circular vs standard polarizing filter

Started Dec 11, 2003 | Discussions
OzRay
OzRay Forum Pro • Posts: 19,428
circular vs standard polarizing filter

Can anyone recommend which polarizing filter is best for the A1 - circular or standard and why? Thanks

Ching-Kuang Shene
Ching-Kuang Shene Veteran Member • Posts: 6,359
Re: circular vs standard polarizing filter

OzRay wrote:

Can anyone recommend which polarizing filter is best for the A1 -
circular or standard and why? Thanks

A linear one would be sufficient unless you will also use it with a SLR or DSLR camera.

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

 Ching-Kuang Shene's gear list:Ching-Kuang Shene's gear list
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OzRay
OP OzRay Forum Pro • Posts: 19,428
Re: circular vs standard polarizing filter

Ching-Kuang Shene wrote:

OzRay wrote:

Can anyone recommend which polarizing filter is best for the A1 -
circular or standard and why? Thanks

A linear one would be sufficient unless you will also use it with a
SLR or DSLR camera.

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

That's interesting, because I've always used a standard one with my SLRs. That's what I'm curious about, seeing as they sell the two types for digital cameras. I've tried to do an Internet search, but have not come up with an explanation. What's the difference between the two (other than one costs more)?

ECCL Contributing Member • Posts: 638
Re: circular vs standard polarizing filter

There is a good explanation of the difference between Linear and Circular polarizer from the following site:

http://www.thkphoto.com/products/hoya/gf-04.html

Regard,
Eccl

OzRay wrote:

Ching-Kuang Shene wrote:

OzRay wrote:

Can anyone recommend which polarizing filter is best for the A1 -
circular or standard and why? Thanks

A linear one would be sufficient unless you will also use it with a
SLR or DSLR camera.

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

That's interesting, because I've always used a standard one with my
SLRs. That's what I'm curious about, seeing as they sell the two
types for digital cameras. I've tried to do an Internet search, but
have not come up with an explanation. What's the difference between
the two (other than one costs more)?

Ching-Kuang Shene
Ching-Kuang Shene Veteran Member • Posts: 6,359
Re: circular vs standard polarizing filter

OzRay wrote:

That's interesting, because I've always used a standard one with my
SLRs. That's what I'm curious about, seeing as they sell the two
types for digital cameras. I've tried to do an Internet search, but
have not come up with an explanation. What's the difference between
the two (other than one costs more)?

If you search DPreview, you will come up with so many posts answering this question, including a few of mine. A complete answer is very simple, but technical. However, I'll try to answer it is a non-technical way.

Some cameras have beamspliter or some device that can split the light coming through the camera lens to various components such as viewfinder, light meter and AF system. The splitting ratio has to be constant for all components that receive the split light to work properly. For example, just an example, the incoming light may be split 50% to viewfinder, 20% to meter and 30% to the AF system. The meter will measure this 20% incoming light for determining exposure value (EV).

If a linear polarizer is used with this system, due to the "phase" of the polarized light, the constant split ratio cannot be maintained. In other word, 60% may go to the viewfinder, 15% to meter and 25% to the AF system. Thus, the meter, which does not know the split ratio has been changed, will use this 15% for exposure value determination. Since the incoming light is 5% less than the supposed amount, the metering system will believe the illumination is 5% weaker and may increase EV to counter balance, which means a larger aperture or slower shutter speed will be used. Consequently, the scene will be over-exposed. On the other hand, the AF system may need certain amount of light (e.g., F5.6) for the AF mechanism to work properly. Now, the reduction of 5% (from 30% down to 25%) may cause the light that is available to the AF system to use may drop below the minimum needed amount, and the AF system may fail to operate.

A circular polarizer will readjust the polarized light by the linear one so that the beamspliter will keep the splitting ratio constant.

Since consumer digicams do not use beamspliter and its equivalent, consumer digicams can use linear polarizers. Since SLR/DSLR cameras do have beamspliters, they cannot use linear polarizers due to the above mentioned reason.

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

 Ching-Kuang Shene's gear list:Ching-Kuang Shene's gear list
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OzRay
OP OzRay Forum Pro • Posts: 19,428
Re: circular vs standard polarizing filter

Ching-Kuang Shene wrote:

OzRay wrote:

That's interesting, because I've always used a standard one with my
SLRs. That's what I'm curious about, seeing as they sell the two
types for digital cameras. I've tried to do an Internet search, but
have not come up with an explanation. What's the difference between
the two (other than one costs more)?

If you search DPreview, you will come up with so many posts
answering this question, including a few of mine. A complete
answer is very simple, but technical. However, I'll try to answer
it is a non-technical way.

Some cameras have beamspliter or some device that can split the
light coming through the camera lens to various components such as
viewfinder, light meter and AF system. The splitting ratio has to
be constant for all components that receive the split light to work
properly. For example, just an example, the incoming light may be
split 50% to viewfinder, 20% to meter and 30% to the AF system.
The meter will measure this 20% incoming light for determining
exposure value (EV).

If a linear polarizer is used with this system, due to the "phase"
of the polarized light, the constant split ratio cannot be
maintained. In other word, 60% may go to the viewfinder, 15% to
meter and 25% to the AF system. Thus, the meter, which does not
know the split ratio has been changed, will use this 15% for
exposure value determination. Since the incoming light is 5% less
than the supposed amount, the metering system will believe the
illumination is 5% weaker and may increase EV to counter balance,
which means a larger aperture or slower shutter speed will be used.
Consequently, the scene will be over-exposed. On the other hand,
the AF system may need certain amount of light (e.g., F5.6) for
the AF mechanism to work properly. Now, the reduction of 5% (from
30% down to 25%) may cause the light that is available to the AF
system to use may drop below the minimum needed amount, and the AF
system may fail to operate.

A circular polarizer will readjust the polarized light by the
linear one so that the beamspliter will keep the splitting ratio
constant.

Since consumer digicams do not use beamspliter and its equivalent,
consumer digicams can use linear polarizers. Since SLR/DSLR
cameras do have beamspliters, they cannot use linear polarizers due
to the above mentioned reason.

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

Excellent. Thanks guys.

John down under Veteran Member • Posts: 8,238
Re: circular vs standard polarizing filter

OzRay wrote:

Can anyone recommend which polarizing filter is best for the A1 -
circular or standard and why? Thanks

My A1 is almost within my grasp and I am looking for a polarising filter. I phoned a camera store today where the salesman sounded knowedgeable and stated that circular polarisation would be necessary for the A1 so as not to interfere with the AF system. Has your research uncovered anything to confirm or dispute that claim?
Cheers from down under (also), John

Josh Halberthal Regular Member • Posts: 218
Re: circular vs standard polarizing filter

That is the best explanation that I read so far. Thanks!
Josh

If you search DPreview, you will come up with so many posts
answering this question, including a few of mine. A complete
answer is very simple, but technical. However, I'll try to answer
it is a non-technical way.

Some cameras have beamspliter or some device that can split the
light coming through the camera lens to various components such as
viewfinder, light meter and AF system. The splitting ratio has to
be constant for all components that receive the split light to work
properly. For example, just an example, the incoming light may be
split 50% to viewfinder, 20% to meter and 30% to the AF system.
The meter will measure this 20% incoming light for determining
exposure value (EV).

If a linear polarizer is used with this system, due to the "phase"
of the polarized light, the constant split ratio cannot be
maintained. In other word, 60% may go to the viewfinder, 15% to
meter and 25% to the AF system. Thus, the meter, which does not
know the split ratio has been changed, will use this 15% for
exposure value determination. Since the incoming light is 5% less
than the supposed amount, the metering system will believe the
illumination is 5% weaker and may increase EV to counter balance,
which means a larger aperture or slower shutter speed will be used.
Consequently, the scene will be over-exposed. On the other hand,
the AF system may need certain amount of light (e.g., F5.6) for
the AF mechanism to work properly. Now, the reduction of 5% (from
30% down to 25%) may cause the light that is available to the AF
system to use may drop below the minimum needed amount, and the AF
system may fail to operate.

A circular polarizer will readjust the polarized light by the
linear one so that the beamspliter will keep the splitting ratio
constant.

Since consumer digicams do not use beamspliter and its equivalent,
consumer digicams can use linear polarizers. Since SLR/DSLR
cameras do have beamspliters, they cannot use linear polarizers due
to the above mentioned reason.

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

Lemuel Fillyaw Regular Member • Posts: 135
Thats what I....

thought. I have always been under the impression that if any camera Digital or otherwise had an auto focus system that you will need a circular. I have seen AF cameras that used a linier and the AF system , for lack of a better term, messed up and had to be repaired. I would check with Minolta. But I'll be picking up a circular just in case.

Lem

toughluck Veteran Member • Posts: 3,748
Re: circular vs standard polarizing filter

Unless you plan to buy a (d)SLR camera with a beam splitter (semi-transparent mirror), don't bother buying the circular polariser.

Linear polarisers give much more possibility of creative work. Circular polarisers image change varies very little between various degrees.

Why a linear polariser won't 'hurt' your exposure, AF, nor final picture? Because a sensor actually records what it sees through the lens without any beam splitter, or anything similar. AF, light metering, et al, are done with the actual recorded image off the sensor instead of specialised sensors. The talk that 'circular polarisers work with digital cameras, and linear work with film ones' is absolute rubbish. A linear polariser won't work with a film camera that:

  • has AF and AE;

  • has a lens attached that turns its front element for focusing;

  • does not have TTL viewfinder.

The only thing that has been overcome so far is using circular polarisers with rangefinders, by adding a simple device that swings the polariser up and down to see its effect in the viewfinder. Even though it is much better than actual RF unpredictability, it's still not great.

That's wy for all those cameras, circular polarisers have been recommended over and over.

Actually, linear polarisers suffered when automatic SLRs became dominant enough to render lin-pols next to obsolete, or at least uneconomical to make in large quantities, and it was until digital era that linears had their renaissance, thanks to their lower price, higher creative value, (usually) better image quality, and the unnecessity of cir-pols. There is a multitude of sellers that push out "circular polarisers designed specifically for digital cameras" - there's no such thing. Light polarised parallel (through a linear polariser) is better received and perceived by the sensor than circularly polarised (which may hit sensor at high angles of incidence).
I do hope you understand what I've written here.
OzRay wrote

Can anyone recommend which polarizing filter is best for the A1 -
circular or standard and why? Thanks

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Tortellino Senior Member • Posts: 1,330
Some people will never believe...

John down under wrote:

I phoned a camera store today where the salesman sounded
knowedgeable and stated that circular polarisation would be
necessary for the A1 so as not to interfere with the AF system.

...despite all the theoretical explanations (including this thread) and practical experiences. What is it going to take to prove that linear polarizers work fine on these cameras? I suppose nothing short of eliminating all the pseudo-knowledgeable (or just arrogant) salespeople, whose only interest is to sell you the most expensive equipment they can.

Please, everyone who "heard that CPs are necessary for all autofocus cameras", but does not not why, stop spreading this disinformation, and read up on the suject before making your next comment. A search for Linear Polarizer will bring plenty of threads on this forum.

T.

Victor Bos Regular Member • Posts: 292
Re: circular vs standard polarizing filter

John down under wrote:

OzRay wrote:

Can anyone recommend which polarizing filter is best for the A1 -
circular or standard and why? Thanks

My A1 is almost within my grasp and I am looking for a polarising
filter. I phoned a camera store today where the salesman sounded
knowedgeable and stated that circular polarisation would be
necessary for the A1 so as not to interfere with the AF system. Has
your research uncovered anything to confirm or dispute that claim?
Cheers from down under (also), John

Well, apparently your salesman is not knowledgeable at all, because he is wrong....

Victor.

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http://www.victorbos.com/ -Nature photography (dutch)

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twinpot Regular Member • Posts: 353
The linear (cheap) one works

OzRay wrote:

Can anyone recommend which polarizing filter is best for the A1 -
circular or standard and why? Thanks

Well, it works fine on my A1

John down under Veteran Member • Posts: 8,238
Thanks T, V and tl for the 'real' truth.

T, Victor and toughluck,

Thanks for putting this thing to bed. I'm glad I posted what the salesman said as much to confirm the truth as anything else, even though as you point out this subject has been covered previously. I only just started looking at circular polariser information and started with phoning some shops. I could equally have started with the internet and that was going to be my next step (which it now has been to some extent). I'd like to think the salesman was simply mistaken rather than deliberately lying. Either way, that was the first time I had spoken to him or anyone else in his shop and I will be more cautious if I deal with him in future. I'm going to ask the same question of my A1 salesman (who has been fantastic) when he is back at work. I hope he doesn't disappoint me about his advice on the whole polariser thing, but I'll remain optimistic.

Cheers from down under, John

Ching-Kuang Shene
Ching-Kuang Shene Veteran Member • Posts: 6,359
Re: circular vs standard polarizing filter

I am just curious why this linear vs. circular polarizer discussion can go on and on for days, weeks, months, and even years. Now, I know why. The answer was provided IN this thread 10 days ago here:
http://forums.dpreview.com/forums/read.asp?forum=1024&message=6913931

and people still raise the same question without going through the previous posts IN the same thread. Is it funny?

CK

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