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Old Jul 13, 2004, 3:59 AM   #1
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Just got new filter on ebay, but not sure which type it is.

How can you tell, and with a digital camera (Kyocera M410R) does it make a difference?

Thanks, Steve :?
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Old Jul 13, 2004, 9:16 AM   #2
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Hold it up to a mirror and look through the polarizer at its reflection. If it doesn't darken much it is linear. If it darkens considerably it is circular. If you take two pair of polarized sunglasses and hold them at 90 degrees from each other they will darken. The circular polarizer rotates the polarization so its reflection in the mirror acts like theglasses becausereflection are at angles to each other.

If it didn't say it is probably linear. It makes no difference at all on any digital cameras except some DSLRs. A linear polarizer just polarizes the light and you can't polarize it any better. A circular polarizer is a linear polarizer with a more complex second layer to rotate the polarization so it works with some semi-transparent mirror systems. It does absolutely nothing for you if you don't have such a camera, and you don't.
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Old Jul 13, 2004, 11:53 AM   #3
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It has been my experience that a linear polarizer performs better OPTICALLY than a circular. They are also much cheaper. The downside is that a linear polarizer can prevent SOME (not all) autofocus systems from working properly. I used a linear polarizer on a Nikon N70 for years and never had a single problem with it. My suggestion is to try the linear on your camera and if the autofocus still works ok with it then you've saved yourself some money.
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Old Jul 13, 2004, 12:12 PM   #4
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StevePn wrote:
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Just got new filter on ebay, but not sure which type it is.
How can you tell, and with a digital camera (Kyocera M410R) does it make a difference?
If it's a linear polarizer, it will usually say POL or LP on the filter ring itself...if it's a circular, it will say CP.

As for that particular camera, either will work.
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Old Jul 13, 2004, 1:46 PM   #5
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Hi

Thanks for the help. Looks like I got a bargain then....Brand New Hoya for £2.40 !!

Steve:|
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Old Jul 14, 2004, 12:41 PM   #6
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calr wrote:
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The downside is that a linear polarizer can prevent SOME (not all) autofocus systems from working properly. [...] My suggestion is to try the linear on your camera and if the autofocus still works ok with it then you've saved yourself some money.

Now I'm confused...

I thought that linear polarizers caused trouble with ANY autofocus systems. How can I know if a camera will work correctly with a linear one beforehand, so I don't have to try it and spend the money? I'm thinking of a Lumix DMC-FZ10, but if there's a general answer, like something related to the type of af system... thank you.
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Old Jul 14, 2004, 2:03 PM   #7
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José A. wrote:
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Now I'm confused...

I thought that linear polarizers caused trouble with ANY autofocus systems. How can I know if a camera will work correctly with a linear one beforehand, so I don't have to try it and spend the money? I'm thinking of a Lumix DMC-FZ10, but if there's a general answer, like something related to the type of af system... thank you.

I copied this from Cokin:

"
Polarizers come in two varieties: Linear 160 and Circular 164. Each has the same effect visually; the difference is just in the way they polarize the light passing through. If you own an auto focus or auto-exposure camera (basically any modern camera), use a 164 Circular polarizer, which won't interfere with its automatic functions. Digital cameras in general do not have reflection mirrors, and, as a result, can use both (linear or circular) polarizers." http://www.geocities.com/cokinfiltersystem/polarizer.htm

I have a FZ10 and linear polarizers work fine with it.
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Old Jul 14, 2004, 3:39 PM   #8
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José A. wrote:
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Now I'm confused...

I thought that linear polarizers caused trouble with ANY autofocus systems.
No, only cameras that use beam splitters or semi-silvered mirrors like dSLRs and some modern SLRs.
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Old Jul 24, 2004, 10:50 PM   #9
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Mikefellh wrote:
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No, only cameras that use beam splitters or semi-silvered mirrors like dSLRs and some modern SLRs.

Thank you.

How many autofocus systems are there? Where can I find more information about it?

Thank you again.
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Old Jul 25, 2004, 7:20 AM   #10
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José A. wrote:
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How many autofocus systems are there? Where can I find more information about it?
You can find information about autofocus (and lots of other things) at howstuffworks.com. Here's the start of the autofocus topic:
http://electronics.howstuffworks.com/autofocus.htm

Most digital cameras use a contrast detection focusing, which is the same as "passive autofocus" described in the above site.

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