Slow Shutter Speed and White Balance

[navcom]

Originally Posted by lynweber

ND Filter what's that. Polarizer is something you want on a bright sunny day? Just making sure I understand.

Osmosis is right. Think of a neutral density filter like tinting on your car windows. You can still see everything the same as before except that it's all darker. ND filters don't alter the quality of the light...just it's intensity. It's like turning down the sun and artificially making it darker outside.

A circular polarizer DOES alter the light coming in. It is used mainly to remove reflections such as light reflections coming off water droplets on leaves or reflections on glass. They are not designed to limit light (though they do a bit because of the coating required to limit reflections). They also modify colors such as darkening the blue in the sky. It's just like wearing polarized sun glasses...same theory. They make colors more vivid and cut down on reflections.

Hope that helps!

[kab]

Originally Posted by lynweber

... Polarizer is something you want on a bright sunny day? Just making sure I understand.

Have you ever worn polarized sunglasses? Tilt your head one way and the sky gets a lot darker, other way it gets lighter. Cuts glare off of water and other shiny surfaces so you can see better in harsh sunlight. That's your basic polarizing filter.

Polarizers are great for deepening the blue of summer skies and making clouds stand out; for cutting reflected glare from water (classic - you retain the surface, but can also see what is under the water), glass -- and (crucially) from foliage. Yes, shiny green leaves especially frequently benefit from a polarizing filter.

Polarizers are typically not good outdoors with wide-angle lenses (the blocking effect changes with the orientation to your light source, e.g., the sun, and over a wide angle that means some parts a darkened much more than others and you get unpleasant/unnatural banding).

Light comes in waves, basically little 2D sine curves, but each photon may be oriented vertically, horizontally, or anything in between. Polarizing filters block light waves that are not oriented to match the filter -- so, yes, you can (and should!) rotate the polarizer and see how it will change the affect. Two polarizers at right angles will block a whole lot of light! But, combined with long exposure, two stacked polarizers is a strategy used for accurately recording museum paintings and such with harsh lighting and no flash.

A polarizer is one of the very few filters that you cannot do post-process -- if you don't record what's under the water, you can't do anything about it later! This filter is worth learning in some detail. Lots of uses besides bright sunshine (where it is often over-used to get near-black skies and garish clouds, but that's a matter of taste).

From the original request, though, to catch a motion of wheat, a polarizer is probably not the way to go. The effect you want may be better with some diffuse, dreamy early or late light, or even heat waves, and that isn't usually a good use for a polarizer.

Another general note about filters: They all block light, which means you have to adjust exposure. Most cameras w/ Through-The-Lens (TTL) metering do this automatically, but if you are going the full-manual mode, you may need to be even more careful w/ exposure.