The Circular Polarizing Filter

[marc]

The Circular Polarizing Filter

All photo samples are untouched, only resized and optimized for the web.

(This post was updated September 30, 2004)

A filter that typically screws onto the end of your existing lens. This filter is appears to be a single piece, and when screwed onto the lens, the top portion of the filter still turns to adjust the amount of effect.

By turning the filter, you would see thought the view finder a change in the light in your scene.

Reduce glare off of reflective surfaces like water and window panes. I find this handy for reducing post editing of reflections on classic car photography.

This filter is a good standard tool for outdoor photographers on those bright lit sunny days, and can add depth and more contrast to clouds and other elements in your scenes.

Here is a before and after demonstration on clouds. It makes them richer in color, and deeper in contrast, also better balancing the exposure.



It will tend to slow your shutter speed down just a bit, but on a brightly light sunny day, your potential shutter speed would so high, it would likely not be a concern.

Here's an example the Circular Polarizing Filter on a lake.

Before


After, through the viewfinder, I could see what is on the lakebed below. Also notice the clouds in the background and the island on the horizon both have more depth and definition.


Next, here is how it's works on a glass surface (courtesy your grocer's freezer section). It doesn't have as much effect at a 90 degree angle, but as you can see here, at about 40 degrees, it is very effective.

Before


After

[lcastillo]

thank you for the excellent examples marc

[marc]

From Canon.com

"This type of filter eliminates reflections from glass and water the same way as a circular polarizing filter, but it cannot be used effectively with most auto exposure and autofocus cameras as it will cause exposure errors in AE cameras equipped with TTL metering systems using half-mirrors, and will cause focusing errors in AF cameras incorporating AF rangefinding systems using half-mirrors".

[nighs]

Great examples Marc. Thank you.

[Annie]

Thank you, Marc, very effective examples!

Question, why have they always (pre-digital) seemed to lack click stops? I remember back when, and am wondering to this day!

(Click stops as in vs. spinning freely.)

Annie

[gurlskout]

that last one! WOW! Such a difference!!!

[TravlynVicki]

Thank you Marc, for these examples and the explanation of the linear polarizer. I looked at these when you posted the link in our current Cnet photography course - even (gulp), missed a critical aspect of the circular polarizer which explained why I cobbled a recent photo while using it (forgot to turn it - and I knew better), which needed more reflection removed.
Thank you again . . . time to get back outside with my camera and lenses - I have a perfect location on a mirror-smooth lake surface to REALLY take my time and explore my camera settings with.

Vicki

[Otto]

Back to the question of the term "circular". The guy in the store where I bought my "circular polarizing filter" told me that "circular" refers to the fact that the filter can be rotated to cancel certain orientations of light rays entering the lens system. For example, in Marc's pics, the cloud shot would have cancelled horizontal rays, and the freezer shot would have cancelled vertical rays. This implies that Marc rotated the filter to produce the desired effect, right? Having tried the same thing myself, and achieving the same or similar results, my question is: "what is a linear polarizing filter?". And why, or indeed when, would one want to use a linear polarizing filter?

I seem to think that "linear" would mean either horizontal or vertical, or some other angle in between, and "circular" would mean just that, ie: any angle of incidence, negating any useful effect to be derived from the filter.

I am probably missing something here. Any comments?

[lenah]

Man, there are so many basic things I had no clue of! Thanks for all the info!

I have a question: Would the circular polarizer filter make any difference on outdoor close up shots?

[marc]

No one usually uses it for Macro (close up) shots.

[Otto]

I seem to have answered my own questions at the web site:

http://dpfwiw.com/polarizer.htm

There appears to be a very important difference between linear and circular when the exposure metering mechanism uses split beam, like in film TTL metering. For my camera (Panasonic FZ20) it makes no difference at all! I would submit that most (if not all) digital cameras do not need "circular". I seem to think that the linear polarizing filter is the better option for digital cameras because they are 1)less expensive, and 2)there are fewer layers of filter material to distort and degrade the incident light. (Pity I purchased the "circular" before I knew this!).


To UV or not to UV? Try this site for an interesting discussion:

http://www.photo.net/equipment/filters/

I shall continue using my UV filter for lens protection (only!).

[Pete H]

Otto is correct. Both linear and circular polarizing filters work the same when you are considering the light coming into the camera. Both let you rotate the filter to line up with (or most likely, perpendicular to) polarized light coming to the lens. The difference is the kind of light that comes out the camera side of the filter. The light that has passed through a linear polarizer is (what else) linearly polarized. It should work fine going through lenses and activating the digital image sensor (i.e. all those megapixels). <b>On the other hand,</b> if anywhere in the light path the light has to bounce off a partial mirror, linearly polarized light does weird things. In particular, if such a mirror is used to bounce light to a light meter, optical view finder, range finder, etc, you won't get correct results with a linear polarizer. If your camera doesn't have such mirrors, the linear polarizer can be used with no problem.

The light that exits a circular polarizer is (as you might expect) circularly polarized light. This can reflect off partial mirrors the same as ordinary light. Thus if your camera has such mirrors in its light path, you can use a circular polarizer with no problem.

<b>Note:</b> I don't know the internals of most digital cameras, but my understanding is that digital SLR cameras are more likely to have such mirrors, and digital viewfinder cameras probably do not. The actual details undoubtedly depend on brand and model.

<b>OK, what exactly does a polarizing filter do?</b> To answer that we have to know what polarized light is. And for that, we need to know that ordinary light vibrates in all directions (up and down, left and right, and in all directions in between). When light reflects off something non metallic at an angle (think glass pane or tiny dust particles of the sort that make the sky blue), the light vibrating in some directions is absorbed, while the remaining light that is reflected is vibrating in the perpendicular direction. We call this light that vibrates in only certain directions <i>polarized light</i>.

Now a polarizing filter blocks light that vibrates in some directions while it lets through light vibrating in other directions. Marc's wonderful examples show how the filter affects a picture. For instance, the light coming from the blue sky at an angle to the sun is polarized. When you rotate the filter to block the polarized light, the blue part of the sky gets darker. Light reflected from the clouds is not polarized, so it passes through the filter in much greater proportion than the sky light (though the filter does remove a lot of the light from a non-polarized source, much like a neutral-density filter), so the contrast is increased and the cloud structure stands out. When you shoot at an angle through glass or the surface of water, you can use a polarizer to block the light that is being reflected from your side of the surface to the camera; that lets the camera see clearly what is on the other side of the surface.

If there is no polarized light in the subject you are photographing, a polarizing filter will just remove a certain amount of the light uniformly (again, like a neutral-density filter); that can allow you to use a longer exposure or a wider f-stop, but it will do nothing to block or emphasize one part of the light compared to another. If the light in the scene is not polarized, rotating the filter will make no difference. If that's all you are trying to accomplish, neutral-density filters are much less expensive.

Another use of a polarizing filter is to block light that you have artificially polarized. If you put a vertical polarizing filter in front of your flash and a horizontal filter in front of your lens, you can shoot directly into a glass surface and not see the reflection of the direct flash.

Oh, someone asked about click stops on polarizing filters. I can't see why you would want them. The light might be polarized at any angle, so it seems you would want to be able to set the filter to any angle, not be limited to some fixed pre-set angles.

(Hope you don't mind this somewhat lengthy essay. Thanks for reading; hope the explanation helps.)

[Frederick A. MacKinnon]

Marc and Pete,

Thank you so much for the very definitive essays. I guess I'm still wondering a bit about what to do as a newbie. My camera is a Kodak DX7590. Of, course it's not a Digital SLR and the megapixel is 5.0.

Is there much difference in price between the circular and linear polarizer?

Is there any reason to buy first a linear polarizer, learn a few things, and then step-up to a cirular polarizer, or does the circular do all and more that the linear can do.

There are no camera shops nearby, the closest being about 75 miles south.

I'm getting ready to make the trip soon and I'm leaning toward a circular polarizer based on your excellent essays. Any futher comments or suggestons from anyone would be most helpful. Thanks.

Fred

[Pete H]

...

Is there much difference in price between the circular and linear polarizer?

Is there any reason to buy first a linear polarizer, learn a few things, and then step-up to a cirular polarizer, or does the circular do all and more that the linear can do.

...

Fred

A <u>very</u> brief look on Google/Froogle implied that everything else being equal, a circular polarizing filter probably costs from 50% to 100% more than a corresponding linear polarizing filter.

One earlier poster (I forget who) suggested that the greater internal complexity of the circular filter might lower picture quality more than a linear filter would. (Of course every piece of glass between the sensor and the subject degrades the image somewhat; the hope is that the function being performed makes up for that effect.) I suspect that if you have a filter of good quality, any theoretical difference would be minimal.

The <b>only</b> difference in function between the 2 types is that the linear polarizing filters will not work correctly in certain cameras. If it works fine in yours, there is no advantage to getting the more expensive circular polarizer. If a linear polarizer doesn't work properly with your camera, there is no point in getting it. The problems will show up in bad exposure and possibly bad focusing.

If you are in a shop, try out the filter. Try pictures at an angle (i.e. not straight in) into a display cabinet. See if there are exposure problems. If they have both kinds of filters, try both on your camera and see if you can see any difference in the pictures. Do make sure you are using the filters in circumstances where they have some polarized light to filter (like the display cabinet or at an angle to a window.) You should be able to rotate the filter until it blocks most of the glare that is being reflected from the glass. If the price difference is not a consideration, especially if you can't try it with your camera, the circular polarizer might be a safer choice.

[Frederick A. MacKinnon]

Thanks, Pete! Very helpful indeed. I'm going to review all that was written and look again at the links too. I'll certainly take my camera with me and I assure you, they WILL let me try them out. That's just the way I am: a gentle but very firm customer. LOL

Best regards,
Fred

[marc]

Like any filter, you need to buy quality glass if you're going to put anything on the front of your lens.

[TwilightMyst]

I'm glad I read this...
Thanks for the tips everyone!!

[jlewis3555]

The only problem I have with a circular filter is not getting my fingers in the way lol After reading this I went and bought a circular filter it improved the quality of my photos by at least 80%. My problem is finding filters, (Ilive in a small town in Uptate New York) and have an 46mm lens which I have found out is not a common size.

Thanks Marc for the tip
Jeff
[

[gentletouch11440]

From Canon.com

"This type of filter eliminates reflections from glass and water the same way as a circular polarizing filter, but it cannot be used effectively with most auto exposure and autofocus cameras as it will cause exposure errors in AE cameras equipped with TTL metering systems using half-mirrors, and will cause focusing errors in AF cameras incorporating AF rangefinding systems using half-mirrors".

I found this out myself, when I bought a linear polarizer filter, and some of my shots wouldn't focus correctly. I did find a bit of a solution with my Canon S5 IS. It has a Shortcut Button setting, with several settings, one of which is Automatic Focus. When I use a large aperture, such as 2.7 or 3.5, and the LP filter, when I center the subject I press the shortcut button to add a more secure focus, then I press the trigger halfway down, and it usually does a great job of focusing, even when zooming the lens.

I'm buying a circular polarizing filter soon, though. I want both along with me.

[glennie]

I bought a circular polarizing filter and new nothing about how it is supposed to work, just played with it and it was hit and miss with the success rate... so this has been a fantastic insight for me. Thanks Marc and Pete expecially.

I have a question which I hope isn't too dumb how can you determine which direction the polarized light is coming from and how does that relate to the little notch on the Hoya filter I have.

[ksuwalleye1]

I haven't paid that much attention to the notch on mine. I usually just frame the shot using the LCD and then rotate the filter until I get the degree of polarizing I like the best.

[Otto]

. . . how can you determine which direction the polarized light is coming from . . .

Hi Glennie, I haven't browsed this forum for quite some time, so: welcome aboard!

Regarding your question, generally, horizontal surfaces reflect horizontally polarised light, and vertical surfaces reflect vertically polarised light. This is most noticable when the main light source is somewhere more to the front of the camera.

There is no strict rule on how to set your filter. depending on whether you want to restrict or emphasise the reflected light, you adjust the filter accordingly.

I have noticed that when the camera is set to auto anything (apperture, shutter speed, or both) it is quite difficult to adjust the filter properly because the camera will adjust the exposure for optimum, average light, thereby reducing the filter's effect.

The best way to set the filter (I've found) is to set the camera to fully manual, adjust the exposure for a suitable image, then turn the filter to get the desired effect. Now make any final exposure adjustments and "shoot away".

The reflected light is not always exactly horizontal or vertical, but most times at some other angle. So I don't rely on "clicks" or other marks on the filter. My best gauge for the desired shot is my own eyesight.

Hope this helps a bit.

[glennie]

Thanks Otto - that helps me a lot. I thought the notch might be a guide until I 'get my eye in'. And after reading all this very useful information again I hope you don't mind another question... I would also like to understand if you turn the filter to diminish the effect of polarising the light and it acts as a neutral density filter what purpose does that serve?

[Otto]

. . . acts as a neutral density filter what purpose does that serve . . .

Although I've heard the term, I had no idea what a "neutral density filter" does or what it is used for. You prompted me to go find out:

Wikipedia says:
http://en.wikipedia.org/wiki/Neutral_density_filter

But I think this link says it very well:
http://digital-photography-school.com/b ... ty-filter/

Food for thought - and more projects to experiment with. Especially getting the blurred effect of waterfalls in bright sunlight.

I look forward to some of your samples.

[Barendjr]

Having seen some of the wonderful shots taken by other members of the forum with a polarising filter - I went out and bought one last weekend.

without filter

reflectons off my front windows are obvious.

with filter


Reflections eliminated with a clear view through the windows into the living room.

Gotta try this on the sky next !

[grothause]

Okay I was looking at these on amazon.com and since I don't know anything, what price range is appropriate? They have one for as little as $18, but as much as over $100. Is there a brand known for excellent quality but reasonable price?

[ksuwalleye1]

I read a fair amount on these, but that was a few years ago. I got my Cokin 58mm CP filter at Best Buy and I recall giving about $30 US for it. I have no complaints with it at all.

[marc]

Hi Beth,

You're putting more glass on the end of a lens, so it should be a good piece of glass. Good optics are key to good photos. I'd go half way at around $50.

You want one that is multicoated to handle light better.

For anyone using L series professional lenses, I'd suggest B+W brand Circular Polarizing Filter.

[grothause]

Thanks, that was what I was thinking, but wasn't sure. There is just so much stuff out there it is confusing to me