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Old Sep 22, 2003, 6:04 AM   #1
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Default linear or circular? ...polarizing filter (s5000,s602,s7000)

So which one does it work best? Can anyone shed some light into it please?

Thanks.
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Old Sep 22, 2003, 9:57 PM   #2
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Default Re: linear or circular? ...polarizing filter (s5000,s602,s70

Quote:
Originally Posted by veedee
So which one does it work best? Can anyone shed some light into it please?
There is no difference between these two if you use them on a consumer type, non-SLR or non-DSLR camera. Buying a multi-coated one is more important than choosing from linear and circular.

CK
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Old Sep 23, 2003, 10:17 PM   #3
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Default Re: linear or circular? ...polarizing filter (s5000,s602,s70

Quote:
There is no difference between these two if you use them on a consumer type, non-SLR or non-DSLR camera. Buying a multi-coated one is more important than choosing from linear and circular.
I'm sorry but that's not quite true. :?

There is a big difference between linear and circular polarizers. Most newer camera auto exposure circuits will not work correctly with linear polarizers. These circuits need to have the light coming through the polarizer "rescrambled" (rough explanation) before it strikes the internal photocell of the camera. If not, your exposures will be off. Circular polarizers are essentially linear polarizers with a secondary ("birefringent") element attached to the back side of the filter. This is why circular polarizers are more expensive than linear polarizers.

~Laserjock~
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Old Sep 24, 2003, 9:41 AM   #4
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For the cameras that you mentioned you will need a circular polarized filter for the reasons that Laser Jock mentioned.
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Old Sep 25, 2003, 2:37 AM   #5
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Default Re: linear or circular? ...polarizing filter (s5000,s602,s70

Quote:
Originally Posted by Laserjock
I'm sorry but that's not quite true. :?

There is a big difference between linear and circular polarizers. Most newer camera auto exposure circuits will not work correctly with linear polarizers. These circuits need to have the light coming through the polarizer "rescrambled" (rough explanation) before it strikes the internal photocell of the camera. If not, your exposures will be off. Circular polarizers are essentially linear polarizers with a secondary ("birefringent") element attached to the back side of the filter. This is why circular polarizers are more expensive than linear polarizers.
You have the general "theory" part right. However, you perhaps are not aware why circular polarizers must be used in a SLR and D-SLR while a linear polarizer can be used with consumer type cameras. It is not because "[light meter] circuits need to have the light coming through the polarizer "rescrambled" (rough explanation) before it strikes the internal photocell of the camera." Here is the reason.

Some cameras use a beamsplitter that diverts the incoming light. A portion of the incoming light passes through the beamsplitter to reach the AF module and/or the light meter, while the other portion is diverted to the viewfinder. This split should be constant so that the AF module and meter can work properly. Otherwise, the AF module may fail if the incoming light is not strong enough (for most SLR and DSLR, F5.6 is the limit), and/or the light meter will not deliver a correct reading.

If a linear polarizer is mounted in front a lens, as it is being rotated, because the incoming light is polarized in one direction (a simplified version to avoid math and physics), the beamsplitter may divert different portions to the viewfinder and the AF module/meter, and the proportion of the incoming light that can reach the AF module and meter system is not constant. Consequently, metering cannot deliver correct measure, casuing inciorrect exposure. On the other hand, a circular polarizer redistributes the polarized light (again, a simplified version) so that the beamsplitter can diverte a constant portion to viewfinder and AF module/meter. In this way, the meter will work properly.

This beamsplitting technique is usually used in SLR and D-SLR cameras with a flipping mirror. As for P&S film and consumer level digital cameras, there is no beamsplitter to split the incoming light, the above described problem will not happen. Of course, one can use linear polarizers. In fact, almost all consumer type digital cameras either use EVF's or range-finder type viewfinders to save cost and make size smaller. We can safely say that, even with the newest one, there is no beamsplitter inside a consumer type non-SLR and non-DSLR digital camera.

CK
http://www.cs.mtu.edu/~shene/DigiCam
Nikon Coolpix 950/990/995/2500/4500 User Guide
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Old Sep 25, 2003, 7:48 AM   #6
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shene, thanks a lot for your answer. also, congratulations for your really nice webpage. I got some suggestions for it, like put everything that's not camera-dependable (filter explanations, etc) on the left side near the cameras you tested also. a lot easier to access that info this way, since not all people are interrested in Nikon.

about the polarizer filter... I ordered a cokin 55mm one, should get here friday or saturday. I choosed linear after reading several posts on different forums on the Internet where S602 users said that linear works better than circular with their cameras.

Cheers,
veedee.
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Old Sep 26, 2003, 1:46 AM   #7
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Shene, I am not here to argue semantics. I was just trying to claify that your statement that coatings were more important than the class of polarizer that you use was incorrect. I see alot of misinformation being doled out here in these forums and I stand behind my explanation. Also, it is incorrect to state that linear polarizers affect autofocus circuits, they only affect light metering circuits. Most modern AF circuits use contrast to focus with.

Here is a "technical" explanation for CPs:

Circular polarizers are 2-layer affairs—a linear polarizer (LP) backed with a special birefringent optical layer known as a quarter-wave plate (QWP). The QWP is bonded to the LP with its fast optical axis oriented 45° to the LP's passing axis. In this configuration, the QWP transforms the linearly polarized light emerging from the outer LP layer into circularly polarized light, which to the polarization-sensitive metering and auto-focus components found in many modern SLR cameras is indistinguishable from unpolarized light.

Try this experiment if you think I am still incorrect. Hold a circular polarizer up in front of a linear polarizer and rotate one with respect to the other. Note what happens as your do this, you will not be able to extinguish the light coming through the two polarizers (as with two LPs), this is due to the properties of the birefringent material in the CP. Now move the linear polarizer in front of the CP and rotate one with respect to the other, the light coming through both polarizers will extinguish (this is equivalent to holding two LPs up to each other). You are correct, the light exiting a CP is not "rescrambled", It was a loose explanation of how the QWP layer introduces a secondary electromagnetic plane wave phased 90deg out from the original plane wave.

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Old Sep 26, 2003, 2:16 AM   #8
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thanks for all your explanations guys. I already read the "technical" parts. I wanted to know from someone's experience how does each perform with a S5000 (s602 would do fine) in a real-world test.
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Old Sep 26, 2003, 2:54 AM   #9
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Quote:
Originally Posted by Laserjock
I was just trying to claify that your statement that coatings were more important than the class of polarizer that you use was incorrect.
For consumer type non-SLR digital cameras, which is the assumption that I made very clear in my post, costing is indeed more important than the distinction between linear and circular, because one does not have to worry about whether the polarizer being used is linear or circular. So, I don't see the incorrectness in my statement. Forgive me, if I am wrong; however, my knowledge in optical engineering provides me the necessary backup.

Quote:
Originally Posted by Laserjock
Also, it is incorrect to state that linear polarizers affect autofocus circuits, they only affect light metering circuits. Most modern AF circuits use contrast to focus with.
Yes, a linear polarizer does affect AF focus in general. This is because the beamsplitter cannot maintain a constant split of the incoming light to the AF module. When a linear polarizer is rotated to some position that causes the light split to the meter and/or AF module becoming so low that is less than the needed intensity, AF module, especially those contrast-based AF systems, will fail to lock on the subject. Most contrast-based AF systems need the incoming light to be around F5.6. Since lower intensity implies lower contrast, if the light diverted to the AF module is less than the minimum level, contrast will be so low that the AF module cannot operate properly.

If you are interested some easy reading, here is a good undergraduate textbook: http://www.amazon.com/exec/obidos/tg...glance&s=books

CK
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Old Sep 26, 2003, 3:34 AM   #10
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Quote:
Originally Posted by veedee
I wanted to know from someone's experience how does each perform with a S5000 (s602 would do fine) in a real-world test.
I have a linear polarizer and a circular polarizer for Cokin's A- and P- systems, and use them regularity with my Coolpix cameras (i.e., 950, 990, 995, 4500, 5000 and 5700, and sometimes 2500 and SQ). My finding is that no difference in effect between linear and circular polarizers. Or, a more accurate (and scientific) way to say it is that the difference is very little that may be unnoticeable. Just don't worry about this blown out of proportion problem. (Or, think it this way. If linear polarizers are so problematic, all manufacturers could have closed their production lines long long time ago. ) Go out and shoot something with your new polarizer on, and you will have the same conlusion.

CK
http://www.cs.mtu.edu/~shene/DigiCam
Nikon Coolpix 950/990/995/2500/4500 User Guide.
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