[BruceBanner]

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I just wondered, some stuff I read suggests Linear polarizers are still perfectly fine, in fact may even be better than Circular in certain conditions. I realise that using a Linear can throw exposure off, and then also if using AF make that aspect wonky... but if your sole intention of using a polarizer is landscape, tripods etc, then does it matter about circular?

Like... when I do landscape anyway, I'm tripod for long exposures of water or clouds, or I'm using Pixel Shift. All of this means I chimp after the shot to check exposures, focus etc, so if Linear throws exposure or focus off... after I chimp once I can just accommodate easily enough for it? And all my landscape tends to be Manual Focus, either to infinity or Hyper-focal stuff etc, I just use Live View for it all anyway...

Not only are Linear cheaper (significantly) but I read some say they are better (than Circular)? If using a Linear for landscape, and a fairly wide focal length, does Linear produce a more even blue sky across the frame more than circular?

I'm just trying to think of all the occasions I'd need to rely on AF with a polarizer attached and be concerned with correct exposure. I'm currently shooting exclusively manual focus and actually enjoying the results a lot, exposure wise I tend to underexpose anyway and shoot RAW to deal with shadow retrievals etc.

Cheers,

Bruce

[Alex645]

Bruce, I love how you think outside the box. From my experience, I would say yes....if youʻre not using AF and are not using the cameraʻs internal light meter and shooting with manual exposures, a linear polarizer will work just fine with digital sensors.

In terms of a more even blue sky with a wide angle lens? I have not read of any evidence or explanation why a linear polarizer would not have the same issues with a wide angle lens as a circular polarizer. Circular polarizers are in fact linear polarizers with an added layer quarter wave plate which would have no benefit in increasing the angle of the polarization effectiveness. So IMO, no.

[BruceBanner]

Bruce, I love how you think outside the box. From my experience, I would say yes....if youʻre not using AF and are not using the cameraʻs internal light meter and shooting with manual exposures, a linear polarizer will work just fine with digital sensors.

In terms of a more even blue sky with a wide angle lens? I have not read of any evidence or explanation why a linear polarizer would not have the same issues with a wide angle lens as a circular polarizer. Circular polarizers are in fact linear polarizers with an added layer quarter wave plate which would have no benefit in increasing the angle of the polarization effectiveness. So IMO, no.

Thanks, my mentality is ingrained from living in Scotland for over 20yrs... wherever possible to be tight fisted... we'll manage it

[Bob 256]

Same here. A linear will produce exactly the same polarizing effects as a CP - just the camera side-effects to deal with due to the polarized light. A CP starts with a linear polarizer out front and once it does its job, a second layer (a phase retarder) converts the linear polarized light to CP which has fewer issues with angled mirrored surfaces (hence the exposure meter), and viewfinders which contain LCD panels (which themselves use linear polarized elements). Once the sky is darkened with that linear polarizer, converting to CP doesn't change that or alter the image in any way. It just makes the linear polarized light circular so it won't affect things downstream from the lens.

Whether one is better than another - it just depends on the quality of the linear polarizer layer (first one in a CP). It that layer is an efficient polarizer, the whole thing works well. If it is a cheap polarizer that doesn't work well, linear or CP, the whole thing works poorly. Once exception is that the retarder layer in a CP can introduce a slight color cast so potentially, a linear polarizer could perform better.

Your thinking should work fine.

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Last edited by Bob 256; 04-17-2018 at 08:11 AM.

[link81]

I thought i remembered reading something somewhere that Pentax camera's didn't care if it was linear or circular. Something about the AF module or something. (sorry, don't have the reference)

[Ontarian50]

Circular polarizers are needed when there's a beam splitter in the light path. Beam splitters have a polarizing effect.

Since an AF SLR mirror works as a beam splitter, and diverts some light down to the focusing module in the bottom of the mirror box, a linear polarizer ends up being at cross purposes sometimes, depending on how its oriented, and next to no light gets through to the AF module - so AF goes on the fritz. Since a circular polarizer re-randomizes the polarization of the light (ie: makes it circular in orientation again) the AF system works again.

But circular polarizers have been around longer than AF systems. They were needed on some cameras that used beam splitters in the exposure system - where the meter cell was hidden behind a semi-transparent mirror (Leica R3, for instance), or like the Canon F-1 and FTb where the focus screen had a beam splitter that directed light towards the meter cell.

Most cameras, and I think including all Pentax SLRs and DSLRs, had the meter cells beside the eyepiece and looking straight at the focus screen - and didn't have any beam splitting going on, and didn't need a costly circular polarizer (they were rarer and more pricey back then).

So, while a linear polarizer will muck up your AF system, if you've got AF turned off you've got no problem. But it should have no effect on your exposures, since Pentaxes don't employ beam splitters in the meter path.

[Alex645]

But it should have no effect on your exposures, since Pentaxes don't employ beam splitters in the meter path.

This is news to me. Can you post any links that supports that all Pentaxes using a linear polarizer will not have an effect on metering? Ideally not from a forum but from Pentax, a linear polarizer maker, or an article?

[Bob 256]

..................Most cameras, and I think including all Pentax SLRs and DSLRs, had the meter cells beside the eyepiece and looking straight at the focus screen - and didn't have any beam splitting going on, and didn't need a costly circular polarizer (they were rarer and more pricey back then).

So, while a linear polarizer will muck up your AF system, if you've got AF turned off you've got no problem. But it should have no effect on your exposures, since Pentaxes don't employ beam splitters in the meter path.

Your statement got me to thinking so I popped a linear polarizer on my K-1 and focused (actually de-focused) on a blank wall with a diffuse surface.

Rotating the polarizer produced no more than half an f-stop of variation (probably a bit less than that). Metering indicated that the shutter speed at a fixed f-stop varied from 1/125 to 1/100 and the EV indicator showed a variation below half a stop.

From this, it appears that the K-1 at least, is pretty immune to any changes in polarization of the incoming light so little would be gained with a CP. I can't say this applies to other Pentax cameras, but it answers the question for me regarding the K-1.

I do know that my old film Pentax had a significant variation and that's when I went to CP filters (also couldn't "chimp" film very well to compensate). I might go back to those old filters but for the fact that the CP filters are much better quality with anti-reflection coatings (glad I never throw anything away).

[Alex645]

Your statement got me to thinking so I popped a linear polarizer on my K-1 and focused (actually de-focused) on a blank wall with a diffuse surface.

Rotating the polarizer produced no more than half an f-stop of variation (probably a bit less than that). Metering indicated that the shutter speed at a fixed f-stop varied from 1/125 to 1/100 and the EV indicator showed a variation below half a stop.

Bob,
Interesting. Wouldnʻt you get different results if the light reflecting thru the filter be at different angles? In other words a real situation where there the polarizer is reducing a lot of glare from 90 degree sources?

[maw]

Let's clarify the real reasons that have brought this problem between PL and CPL filters to the fore? Does anyone know?

Let's take a step back, someone will have wondered why the fantastic Pentax LX, reflex film era has to do with linear polarizing filters and circular?

[Bob 256]

Bob,
Interesting. Wouldnʻt you get different results if the light reflecting thru the filter be at different angles? In other words a real situation where there the polarizer is reducing a lot of glare from 90 degree sources?

Yes. That's true for a scene in which some of the light is polarized by angled surfaces (and the sky), but the change in exposure seen there is just the camera readjusting to get what it thinks is a correct exposure.

For example, if you place a 0.3 neutral density filter over the lens, you would see the camera bump the exposure by 1 f-stop to compensate.

Same with the polarizer (actually two bumps since the polarizer is a bit of an ND filter as well as a polarizer). In some cases, one might need to crank in some exposure compensation to get darker skies since the camera could fight that polarizer effect by increasing the exposure and bringing the skies back toward where they were before the polarizer is adjusted for sky darkening.

To test the exposure system's sensitivity to changing the rotation of the polarizer, I shot a diffuse wall which reflects very little polarized light. The light getting to the camera metering system is polarized by the filter only and rotates as the filter is rotated so if it has any change in sensitivity as the "sense" of the polarized light changes, it would show up as a differing exposure as the filter is turned. Assuming that produces no exposure change, the changes seen in a real life shot are due to actual darkening of parts of the scene due to the filter not passing as much light for those portions and the metering system would respond to that.

Hope that's not too long winded.

[pentaxfall]

I'm just trying to think of all the occasions I'd need to rely on AF with a polarizer attached and be concerned with correct exposure..

I think CPL is mostly used for shooting static subjects(except water), and so AF can be avoided.


There was a lively thread about LPL and CPL comparison. I am not able to find the actual thread, but these two links are from that thread. I had bookmarked these two link as I found them interesting
autofocus - Why do AF systems have polarizing elements? - Photography Stack Exchange

This is very informative
All about Polarizers - Linear and Circular

[BruceBanner]

Thing is, all the stuff I find on the net for reviews on polariser filters etc, they all seem to be CPL, do we know of any good linear ones?

Polarizing filters test 2015 - Results and summary - LensTip.com

It's not the first time that site has praised Hoya for it's performance vs price (value), I think I ended up with choosing Hoya UV filters (for protection) based on that sites findings also. I keep seeing things being close between Hoya and B+W, so maybe just grab a Hoya Linear filter?

Hoya 52mm Linear Polarizer Filter B-52PL-GB B&H Photo Video ?

Two more points;

1) You can't vary the 'strength' with linear, like rotate it like you can a CPL and decide how much polarising effect to go for, with linear it's all or nothing?

2) Can you use linear (or even CPL for that matter) with ND filters if you feel you want to block out even more light. Perhaps for example a 1-2min very bright day with clouds scene to get the clouds really moving etc.

[Alex645]

Thing is, all the stuff I find on the net for reviews on polariser filters etc, they all seem to be CPL, do we know of any good linear ones?

Two more points;

1) You can't vary the 'strength' with linear, like rotate it like you can a CPL and decide how much polarising effect to go for, with linear it's all or nothing?

2) Can you use linear (or even CPL for that matter) with ND filters if you feel you want to block out even more light. Perhaps for example a 1-2min very bright day with clouds scene to get the clouds really moving etc.

I think it's hard to find any new LPL of quality because even if they only affect AF, they render all modern cameras only partially compatible. Try to find a new LPL with multicoating or Kaesemann? Nearly impossible.

You can vary the strength with LPL much like CPL, although the shift may have less variation. And yes, you can use a linear with an ND filter to reduce light.

[BruceBanner]

I think it's hard to find any new LPL of quality because even if they only affect AF, they render all modern cameras only partially compatible. Try to find a new LPL with multicoating or Kaesemann? Nearly impossible.

You can vary the strength with LPL much like CPL, although the shift may have less variation. And yes, you can use a linear with an ND filter to reduce light.

I actually just had a hunt around, and this side of the globe Linear still seem pricey, we don't get those 'B&H prices' over here.

For example I found the Hoya CPL rated number one by that aforementioned lens tip site for $73AUD, whereas linear variants are like $35ish, might as well just get the CPL and be done with it.

Hoya 52mm Fusion Antistatic CIR-PL Filter Circular Polarizer CPL Slim Genuine 24066061188 | eBay