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View Poll Results: Will Linear PL filter work with K100D without problems?
YES 428.57%
NO 1071.43%
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12-13-2007, 07:27 AM   #1
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CPL or LPL ?

Hi guys,
I have ran across several thread discussing polarising filters and other matters coming along. I have read several posts saying that cameras like *ist DS2, Samsung DSLRs and so on are perfectly fine with LPL, despite camera's (K100D's) manual recommends to use strictly CPL. Now as far as I know, all Pentax DSLR from *ist DL/S 2 onwards and all Samsungs are using Safox VIII AF system and roughly the same (if not indentical) AE system. So my question is:
Is it reasonable to spend all that extra cash on CPLs when there are several people working OK with LPLs with cameras using the same AF/AE as mine?!?
What do you think? or what's your experience?
TIA
Peter

12-13-2007, 09:19 AM   #2
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I've only used circular ones, but that is because I have heard they are much better than linear. I don't even really know what a linear one does. I am very happy with my circular filter, it is one of my favorite toys.
12-13-2007, 10:44 AM   #3
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yes, Circular Polarizers are expensive. Much more expensive than the linears. I don't know what situations will result in erroneous exposure and/or focus when you use the linear, and I don't want to find out. I use circulars. The problem is interference with the half silvered center of the mirror that splits light between the viewfinder prism and the focus and exposure sensors in the mirror box.
12-13-2007, 10:59 AM   #4
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QuoteOriginally posted by travis_cooper Quote
I've only used circular ones, but that is because I have heard they are much better than linear. I don't even really know what a linear one does. I am very happy with my circular filter, it is one of my favorite toys.
They aren't better per se. They just have an additional layer which "re-scrambles" the polarized light, which keeps the beam-splitter which reflects light up to the AF and metering system from (potentially) causing a blackout due to overlapping polarizations. (Take two linear polarizing filters and put them on top of each other, then turn one and watch what happens.)

I've heard but not verified (or seen demonstrated) that this additional layer causes a less-dramatic polarization effect, so in that sense linear may be better after all.

It also makes sense that at many angles there would be no problem with a linear polarizer but that at others you may get erroneous metering. Certainly people have reported here that they've used 'em with no problem.

12-13-2007, 04:13 PM   #5
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where is the "maybe" option? All i know is my linear poariser works with my istDS (and worked with my Nikon F65). Don't know if that means it would work with a K100D.
12-14-2007, 08:25 PM   #6
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I agree with Arpe's "maybe" option. A linear polarizer would probably work just fine perhaps 99% of the time, but always with a tiny chance it will screw things up in difficult or unusual focusing or metering situations. I don't know about you, but I have enough things on my mind without adding something like this while reliable alternatives (circular polarizers) are so readily available.

By the way, adding to mattdm's comments, a total blackout is unlikely, but even various levels of reduced lighting (a so-called brownout) approaching either side of a total blackout might impact metering or make auto-focusing more difficult.

stewart



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Last edited by stewart_photo; 12-14-2007 at 10:28 PM.
12-14-2007, 08:56 PM   #7
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I have the 16-50 f2.8 lens for my K10D. The filter size is 77mm. CPL's at B&H run from $68 to $309. Wowzers! How to choose.

Interesting article at The Luminous Landscape: Polarizers
12-14-2007, 09:10 PM   #8
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I did a fair amount of reading to try and clarify the differences and if an LP would be fine. They can work ok but not always. A CPL has a second layer to reconsitute the light rays as they pass through the polarized lens. Think of a polarized lens as a set of blinds. they bend the light. The second layer corrects this bending of the light. So I bid on a large Ebay auction and it included a 49mm LP in the group. So I tested it for a few hours and over a few days in various situations.

When the polarization was light, the lens had no issues focusing. In other situations where I put more adjustment in, the lens had trouble focusing and would often front focus and have difficulty locking focus. The lens worked better in spot focus but got confused more often in multi point focus mode.

So the result is they do work but can have trouble in some situations.

12-14-2007, 10:27 PM   #9
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QuoteOriginally posted by wtlwdwgn Quote
I have the 16-50 f2.8 lens for my K10D. The filter size is 77mm. CPL's at B&H run from $68 to $309. Wowzers! How to choose.

That's a real good question. Beyond mount thickness, multi-coating seems to be the primary difference between the expensive and less expensive filters. Given polarizers are used most often at angles to the sun (not with the sun falling directly onto the filter causing flare), has anyone actually found a situation where multi-coated polarizers truly work better then single-coated polarizers?

I believe my less expensive Tiffen polarizer is not multi-coated, without any problems so far. But that alone doesn't mean there will never be problems.

stewart
12-14-2007, 11:23 PM   #10
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I was of the thinking that two (linear) polarizers turned at 90degrees would give a completely black (no light transmission) but I just tried it and it's dark, but not completely black. I've read you can use the effect to simulate a (variable) ND filter but have never tried it myself.

Cheers, Nige
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