Lens Filter Question

[johnjarosz(jj)]

I'm working on a project for a group I belong to & went to Wilkinson Point this morning just to look at the weed growth along the shore. No camera along, just doing some preliminary homework.
Anyway, the water was calm & I could easily make out the slope of the bottom & weed growth along the shore's sloped bottom. So, I'm thinking that that's a pic I'll have to take in the future. I'm also wearing my polarized sunglasses (polarized bifocals in my case). I take off my sunglasses & I'm not seeing any weeds. I put them back on and I see a nice photo op.
Are polarizing filters made? Do I need to get one to take pics of what is under the surface of the H2O? I was standing up high & looking down into the H2O. Thx.

[juliuspmccann]

This is from Wikipedia. Basically yes, you need the filter to penetrate the reflective quality of water

A polarizing filter or polarising filter is often placed in front of the camera lens in photography in order to darken skies, manage reflections, or suppress glare from the surface of lakes or the sea. Since reflections (and sky-light) tend to be at least partially linearly-polarized, a linear polarizer can be used to change the balance of the light in the photograph. The rotational orientation of the filter is adjusted for the preferred artistic effect. 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 filters 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.

Light reflected from a non-metallic surface becomes polarized; this effect is maximum at Brewster's angle, about 56° from the vertical for common glass (light reflected from metal is not polarized, due to the electromagnetic nature of light). A polarizer rotated to pass only light polarized in the direction perpendicular to the reflected light will absorb much of it. This absorption allows glare reflected from, for example, a body of water or a road to be much reduced. Reflections from shiny surfaces (e.g. vegetation, sweaty skin, water surfaces, glass) are also reduced. This allows the natural colour and detail of what is beneath to come through. Reflections from a window into a dark interior can be much reduced, allowing it to be seen through. (The same effects are available for vision by using polarizing sunglasses.)

Some of the light coming from the sky is polarized (bees use this phenomenon for navigation[2]). The electrons in the air molecules cause a scattering of sunlight in all directions. This explains why the sky is not dark during the day. But when looked at from the sides, the light emitted from a specific electron is totally polarized.[3] Hence, a picture taken in a direction at 90 degrees from the sun can take advantage of this polarization. Actually, the effect is visible in a band of 15° to 30° measured from the optimal direction. Use of a polarizing filter, in the correct direction, will filter out the polarized component of skylight, darkening the sky; the landscape below it, and clouds, will be less affected, giving a photograph with a darker and more dramatic sky, and emphasizing the clouds.[4] Perpendicularly incident light waves tend to reduce clarity and saturation of certain colors, which increases haziness. The polarizing lens effectively absorbs these light waves, rendering outdoor scenes crisper with deeper color tones in subject matter such as blue skies, bodies of water and foliage.[5]

Much light is differentiated by polarization, e.g. light passing through crystals like sunstones (calcite) or water droplets producing rainbows. The polarization of the rainbow is caused by the internal reflection. The rays strike the back surface of the drop close to the Brewster angle.[1]

Polarizing filters can be rotated to maximise or minimise admission of polarised light. They are mounted in a rotating collar for this purpose - one need not screw or unscrew the filter to adjust the effect. Rotating the polarizing filter will make rainbows, reflections, and other polarized light stand out or nearly disappear depending on how much of the light is polarized and the angle of polarization.

The benefits of polarizing filters are the same in digital or film photography. While software post-processing can simulate many other types of filter, a photograph does not record the light polarization, so the effects of controlling polarization at the time of exposure cannot be replicated in software.

[johnbenish]

I can add that sometimes in rippled water the circular polarizer does some strange effects though I haven't tried a study of it I would think that the effects change with the angle and brightness of the sun. Don't know if many have tried an old film type straight line polarized filter with digital, I got weird effects, which was about what the people I've talked said to expect.

[johnjarosz(jj)]

...The project I'm working on is for L. Erie so hoping for the calm water that I would prefer might be expecting too much. What kind of "weird effects" did you get, John, with an old film type polarizer?

Would time of day make any difference, i.e. high sun vs. low angle?
Thanks guys

[johnbenish]

I don't remember much except weird light patterns, not much for images. I guess I should have tried more, but I don't have a lens now I could do that with since I got rid of my film stuff. Would be fun to try it though, the only consideration is if any harm is done to the sensor, can't see why there would be by a shot or two, but a lot of exposures?
I think Nick would know the reasoning behind why the circular vs. line polarizing filter with digital. I've never really been happy with the circular polarizing filters I have, they seem to get ok color in glare situations but with flat-plane glare they don't perform as well as I'd like. Guess that's a long way of saying that I don't get pictures through the camera that are as good as I see through my good polarizing glasses. Maybe it's the cameraman.

[johnjarosz(jj)]

Thanks for the help! If it's the cameraman, I'm in big trouble already!! There's no hope for me.