Polarizers or not - Test Images

[AlwaysOnAuto]

As you can see from the photos of the car, Geoff, there weren't any shadows at all. Very overcast, thick marine layer that never really burned off. Made it hard to get things to 'POP'.

[Mike Buckley]

Geoff,

You started this thread largely as an outgrowth of posts in Brian's thread in which you and I disagreed about what a polarizing filter does and does not do. I have not been available to respond earlier to your new thread and may not be able to participate much other than writing this post.

The crux of what a polarizer does and does not do is entirely explained by the physics of light. The importance of that is to recognize that when all of us use a polarizer effectively in the same conditions, we will all get generally the same results even when the equipment we use varies.

There are lots of explanations available on the Internet about the results we should expect to get when using a polarizer. Some of them are accurate and some are not, including explanations in the threads here at CiC. To avoid confusion, I recommend the book, Light: Science & Magic. Now in its fifth edition, it explains the physics of science relating to using a polarizer in lay terms that even I can understand. More important, I've never seen anyone refute anything in the book, which explains why I and others consider it sort of like a bible of the subject of light in the context of photography. In short, you can trust the information in that book so much so that when your results vary from what the book leads you to expect, you can begin trying to figure out how to improve your use of polarizers.

The exact same information about using a polarizer is provided word-for-word in the fourth and fifth editions. I wouldn't be surprised to learn that it's the same in the earlier editions. I mention this just in case you find one of the earlier editions at a lower price and want to purchase it for its explanation of how and why a polarizer does what it does.

[NorthernFocus]

Having re-read the OP I guess I'm missing the point. Reference is made to another thread which I didn't see so maybe that's why. Was the OP intended as "here are some examples, I told you so"? Or "here are some examples, what am I missing?"?

[dem]

All reflected light is in a single plane - that's O level physics...

It is not. This statement is only true for reflections from dielectric materials at a single angle:

http://hyperphysics.phy-astr.gsu.edu.../polar.html#c2

[Geoff F]

Having re-read the OP I guess I'm missing the point. Reference is made to another thread which I didn't see so maybe that's why. Was the OP intended as "here are some examples, I told you so"? Or "here are some examples, what am I missing?"?

It was from a post where Brian had been uncertain whether a polarizer would help with some of his lighting problems mostly on botanical subjects.

Yellow Bwells, a slowly falling down bamboo fence + a pineapple plant bg

I had posted a link from that thread but not one linking back to the original question. This new thread was to separate any subsequent discussion from overwhelming the original post.

[rpcrowe]

Intensifying or darkening the sky also adds to the camera's capability to capture the foreground and sky in a single exposure, often reducing or even eliminating the need for a graduated neutral density filter.

Photographers sometimes equate the polarizer with darkening the skies only. However, I used a polarizer shooting in the Hoh Rainforest of Washington State's Olympic Peninsula. Everything was wet and the polarizer reduced or eliminated much of the reflection off the wet foliage, thereby capturing intensified color...

[Stagecoach]

Having re-read the OP I guess I'm missing the point. Reference is made to another thread which I didn't see so maybe that's why. Was the OP intended as "here are some examples, I told you so"? Or "here are some examples, what am I missing?"?

Dan, I think the post was generated from this statement by Geoff following Mikes advice that a polariser would have helped the 'glare' on the leaves of Brians foliage image.

A polarizer will give a darker overall scene, Brian, but won't do anything for strong highlights from reflective surfaces. The effect is much the same as using some negative exposure compensation.

This statement of Geoff's is rather contentious, but, he has shown a 'comparison' example here where he demonstrated that a polariser really did not help this specific situation. I base that it did not really help the situation on the fact that if you put his two shots into PP and equalise the 'overall brightness' of the scene the glare looks very similar in each.

His first two examples are specifically in relation to his advice to Brian regarding Brians image subject.

Perhaps the direction of the thread should be to determine why Geoff's examples (first two) gave that result wrt glare on his subject rather than generalisations of polariser use with references to physics, reference books and blue skies.

[dem]

Intensifying or darkening the sky also adds to the camera's capability to capture the foreground and sky in a single exposure, often reducing or even eliminating the need for a graduated neutral density filter.

There are some limitations of using a polarizer as a substitute for a graduate ND filter or exposure bracketing.

First, the effect of darkening the sky with a polarizer is only about a stop. That's often not enough.

Second, the brightest part of the image is often not the blue sky but the clouds that are not darkened by the polarizer. So darkening the sky will not affect the DR.

But if there are no clouds and you need an extra stop of DR, then indeed a polarizer can be useful.

[Mike Buckley]

Perhaps the direction of the thread should be to determine why Geoff's examples (first two) gave that result wrt glare on his subject rather than generalisations of polariser use with references to physics, reference books and blue skies.

Whether or not that's the most effective course of action probably mostly depends on Geoff's preferred method of thinking things through. I offered Light: Science & Magic as an undisputed source explaining the physics of light mostly in response to Geoff's very generalized statements in Brian's thread that I explained in that thread aren't true. It seemed natural and hopefully effective to respond to incorrect generalized statements with the generalized science that explains why they're not true.

[Mike Buckley]

Geoff,

I believe there are only two issues you've raised that might still not have been answered thoroughly enough.

I wonder what sort of light was involved, particularly the car shots which seem rather 'flat' to me. It seems like it was a rather diffused somewhat dull light while I was shooting in full sun.

Light: Science & Magic explains that whether the light is diffuse or not is not a factor. Instead, it's whether the surface being photographed generates a polarized direct reflection. If so, the polarizing filter will impact it. Otherwise, the filter will have no impact. Indeed, the sure-proof way of determining whether the reflection is polarized is to determine if the polarizing filter affects it. The book provides a better and more thorough explanation.

As for my anecdotal experiences, I have used a polarizing filter in a narrow canyon in late afternoon when the sky was nothing but grey clouds and the only light entering the canyon was diffused by the clouds. (Even if the sky had been cloudless, the canyon was so narrow and the sun was so low that no direct light would have entered it.) I have also used the filter outdoors in direct light without a cloud in the sky. Over the decades, the polarizing filter has always had the same effect both indoors and in my makeshift studio whether used in completely diffuse light, partly diffuse light or direct light.

Can a polarizer change the minimum focusing distance for a close up shot? The landscape scenes do not show any difference in sharpness between using a polarizer and not using one...I haven't tried moving back a little to see if that makes any difference for closer work.

Light: Science & Magic doesn't bring up the subject of focusing or focus distance. Bear in mind that considerable information in the book is devoted to tabletop photography and the situations when a polarizing filter will or will not affect the reflection. My hunch is that if any one of the three authors had experienced a noticeable difference when focusing and using a polarizing filter in any circumstance, that information would have been included in the book.

My closest focusing distance when also using a polarizing filter was done using a 90mm macro lens at a magnification ratio of about 1:1.6 to make the photo shown below. I manually focused before mounting the polarizer because the larger amount of light entering the lens made it easier to accurately focus. After mounting the polarizer, it performed exactly as I expected in that focus was not affected but the direct reflection I was hoping to eliminate was indeed eliminated. Other experiences I've had when using lesser magnification ratios of relatively small subjects yielded the same results.

[Stagecoach]

Firstly, it was circular polarizers which was set to the darkest effect in all cases.

Geoff,

Are you certain that your filter is a 'Circular' Polarising Filter and not a Circular 'Linear' Polarising Filter?

If it's a Circular 'Linear' Polarising Filter you will be able to see the darkening affect as you rotate it when viewed from both sides.

If it's a 'Circular' Polarising Filter you will only be able to see the darkening affect as you rotate it when viewed from the camera side.

Just a thought as to your test findings.

[NorthernFocus]

This discussion is largely nonsensical. Polarizers are no panacea. They remove some reflections and not others. For example when shooting across water they will remove some of the reflection/glare but not all of it. They remove reflected light off of some surfaces and not others. They remove reflected light some angles and not others. It depends on how the form of the light is changed when reflected and how that effects whether it passes through the polarizer or not. For that matter, the conventional wisdom of shooting at 90 degrees to the sun is specific to those conditions. Some of the most dramatic effects with polarizers are when there is no direct sunlight such as shooting a waterfall in a deep canyon. No doubt with a PhD in physics and enough computing power to model it, every situation could be explained in terms of lighting angles, wavelengths, etc. Or you can just fit the polarizer on a lens and give er a try. Over time one figures out when it works and when it doesn't

Does a CPL effect focus? There are too many variables involved for a general statement to cover all scenarios. You're cutting out half of the light to start with. Then the light that is hitting the focus mechanism fits a geometric pattern defined by the filter. And another piece of glass which may or may not be optically "correct" has been introduced into the optical path. So the only possible answer to that question is.. maybe

[Mike Buckley]

This discussion is largely nonsensical. Polarizers are no panacea.

Using the logic of that statement and the details of the rest of your post, it's nonsensical to discuss any photography tool that is no panacea. To the contrary, for me it's always sensical to have a discussion that clears up myths. As an example, if nobody had challenged the statement in Brian's thread that a polarizing filter "won't do anything for strong highlights from reflective surfaces," that myth would have perhaps led others into actually believing that it's true.

[John 2]

................... Does a CPL effect focus? There are too many variables involved for a general statement to cover all scenarios. You're cutting out half of the light to start with. Then the light that is hitting the focus mechanism fits a geometric pattern defined by the filter. And another piece of glass which may or may not be optically "correct" has been introduced into the optical path. So the only possible answer to that question is.. maybe

Just a thought on this subject. There are two types of autofocus - Contrast Detection and Phase detection. Whereas most cameras use a combination of both these days, the early Fuji X series cameras (X-Pro1) relied on just one, contrast detection (I think). As a result, the X-Pro1 focussed more reliably if a vertical edge was included in the focus sensor area than if not. I wondered if in such a situation, a polariser could have an effect on reliable focus performance given it tends to pass light in only one plane i.e. introducing another limitation. I have no knowledge that would allow me to answer that Q myself but I was curious.

PS. The focussing problem is by no means unknown. Other references to it can be found elsewhere on the internet. The following quote from Wiki was also interesting. It seems to have been taken from the Handbook of Optics Second edition vol2, Ch22.19, Bass M:

For modern cameras, a circular polarizer is typically used; this comprises firstly a linear polarizer which performs the artistic function just described, followed by a quarter-wave plate which further transforms the now-linearly polarized light into circularly-polarised light before entering the camera. This additional step avoids problems with auto-focus and light-metering sensors within some cameras, which otherwise may not function reliably with a simple linear polariser.

[Geoff F]

Yes, Circular Polarizing filter; I have just tested it.

It has been wet and windy here for the past few days but this afternoon it brightened a little so I was able to do another test in my greenhouse. This image shot with the polarizer on will demonstrate my original starting point. This hoverfly has some overly bright hot spots of reflected light from its hard shiny body. The polarizer may be helping to some extent but it will not be a total cure for this problem. Other solutions will be required and at the end of the day some clone work will probably be the only full answer.



And with the polarizer off but with one stop of under exposure compensation.

[george013]

Yes, Circular Polarizing filter; I have just tested it.

It has been wet and windy here for the past few days but this afternoon it brightened a little so I was able to do another test in my greenhouse. This image shot with the polarizer on will demonstrate my original starting point. This hoverfly has some overly bright hot spots of reflected light from its hard shiny body. The polarizer may be helping to some extent but it will not be a total cure for this problem. Other solutions will be required and at the end of the day some clone work will probably be the only full answer.



And with the polarizer off but with one stop of under exposure compensation.

I don't know what to compare anymore if you also add a -1 EC to it.

George

[pnodrog]

I don't know what to compare anymore if you also add a -1 EC to it.

George

And the bee has moved...

[Geoff F]

Unfortunately it takes a little while of fiddling around to remove a polarizer and hoverflies aren't the most patient of insects.

[JohnRostron]

I would have thought that the best way to test the efficiacy of the polarizer in such circumstances was to take two shots in quick succession, rotating the polarizer through 90 degrees between the two shots. No need for any exposure compensation adjustments.

John

[Geoff F]

This was on the darkest adjustment. I did take a few other shots with different options.