. So far, I understand.

Quote:
The light is never polarized from a reflection when it is bounced directly back to you.
When I stand indoors in the daytime, close to a shop window, and look outside, there is light reflecting off the black-painted aluminum window frame. It will appear darker or lighter depending on how I rotate the polarizer.

There is a compact flourescent light pointed at my bedroom wall. Light reflects off the top of my black plastic alarm clock (and the top of the nightstand) and will appear lighter or darker as I rotate the polarizer, whether the polarizer is on or off the camera (so I know it is not the LCD playing tricks on me).

Do these examples disagree with you, or did I not understand your point? Perhaps "directly back to you" means something different than light --> surface --> my eye?

The last time there was glass between me and a museum exhibit, I had no polarizer. The camera saw my reflection in the glass (I was wearing a yellow jacket). Next time, I will have a polarizer. I want to know how to eliminate the reflection.


Quote:
The polarization of the sky has nothing to do with reflections.
Can you point me to a tutorial on polarization? Making the sky darker and stopping reflections (of natural OR artificial light) off of glass in a museum are two different things, and this might be the reason I am confused. I just want to be the best photographer I can be.

If you have any resources, let me know. I'll also look around. Thanks in advance.

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