In reply to Rob Exile Ward:
The sunglasses aren't filtering out wavelengths that don't focus; the eye does the focusing for all incoming light.
It works either by polarizing the light, or by filtering for a specific colour.
Polarizers remove the 'disorganised' effect of light that has been scattered by reflections or atmospheric conditions, and produces clearer lines and less glare, which can also help you to perceive contrast and clarity.
Similarly, filtering for a colour can remove distractions and change the balance of an image. For instance, an orange filter will tend to make skies look a bit darker (because they are mainly blue and don't pass the filter), grass (which often glares) will be a touch darker because of its blue component, but earth and skin colours will stay fairly bright. B&W photographers used to use colour filters lots to change the balance of the picture, since the effect on colours was obviously not visible. These days you can do similar things in post processing, though some B&W specialists still use filters.
A UV filter is similar to the last type, and works by filtering out UV. This creates a purple, hazy light that dissipates over landscapes, particularly where there are particles or dust in the air. Scattered UV can have a 'veiling' effect that reduces contrast and apparent sharpness. Landscape photographers use these filters quite a bit to create crisp images with long sitelines.
Post edited at 14:26