[Mike Cash]

On SLR cameras use a circular polarizer.

I use a linear polarizer on mine.

What did I miss by not paying four times as much money for a circular polarizer?

[Ben_Edict]

I know I should do a search, but thought I would hit some of you experts up with a beginner question.

Polarizers...

Linear, Circular...

What am I supposed to see? I look for reflections on screen, or the water in the pond behind our home, and I eliminate them by turning the filter. Am I doing this correctly? I've seen the pictures of 'with' and 'without' but don't see the results.

When I turn the filter, I get two spots on the 360 degree circle that brighten the viewfinder, and two that darken as well as eliminate shadows. Is the latter the correct position.

When would you use a linear vs a circular?

I want to expand a bit on polarizers. Technicallities first:

A polarizer will reduce reflections on non-metallic surfaces, i.e. on all surfaces that are not conductive, by removing those parts of the light which are polarized at an 90 deg angle to the polarizer's own pass-through-angle. You can imagine a polarizer to be a simple fence with parallel rods. Only the light passes through the fence which oscillates parallel to the fence rods, whereas light perpendicualr to the rods will be stopped by the fence.

1. polarizers only work noticeably, when there is polarized light! That means, that on dull, foggy, misty etc, days, they won't show much or any effect at all.

2. on sunny days with clear skies, a large proportion of the sun light is polarized. On these days a polarizer works best. It removes a large proportion of the polarized light and thus the blue sky gets darker. On esuch a day foilage, water surfaces etc. will also reflect a large amount of that naturally polarized sun light and that can be removed with the polarizing filter.

You will then see an increase in saturation of greens etc. And you may be able, to look through the water surfgace and see the sand and pebbles etc. on the ground, which otherwise would be hidden by the reflecting water surface.
The same effect works with glass windows, if you place the polarizing filter at an agle with the glass and the incoming light.

3. polarizers have no officially "correct" position (they are no politicians…) You need not use them at full throttle. Sometimes just a slight application looks much better, because removing too much reflectios on foilage and achieving a really dar blue sky simply looks unnatural.

With the rotating filter mount, it is easy to find a pleasing position.

4. Circular versus Linear Polarizing Filters: As Mike Cash and Just1MoreDave have already written, there is in most cases no real need for a CPL.

A linear polarizer will only affect camera exposure meters, when they are located behind a secondary mirror (split beam mirrors), which was mainly the case with some film cameras like the Pentax LX. In our Pentax DSLRs the meter cell is located in the prism housing (a very traditional design) and is thus not affected by the polarization, that such a split-beam mirror introduces. A polarizing split-beam mirror + a linear polarizing filter would irritate the exposure system massively.

What can be affected is the AF sensor. But not by giving fals reading (and off focus), but only, because a linear polarizer would let much less light through to the AF sensor, than a CPL. That means, the AF sensor may stop working with a linear polarizer, under not so bright light.

BUT as a polarizer mainly makes sense (see above) for use under bright sun light (we are not discussing studio use!) the effect in reality is negligible. Under bad light you wonÄt use a polarizer usually, as it does not show much effect anyway.


Ben

P.S. about IR others have written already more knowledgeable, than I could.

[Snydly]

Just1MoreDave.
Do you mean shoot raw, then convert PP, or set the camera to monochrome?
Thanks...

[Snydly]

Ben Edict,
Thanks for the detailed response. Thanks to all.

Hypothetical situation. A lake, the sun near overhead. I'm facing west on a perpendicular shorline overlooking the lake. The sun is slightly south, say left eleven high, about 60 degrees up from the horizon. Will I get different results from a pl or cpl filter when looking into the water at my right two oclock, and my left 10 oclock? From what you wrote, and others too, it seems the angle of the reflected light into the lens may cause different results. Is that true? I will go test my questions, but I'm trying to understand the function of the polarizer. The photo's above are great, but my polarizers get darker when removing reflections. I have a couple that have marks on them that I would think indicate 'up', but they seem to work better when at 90 degrees on the lens. That's what lead to my confusion.

Thanks...

[Ben_Edict]

Ben Edict,
Thanks for the detailed response. Thanks to all.

Hypothetical situation. A lake, the sun near overhead. I'm facing west on a perpendicular shorline overlooking the lake. The sun is slightly south, say left eleven high, about 60 degrees up from the horizon. Will I get different results from a pl or cpl filter when looking into the water at my right two oclock, and my left 10 oclock? From what you wrote, and others too, it seems the angle of the reflected light into the lens may cause different results. Is that true? I will go test my questions, but I'm trying to understand the function of the polarizer. The photo's above are great, but my polarizers get darker when removing reflections. I have a couple that have marks on them that I would think indicate 'up', but they seem to work better when at 90 degrees on the lens. That's what lead to my confusion.

Thanks...

These indicator marks are are intended to point at the sun for max. effect if you shoot at the textbook 90 deg. to the sun. Not all polarizers have these. And the max. effect is very dependent on your shooting angle to the sun, so the indicator's position aiming at the sun is not the final rule. Its main purpose is a very simple one: If you hold the pol filter in froint of your eyes and turn it, until you like the effect, just look at the indicator's position and place it in front of your camera with the indicator in the same position. This is about the only way to use a pol filter with rangefinders...

There is a nice write-up in Luminous Landscape. BUT there is the usual urban myth, that DSLRs would need the CPL version. I don't know, who started that myth (maybe the makers, as they earn more money with CPLs...). But otherwise the article is nice: Polarizers

Ben

[Jewelltrail]

I want to expand a bit on polarizers. Technicallities first:

A polarizer will reduce reflections on non-metallic surfaces, i.e. on all surfaces that are not conductive, by removing those parts of the light which are polarized at an 90 deg angle to the polarizer's own pass-through-angle. You can imagine a polarizer to be a simple fence with parallel rods. Only the light passes through the fence which oscillates parallel to the fence rods, whereas light perpendicualr to the rods will be stopped by the fence.

1. polarizers only work noticeably, when there is polarized light! That means, that on dull, foggy, misty etc, days, they won't show much or any effect at all.

2. on sunny days with clear skies, a large proportion of the sun light is polarized. On these days a polarizer works best. It removes a large proportion of the polarized light and thus the blue sky gets darker. On esuch a day foilage, water surfaces etc. will also reflect a large amount of that naturally polarized sun light and that can be removed with the polarizing filter.

You will then see an increase in saturation of greens etc. And you may be able, to look through the water surfgace and see the sand and pebbles etc. on the ground, which otherwise would be hidden by the reflecting water surface.
The same effect works with glass windows, if you place the polarizing filter at an agle with the glass and the incoming light.

3. polarizers have no officially "correct" position (they are no politicians…) You need not use them at full throttle. Sometimes just a slight application looks much better, because removing too much reflectios on foilage and achieving a really dar blue sky simply looks unnatural.

With the rotating filter mount, it is easy to find a pleasing position.

4. Circular versus Linear Polarizing Filters: As Mike Cash and Just1MoreDave have already written, there is in most cases no real need for a CPL.

A linear polarizer will only affect camera exposure meters, when they are located behind a secondary mirror (split beam mirrors), which was mainly the case with some film cameras like the Pentax LX. In our Pentax DSLRs the meter cell is located in the prism housing (a very traditional design) and is thus not affected by the polarization, that such a split-beam mirror introduces. A polarizing split-beam mirror + a linear polarizing filter would irritate the exposure system massively.

What can be affected is the AF sensor. But not by giving fals reading (and off focus), but only, because a linear polarizer would let much less light through to the AF sensor, than a CPL. That means, the AF sensor may stop working with a linear polarizer, under not so bright light.

BUT as a polarizer mainly makes sense (see above) for use under bright sun light (we are not discussing studio use!) the effect in reality is negligible. Under bad light you wonÄt use a polarizer usually, as it does not show much effect anyway.


Ben

So, buy the best polarizers, but buy linear ones--this is what I take from all this, something I learned from research a while back, though I wish I found Ben's explanation first--would have saved me a lot of time and I would have come away with a much better understanding.

Ben Edict: In our Pentax DSLRs the meter cell is located in the prism housing (a very traditional design) and is thus not affected by the polarization, that such a split-beam mirror introduces.

I also read other DSLR makers were affected negatively by a LP, because their metering systems differ from the Pentax DSLR design. Does anyone know if this is true?

[Graystar]

I use a linear polarizer on mine.
What did I miss by not paying four times as much money for a circular polarizer?

Pentax has confirmed that both linear and circular polarizer work properly with Pentax digital SLRs.

As I'm not a filter dealer, I can't be 100% certain, but as far as I know only B+W makes a multi-coated linear filter. The 58mm is about 88 bucks, while their 58mm circ. pol. is 92 bucks.

So unless you have a B+W Linear MRC filter, you're missing reduced reflections, and the best possible light transmission.

[Just1MoreDave]

Just1MoreDave.
Do you mean shoot raw, then convert PP, or set the camera to monochrome?
Thanks...

I don't think there's any reason to not use RAW, even if you want a monochrome image. (I guess the preview image might be easier to see.) Exposure is still tricky and you might need the extra range for PP.

[Graystar]

Pentax has confirmed that both linear and circular polarizer work properly with Pentax digital SLRs.

Well here's an interesting development. I received a second response to my question to Pentax.

I had send a message to Pentax asking about metering with a polarizer on their their digital SLRs. I received this reply...

Thank you for contacting Pentax.

Either will work fine.

If you are in need of further assistance, please respond to this email
or call our technical support center at 800-877-0155.

Sincerely,
Dorian B.
Pentax Imaging Technical Support

But just now I received another message, which was made as a response to the Dorian B.'s message...

Greetings,

While a linear polarizer may not affect the metering,a circular
polarizing filter is strongly recommended since a linear polarizer may
interfere with the autofocus system.

Thanks,

Mark Davis Product Specialist

So as Ben Edict had noted, Pentax also raised a concern about the autofocus system. Personally, bright sun isn't the only time I've used my polarizer. It works well to cut reflections in water, and when you're trying to photograph Koi, you need all the light you can get. So I still say it's best to get a circular polarizer with an SLR.

[Jewelltrail]

I am happy with the performance of my LPs on my autofocus glass--metering and autofocus are not negatively affected.

[Mike Cash]

Pentax has confirmed that both linear and circular polarizer work properly with Pentax digital SLRs.

So nice that they confirm what I already knew from personal experience.

As I'm not a filter dealer, I can't be 100% certain, but as far as I know only B+W makes a multi-coated linear filter. The 58mm is about 88 bucks, while their 58mm circ. pol. is 92 bucks.

So unless you have a B+W Linear MRC filter, you're missing reduced reflections, and the best possible light transmission.

My linear cost about fifteen bucks. The cheapest circular in the shop (same size) was about sixty bucks. For me that means the difference between owning a polarizer or not owning a polarizer.

Some of us do manage to struggle along somehow without the absolute "best" equipment.

[Ben_Edict]

So nice that they confirm what I already knew from personal experience.

My linear cost about fifteen bucks. The cheapest circular in the shop (same size) was about sixty bucks. For me that means the difference between owning a polarizer or not owning a polarizer.

Some of us do manage to struggle along somehow without the absolute "best" equipment.

We often can find an older linear polarizer of a top brand for the same or less than a soso circular polarizer. For instance I could get a B+W LPL for considerably less than even a lowly Cokin circular one. So even if you pay nearly the same for a linear pol, you often get more quality.

Ben

[Jewelltrail]

Ben Edict: A linear polarizer will only affect camera exposure meters, when they are located behind a secondary mirror (split beam mirrors), which was mainly the case with some film cameras like the Pentax LX. In our Pentax DSLRs the meter cell is located in the prism housing (a very traditional design) and is thus not affected by the polarization, that such a split-beam mirror introduces. A polarizing split-beam mirror + a linear polarizing filter would irritate the exposure system massively.

Here is what it says on the back of my Linear Polarizer case, and I quote, verbatim:


"Linear Polarizer filters should not be used on camera bodies with a polarizing half mirror (split beam metering). A Circular Polarizer is recommended for these cameras."


Ben, as usual, is spot on!

[Ben_Edict]

Here is what it says on the back of my Linear Polarizer case, and I quote, verbatim:


"Linear Polarizer filters should not be used on camera bodies with a polarizing half mirror (split beam metering). A Circular Polarizer is recommended for these cameras."


Ben, as usual, is spot on!

Thanks for the compliment. But as my chemistry teacher used to say: I don't know much more than you - but I know where I can look-up everything… So, I have a large libraray of specialised text books in my cupboards at hand…

Ben

[Oggy]

Well done for getting it right Ben.

Some of the previous replies had me rolling on the floor.