Linear Polarizing Filter

slackercruster · 03-24-2012, 06:35 PM

How do they differ from standard polarizers?

Why are they so cheap?

newarts · 03-24-2012, 06:46 PM

A Circular Polarizer is a Linear Polarizer with a second element called a "quarter-wave plate" added. The extra element is needed for some cameras. (not K-x, for example). The extra element basically un-polarizes light.

If a linear polarizer is sufficient for your camera, it is most likely preferable. Less chance of defect, less light tinting possibility.

What ever you get should be multicoated. See lenstip.com for a review of polarizers.

slackercruster · 03-24-2012, 06:59 PM

Thanks!

stevebrot · 03-24-2012, 08:15 PM

Originally posted by newarts

The extra element is needed for some cameras. (not K-x, for example).

Truly!? It was my understanding that linear polarizers cause problems with the AF system and that the problem is characteristic of all AF SLRs that use the main mirror as a beam splitter.

So, the short answer is that if you restrict your use of a linear polarizer to manual focus, there should be no problem.

Steve

Philoslothical · 03-24-2012, 09:21 PM

Originally posted by newarts

A Circular Polarizer is a Linear Polarizer with a second element called a "quarter-wave plate" added. The extra element is needed for some cameras. (not K-x, for example). The extra element basically un-polarizes light.

If a linear polarizer is sufficient for your camera, it is most likely preferable. Less chance of defect, less light tinting possibility.

This is also the first I've heard of using linear polarizers on PDAF DSLRs. I understand that we should be immune to the metering issues caused by linear polarizers on some systems, but we're still susceptible to loss of light from cross polarizing. AF may still work if there is sufficient light, but it may interfere to some degree.

**dms** · 03-24-2012, 10:59 PM

I use linear PL w/ K20D, and I have no metering problems. In another posting I said same and another poster said metering matte card there was a difference depending on the PL filter position. That is not what I get with regular indoor lights! Maybe he was using outdoor lighting--which has a PL'd component.

Philoslothical · 03-24-2012, 11:12 PM

As I said, you won't have metering issues with a Pentax DSLR and a linear polarizer. Pentax doesn't use any kind of beam splitter for metering, so, no cross polarizing can happen in that context.

Anvh · 03-25-2012, 04:47 AM

Originally posted by Philoslothical

This is also the first I've heard of using linear polarizers on PDAF DSLRs. I understand that we should be immune to the metering issues caused by linear polarizers on some systems, but we're still susceptible to loss of light from cross polarizing. AF may still work if there is sufficient light, but it may interfere to some degree.

Tested the metering linear vs circular and the linear give an error of 1 stop between minimum and maximum and this as indeed when metering a matt surface.
The circular holds his metering in those situation.
This was with the K10D and K20D if i remember correctly.

http://www.pentaxuser.co.uk/forum/topic/why-are-polorising-filters-so-expens...p-0#comm183304

**Lowell Goudge** · 03-26-2012, 04:55 AM

Not quite sure about the complete technical accuracy of new arts response as it is perhaps over simplified, but to make a long story short, it is thenAF and not the metering that is impacted by a linear polarizer, at least this is what people who sell them want you to believe. I have never had an issue with linear polarizes on my Pentax lenses/cameras

**luftfluss** · 03-26-2012, 11:51 AM

Originally posted by Lowell Goudge

I have never had an issue with linear polarizes on my Pentax lenses/cameras

Ditto.

demp10 · 03-26-2012, 12:08 PM

The camera's mirrors used to split the light for AF and exposure metering will act as polarizers themselves. If the incoming light is already polarized as in the case of a linear polarizer, there is a chance, depending on the angle of polarizations, to cancel a significant amount of light and cause the AF system to malfunction due to "low" light. Same for the exposure meter.

A circular polarizer, twist the polarized light coming out of its front linear polarizer so there is light in all angles reaching the mirrors.

If you use manual focus and ignore focus confirmation, you will not notice any difference between the two types other than some exposure variation under specific angles.

Philoslothical · 03-26-2012, 02:01 PM

Originally posted by demp10

Same for the exposure meter.

Except that, AFAIK, no Pentax DSLR uses a beam splitter for its exposure metering, so an LPL is only going to affect AF. You do lose some light with any polarizer, which affects exposure, but that's the normal, intended effect. Cross polarizing of light hitting the meter isn't an issue.

demp10 · 03-26-2012, 03:35 PM

Originally posted by Philoslothical

Except that, AFAIK, no Pentax DSLR uses a beam splitter for its exposure metering, so an LPL is only going to affect AF. You do lose some light with any polarizer, which affects exposure, but that's the normal, intended effect. Cross polarizing of light hitting the meter isn't an issue.

My understanding is that the exposure system is behind the focusing screen inside the pentaprism housing and the autofocus system is at the bottom below the mirror.

The main mirror has a semi-transparent window to let light hit a secondary mirror below for the AF system.

Part of the reflected light that reaches the focusing screen is provided by the semi-transparent window. If that window, and the secondary mirror and AF system below, are sensitive to the polarization angle, they will reduce the reflected light and the exposure will be off.

03-24-2012, 06:35 PM	#1
slackercruster Veteran Member Join Date: Jan 2012 Location: NE, USA Posts: 1,302	Linear Polarizing Filter How do they differ from standard polarizers? Why are they so cheap?

03-25-2012, 04:47 AM	#8
Anvh Veteran Member Join Date: Sep 2011 Posts: 4,616	Originally posted by Philoslothical This is also the first I've heard of using linear polarizers on PDAF DSLRs. I understand that we should be immune to the metering issues caused by linear polarizers on some systems, but we're still susceptible to loss of light from cross polarizing. AF may still work if there is sufficient light, but it may interfere to some degree. Tested the metering linear vs circular and the linear give an error of 1 stop between minimum and maximum and this as indeed when metering a matt surface. The circular holds his metering in those situation. This was with the K10D and K20D if i remember correctly. http://www.pentaxuser.co.uk/forum/topic/why-are-polorising-filters-so-expens...p-0#comm183304 Last edited by Anvh; 03-25-2012 at 04:54 AM.

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03-24-2012, 06:46 PM	#2
newarts Inactive Account Join Date: Dec 2008 Location: Ames, Iowa, USA Photos: Albums Posts: 2,965	A Circular Polarizer is a Linear Polarizer with a second element called a "quarter-wave plate" added. The extra element is needed for some cameras. (not K-x, for example). The extra element basically un-polarizes light. If a linear polarizer is sufficient for your camera, it is most likely preferable. Less chance of defect, less light tinting possibility. What ever you get should be multicoated. See lenstip.com for a review of polarizers.

03-24-2012, 06:59 PM	#3
slackercruster Veteran Member Join Date: Jan 2012 Location: NE, USA Posts: 1,302 Original Poster	Thanks!

03-24-2012, 08:15 PM	#4
stevebrot Otis Memorial Pentaxian Join Date: Mar 2007 Location: Vancouver (USA) Photos: Gallery \| Albums Posts: 42,007	Originally posted by newarts The extra element is needed for some cameras. (not K-x, for example). Truly!? It was my understanding that linear polarizers cause problems with the AF system and that the problem is characteristic of all AF SLRs that use the main mirror as a beam splitter. So, the short answer is that if you restrict your use of a linear polarizer to manual focus, there should be no problem. Steve

03-24-2012, 09:21 PM	#5
Philoslothical Veteran Member Join Date: May 2011 Posts: 1,889	Originally posted by newarts A Circular Polarizer is a Linear Polarizer with a second element called a "quarter-wave plate" added. The extra element is needed for some cameras. (not K-x, for example). The extra element basically un-polarizes light. If a linear polarizer is sufficient for your camera, it is most likely preferable. Less chance of defect, less light tinting possibility. This is also the first I've heard of using linear polarizers on PDAF DSLRs. I understand that we should be immune to the metering issues caused by linear polarizers on some systems, but we're still susceptible to loss of light from cross polarizing. AF may still work if there is sufficient light, but it may interfere to some degree.

03-24-2012, 10:59 PM	#6
dms Site Supporter Join Date: Aug 2011 Location: New York, NY Photos: Gallery Posts: 2,192	I use linear PL w/ K20D, and I have no metering problems. In another posting I said same and another poster said metering matte card there was a difference depending on the PL filter position. That is not what I get with regular indoor lights! Maybe he was using outdoor lighting--which has a PL'd component.

03-24-2012, 11:12 PM	#7
Philoslothical Veteran Member Join Date: May 2011 Posts: 1,889	As I said, you won't have metering issues with a Pentax DSLR and a linear polarizer. Pentax doesn't use any kind of beam splitter for metering, so, no cross polarizing can happen in that context.

03-26-2012, 04:55 AM	#9
Lowell Goudge Site Supporter Join Date: Jan 2007 Location: Toronto Photos: Gallery \| Albums Posts: 17,888	Not quite sure about the complete technical accuracy of new arts response as it is perhaps over simplified, but to make a long story short, it is thenAF and not the metering that is impacted by a linear polarizer, at least this is what people who sell them want you to believe. I have never had an issue with linear polarizes on my Pentax lenses/cameras

03-26-2012, 11:51 AM	#10
luftfluss Site Supporter Join Date: Jun 2011 Location: NJ Photos: Gallery \| Albums Posts: 11,619	Originally posted by Lowell Goudge I have never had an issue with linear polarizes on my Pentax lenses/cameras Ditto.

03-26-2012, 12:08 PM	#11
demp10 Veteran Member Join Date: Jun 2011 Location: Atlanta Photos: Albums Posts: 602	The camera's mirrors used to split the light for AF and exposure metering will act as polarizers themselves. If the incoming light is already polarized as in the case of a linear polarizer, there is a chance, depending on the angle of polarizations, to cancel a significant amount of light and cause the AF system to malfunction due to "low" light. Same for the exposure meter. A circular polarizer, twist the polarized light coming out of its front linear polarizer so there is light in all angles reaching the mirrors. If you use manual focus and ignore focus confirmation, you will not notice any difference between the two types other than some exposure variation under specific angles.

03-26-2012, 02:01 PM	#12
Philoslothical Veteran Member Join Date: May 2011 Posts: 1,889	Originally posted by demp10 Same for the exposure meter. Except that, AFAIK, no Pentax DSLR uses a beam splitter for its exposure metering, so an LPL is only going to affect AF. You do lose some light with any polarizer, which affects exposure, but that's the normal, intended effect. Cross polarizing of light hitting the meter isn't an issue.

03-26-2012, 03:35 PM	#13
demp10 Veteran Member Join Date: Jun 2011 Location: Atlanta Photos: Albums Posts: 602	Originally posted by Philoslothical Except that, AFAIK, no Pentax DSLR uses a beam splitter for its exposure metering, so an LPL is only going to affect AF. You do lose some light with any polarizer, which affects exposure, but that's the normal, intended effect. Cross polarizing of light hitting the meter isn't an issue. My understanding is that the exposure system is behind the focusing screen inside the pentaprism housing and the autofocus system is at the bottom below the mirror. The main mirror has a semi-transparent window to let light hit a secondary mirror below for the AF system. Part of the reflected light that reaches the focusing screen is provided by the semi-transparent window. If that window, and the secondary mirror and AF system below, are sensitive to the polarization angle, they will reduce the reflected light and the exposure will be off.