So, how polarizing is polarization?

[ggt]

Someone suggested reading Light, Science and Magic.

Being a dutiful CIC member and dedicated student I ordered it and am near the end of the 3rd chapter. I am totally confused by polarization and have decided that pigment is much easier to digest that anything to do with light.

Do I have to understand polarization or can I just slog on and hope it makes sense later?

Thanks!

ggt

[John Morton]

Hi, Gretchen;

Polarization is a good thing to know. Try thinking about it this way: light travels in waves, so it oscillates, or, moves up and down. A polarizing material is like a picket fence, with alternating transparent and opaque strips: so if the light waves are moving up and down, they will pass between the pickets in the fence; and if they are moving side to side, at right angles (90 degrees) to the pickets, they will be blocked.

Modern 3-D movies make use of this with glasses that have one lens polarized for side-to-side and one lens polarized to up-and-down; that way, each eye can receive a different image from the same screen and the illusion of depth and distance can be created (much better than the old blue and red lensed glasses).

Light that is bouncing off of a flat surface will tend to be aligned with that surface, which is called the plane of reflection; so generally speaking, reflections tend to be something that can be blocked with a polarized filter. These filters are rotated until they match the plane of reflection, which will then allow the camera to shoot clearly through windows, out of airplanes, into water, and so on without reflections interfering with the image.

Sometimes one polarizer will be put over a light source, and another at a different angle over the camera lens; this will remove reflections from objects being photographed using that light (such as watches, glassware, or any shiny product that needs to be presented without distracting reflections and hot spots from the lighting used to photograph it). But if you have two polarizers at right angles, they will pretty much block out all light.

Hope that helps a bit!

[Ken MT]

Have a look at "Choosing a Camera Lens Filter: Polarizers, UV, ND & GND" under lenses in CIC tutorials. This may help to understand some of the concepts. Look under camera equipment tutorial

[Mike Buckley]

Gretchen,

The book's explanation of polarization is the easiest explanation to understand that I have ever seen. However, I came upon it decades after consistently using a polarizer filter for outdoor shots, so I imagine that context was very helpful.

If you haven't ever used a polarizer, borrow one from a friend. When the sun is relatively low (any day before 10:00am or after 3:00pm will work fine where you live), position yourself so the sun is to your left or right. Point your camera toward a blue sky, ideally one that has a few clouds and less ideally one that has no clouds. The closer you point to the horizon, the better. As you rotate the polarizer, notice the change to the appearance of the sky in the viewfinder.

Then point your camera toward some grass or green leaves of plants when sunlight is shining directly on them. As you rotate your polarizer, notice that most if not all of the glare is minimized or eliminated once the polarizer is rotated to a particular position.

Though doing the above won't demonstrate why the appearance of the image is changing (that's what the book does), it does demonstrate that polarizing the light results in dramatically noticeable change. In the beginning of your learning process, I think that's perhaps the most important thing before moving on. Even so, I'm confident that as I continue to make images in my makeshift studio, I'll be returning to that part of the book many times as a refresher course.

[rpcrowe]

I do understand the theory of polarization of light. However, IMO, the most important thing to understand is what a polarizing filter will do (or not do) to and for your image. How and why it happens may be fun for some folks to delve into but, IMO, you don't really need to understand the theory of polarization to understand how to work with a polarizing filter.

An anology is that you don't really need to understand the intracacies of the internal combustion engine to drive your vehicle to the store for a container of milk.

[ggt]

Thanks everyone, I think this is something I will have to learn by doing and playing. Borrowing a filter is a good idea, Mike, but my Cybershot doesn't seem to have any ability to accept accoutrements. I might have to DIY something.

After sleeping on it, it seems a bit clearer. It may just take time for the little gray cells to absorb it all.

[ggt]

Ok, I think I've figured-out what I'm having trouble with. The Word "ray" in light ray. If a "ray" starts with a "point" and extends off into never-never-land . . .how can it be horizontal or vertical? How can a point be either?

Or am I thinking too much geometry here? Is the horizontal or vertical the direction the "atoms" vibrate within the ray?

[Mike Buckley]

my Cybershot doesn't seem to have any ability to accept accoutrements.

There have been a few times that I have had to make a quick shot to capture a moment in time but diddn't have the luxury of being able to screw on the polarizer filter. You'll be able to see the effect of the polarizer using the instructions in my previous post if you hold a filter in one hand in front of the lens so long as it is at least a little bigger than your lens. As you hold the camera in the other hand, or better yet positioned on a tripod, you'll see the exact same effects as if the polarizer was screwed onto the lens.

[rpcrowe]

Thanks everyone, I think this is something I will have to learn by doing and playing. Borrowing a filter is a good idea, Mike, but my Cybershot doesn't seem to have any ability to accept accoutrements. I might have to DIY something.

Gretchen, when I shot with my first digital camera, an Olympus C5050Z point and shoot it did not have the capability to mount a CPL filter or to view the filter's effects through the lens.

I simply held the filter in my hand and rotated the front element until the effect was as I liked it and then hand-held it over the lens. It worked fine but, was a bit of a PITA.

[Dave Humphries]

Hi Gretchen,

There's nothing like "seeing and believing".

After reviewing a few videos that misled, this amateur one actually shows the effect quite well.

The guy is just continuously rotating it and you can see that at one moment it is effective at darkening the side of the car and the next moment at darkening the roof, hood/bonnet and windscreen, same with the puddle - although he's not at the optimum angle for that, so the house never completely disappears.



Cheers,

[Dave Humphries]

and here's another, showing their use for reflection killing;



The point is, you don't need to attach it to your camera to see how it works, just playing with one is enough

[ggt]

Dave, you are awesome!!!!

Thanks for taking the time to post these, they are helpful!

[John Morton]

Ok, I think I've figured-out what I'm having trouble with. The Word "ray" in light ray. If a "ray" starts with a "point" and extends off into never-never-land . . .how can it be horizontal or vertical? How can a point be either?

Or am I thinking too much geometry here? Is the horizontal or vertical the direction the "atoms" vibrate within the ray?

Hi, Gretchen;

Well the thing to remember is that light expands from a source as a wave front, like a bubble expanding outward. That's an important point to know because that means the intensity of light drops geometrically as you move away from its source: so for instance if you are taking photographs of a band using available light and you move back four times as far from the stage, you will only have one sixteenth of the light light reaching you. Move back five times as far, and you only have one twenty-fifth as much light!

So yes light moves in a straight line, as a ray, but it spreads outward as a wave front - just like when a stone is tossed into water and the ripples spread outward, only in three dimensions (not just on the surface of the water).

Now, not only is that light spreading out in all directions; it is also itself vibrating in all directions as it is moving outward: up, down, and every degree of sideways. If it hits a flat surface, the three dimensional wave front of light bounces off as a two dimensional plane and this is the reflection that a polarizer is designed to neutralize. Since light is normally vibrating in all directions, a polarizer will always darken anything you look at through it; but if you have light that is vibrating in a flat plane, such as a reflection, then a polarizer can block that entirely if you rotate it to the right orientation.

If you have light vibrating all the same way and aligned so that all the peaks in the waves are together and all the troughs in the waves are together, then you have a very special kink of light ray - a laser beam.

[ggt]

John,

Thank you! It's all so very cool. What should be most simple things to understand in life and the world are always the most difficult to absorb. you explanation has helped a lot.

I appreciate the time you took to answer.

[John Morton]

Happy to have helped, Gretchen, and I really enjoy photography so anything that gets me thinking about it is a pleasure ;-)